HOME

TheInfoList




Birds are a group of
warm-blooded Warm-blooded is an informal term referring to animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as ...
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
s constituting the
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently f ...
Aves , characterised by
feather Feathers are epidermal growths that form a distinctive outer covering, or plumage Plumage ( "feather") is a layer of feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on dinosaurs, both avi ...

feather
s, toothless beaked jaws, the
laying Laying is the act of making equipment level. It usually involves moving equipment in small motions so that spirit level A spirit level, bubble level, or simply a level, is an Measuring instrument, instrument designed to indicate whether ...
of hard-shelled eggs, a high
metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cell ...

metabolic
rate, a four-chambered
heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use ...

heart
, and a strong yet lightweight
skeleton A skeleton is a structural frame that supports an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consu ...
. Birds live worldwide and range in size from the
bee hummingbird#REDIRECT Bee hummingbird {{Redirect category shell, 1= {{R from move {{R from other capitalisation ...
to the
ostrich ''Struthio'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circums ...

ostrich
. There are about ten thousand living species, more than half of which are
passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), bi ...
, or "perching" birds. Birds have whose development varies according to species; the only known groups without wings are the extinct
moa Moa (order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such ...

moa
and
elephant bird Elephant birds are members of the extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bi ...

elephant bird
s. Wings, which evolved from
forelimb A forelimb or front limb is one of the bilateral symmetry, paired joint, articulated appendages (limb (anatomy), limbs) attached on the cranial (anterior (anatomy), anterior) end of a terrestrial animal, terrestrial tetrapod vertebrate's torso. Wi ...
s, gave birds the ability to fly, although further evolution has led to the loss of flight in some birds, including
ratite A ratite () is any of a diverse group of mostly flightless s are a well-known example of flightless birds. Flightless birds are birds that through evolution lost the ability to flight, fly. There are over 60 extant species, including the well ...

ratite
s,
penguin Penguins (order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and t ...

penguin
s, and diverse
endemic Endemism is the state of a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest gro ...
island species. The digestive and respiratory systems of birds are also uniquely adapted for flight. Some bird species of aquatic environments, particularly
seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

seabird
s and some
waterbirds A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystems, although others make no distinction from seabirds ...

waterbirds
, have further evolved for swimming. Birds are a group of
feathered
feathered
theropod Theropoda ( from Ancient Greek, Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three-toed limbs. Theropods are generally classed as a group of saurischian d ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
s and constitute the only living dinosaurs. Likewise, birds are considered
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s in the modern
cladistic Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...

cladistic
sense of the term, and their closest living relatives are the
crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

crocodilia
ns. Birds are descendants of the primitive avialans (whose members include ''
Archaeopteryx ''Archaeopteryx'' ( "old wing"), sometimes referred to by its German name, ' ("original bird" or "first bird"), is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification ...

Archaeopteryx
'') which first appeared about 160 million years ago (mya) in China. According to DNA evidence, modern birds (Neornithes) evolved in the Middle to
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 millio ...
, and diversified dramatically around the time of the
Cretaceous–Paleogene extinction event The Cretaceous–Paleogene (K–Pg) extinction event (also known as the Cretaceous–Tertiary extinction) was a sudden extinction event, mass extinction of three-quarters of the plant and animal species on Earth, approximately 66 millio ...
66 mya, which killed off the
pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") were flying reptiles of the extinct clade or Order (biology), order Pterosauria. They existed during most of the Mesozoic: from the late Triassic to the end of the Cretac ...
s and all non-avian dinosaurs. Many
social species Sociality is the degree to which individuals in an animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions ...
pass on knowledge across generations, which is considered a form of culture. Birds are social, communicating with visual signals, calls, and
songs A song is a musical composition Musical composition can refer to an Originality, original piece or work of music, either Human voice, vocal or Musical instrument, instrumental, the musical form, structure of a musical piece or to the p ...
, and participating in such behaviours as
cooperative breeding Cooperative breeding is a social system In , social system is the patterned network of relationships constituting a coherent whole that exist between individuals, groups, and institutions. It is the formal of role and status that can form in a ...
and hunting, flocking, and
mobbing Mobbing, as a sociological term, means bullying Bullying is the use of force, coercion Coercion () is compelling a party to act in an involuntary manner by use of threat A threat is a communication of intent to inflict harm or loss ...
of predators. The vast majority of bird species are socially (but not necessarily sexually)
monogamous Monogamy ( ) is a form of dyadic relationship Relationship most often refers to: * Interpersonal relationship The concept of interpersonal relationship involves social associations, connections, or affiliations between two or more peo ...
, usually for one breeding season at a time, sometimes for years, but rarely for life. Other species have breeding systems that are
polygynous Polygyny (; from Neoclassical Greek πολυγυνία from πολύ- ''poly-'' "many", and γυνή ''gyne'' "woman" or "wife") is the most common and accepted form of polygamy Polygamy (from Greek language, Late Greek , ''polygamí ...
(one male with many females) or, rarely,
polyandrous Polyandry (; from grc-gre, πολυ- ''poly-'', "many" and ἀνήρ ''anēr'', "man") is a form of polygamy Polygamy (from Greek language, Late Greek , ''polygamía'', "state of marriage to many spouses") is the practice of marriage, ma ...
(one female with many males). Birds produce offspring by laying eggs which are fertilised through
sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process Biological processes are those processes that are vital for an organism In biology, an organism (from Ancient Greek, ...
. They are usually laid in a nest and incubated by the parents. Most birds have an extended period of parental care after hatching. Many species of birds are economically important as food for human consumption and raw material in manufacturing, with
domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable supply of resources from that sec ...

domesticated
and undomesticated birds being important sources of eggs, meat, and feathers.
Songbird A songbird is a bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biologi ...

Songbird
s, parrots, and other species are popular as pets.
Guano Guano (Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambiguatio ...

Guano
(bird excrement) is harvested for use as a fertiliser. Birds figure throughout human culture. About 120 to 130 species have become
extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
due to human activity since the 17th century, and hundreds more before then. Human activity threatens about 1,200 bird species with extinction, though efforts are underway to protect them. Recreational
birdwatching Birdwatching, or birding, is a form of wildlife observation Wildlife observation is the practice of noting the occurrence or abundance of animal species at a specific location and time, either for research purposes or recreation. A common e ...

birdwatching
is an important part of the
ecotourism Ecotourism is a form of tourism at the archaeological site of Chichén Itza. in Vienna. Tourism is travel for pleasure or business; also the theory and practice of touring (disambiguation), touring, the business of attracting, accommodating ...
industry.


Evolution and classification

The first
classification Classification is a process related to categorization Categorization is the human ability and activity of recognizing shared features or similarities between the elements of the experience Experience refers to conscious , an English Paracels ...
of birds was developed by
Francis Willughby Francis Willughby (sometimes spelt Willoughby) FRS FRS may also refer to: Government and politics * Facility Registry System, a centrally managed Environmental Protection Agency database that identifies places of environmental interest in t ...
and
John Ray John Ray Fellow of the Royal Society, FRS (29 November 1627 – 17 January 1705) was a Christian England, English Natural history, naturalist widely regarded as one of the earliest of the English parson-naturalists. Until 1670, he wrote his na ...

John Ray
in their 1676 volume ''Ornithologiae''.
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement Ennoblement is the conferring of nobility—the induction of an individual into the noble social class, class. Currently only a few kingdoms still grant nob ...

Carl Linnaeus
modified that work in 1758 to devise the
taxonomic classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...
system currently in use. Birds are categorised as the biological class Aves in
Linnaean taxonomy Linnaean taxonomy can mean either of two related concepts: # the particular form of biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical stru ...
.
Phylogenetic taxonomy In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
places Aves in the dinosaur
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
Theropoda Theropoda ( from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

Theropoda
.


Definition

Aves and a sister group, the order
Crocodilia Crocodilia (or Crocodylia, both ) is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, ...

Crocodilia
, contain the only living representatives of the reptile clade Archosauria. During the late 1990s, Aves was most commonly defined
phylogenetically In biology, phylogenetics (from Greek language, Greek wikt:φυλή, φυλή/wikt:φῦλον, φῦλον () "tribe, clan, race", and wikt:γενετικός, γενετικός () "origin, source, birth") is a part of systematics that addresse ...

phylogenetically
as all descendants of the
most recent common ancestor In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
of modern birds and ''
Archaeopteryx lithographica ''Archaeopteryx'' ( "old wing"), sometimes referred to by its German name, ' ("original bird" or "first bird"), is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification ...

Archaeopteryx lithographica
''. However, an earlier definition proposed by
Jacques Gauthier Jacques Armand Gauthier (born June 7, 1948 in New York City New York, often called New York City to distinguish it from New York State New York is a state State may refer to: Arts, entertainment, and media Literature * ''State Maga ...
gained wide currency in the 21st century, and is used by many scientists including adherents of the
Phylocode The ''International Code of Phylogenetic Nomenclature'', known as the ''PhyloCode'' for short, is a formal set of rules governing phylogenetic nomenclature In biology Biology is the natural science that studies life and living organisms, ...
system. Gauthier defined Aves to include only the
crown group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
of the set of modern birds. This was done by excluding most groups known only from
fossils A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication used by humans, inc ...

fossils
, and assigning them, instead, to the broader group Avialae, in part to avoid the uncertainties about the placement of ''Archaeopteryx'' in relation to animals traditionally thought of as theropod dinosaurs. Gauthier and de Queiroz identified four different definitions for the same biological name "Aves", which is a problem. The authors proposed to reserve the term Aves only for the crown group consisting of the last common ancestor of all living birds and all of its descendants, which corresponds to meaning number 4 below. He assigned other names to the other groups. # Aves can mean all
archosaur Archosauria ("ruling reptiles") is a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), l ...
s closer to birds than to
crocodile Crocodiles (family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society. I ...

crocodile
s (alternately
Avemetatarsalia Avemetatarsalia (meaning "bird metatarsal The metatarsal bones, or metatarsus are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, th ...
) # Aves can mean those advanced archosaurs with feathers (alternately
Avifilopluma Avifilopluma ("bird filoplumes") is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, composed of a common ancestor ...
) # Aves can mean those feathered dinosaurs that fly (alternately
Avialae Avialae ("bird wings") is a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal de ...
) # Aves can mean the last common ancestor of all the currently living birds and all of its descendants (a "
crown group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
", in this sense synonymous with Neornithes) Under the fourth definition ''Archaeopteryx'', traditionally considered one of the earliest members of Aves, is removed from this group, becoming a non-avian dinosaur instead. These proposals have been adopted by many researchers in the field of palaeontology and
bird evolution Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a four-c ...
, though the exact definitions applied have been inconsistent. Avialae, initially proposed to replace the traditional fossil content of Aves, is often used synonymously with the vernacular term "bird" by these researchers. Most researchers define Avialae as branch-based clade, though definitions vary. Many authors have used a definition similar to "all
theropod Theropoda ( from Ancient Greek, Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three-toed limbs. Theropods are generally classed as a group of saurischian d ...
s closer to birds than to ''
Deinonychus ''Deinonychus'' ( ; from el, δεινός , 'terrible' and , genitive 'claw') is a genus of Dromaeosauridae, dromaeosaurid Theropoda, theropod dinosaur with one described species, ''Deinonychus antirrhopus''. This species, which could grow ...

Deinonychus
''",Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (eds.) (2004). ''The Dinosauria'', Second Edition. University of California Press., 861 pp. with ''
Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a former wastebasket taxon Wastebasket taxon (also called a wastebin taxon, dustbin taxon or catch-all taxon) is a term used by some taxonomists In biology Biology is the natural sci ...

Troodon
'' being sometimes added as a second external specifier in case it is closer to birds than to ''Deinonychus''. Avialae is also occasionally defined as an apomorphy-based clade (that is, one based on physical characteristics).
Jacques Gauthier Jacques Armand Gauthier (born June 7, 1948 in New York City New York, often called New York City to distinguish it from New York State New York is a state State may refer to: Arts, entertainment, and media Literature * ''State Maga ...
, who named Avialae in 1986, re-defined it in 2001 as all dinosaurs that possessed feathered
wing A wing is a type of fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force describ ...

wing
s used in flapping
flight Flight or flying is the process by which an object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Entity, something that is tangible and within the grasp of the senses ** Object (abstract), an o ...
, and the birds that descended from them.Gauthier, J., and de Queiroz, K. (2001). "Feathered dinosaurs, flying dinosaurs, crown dinosaurs, and the name Aves." pp. 7–41 in ''New perspectives on the origin and early evolution of birds: proceedings of the International Symposium in Honor of John H. Ostrom'' (J.A. Gauthier and L.F. Gall, eds.). Peabody Museum of Natural History, Yale University, New Haven, CTGauthier, J. (1986). "Saurischian monophyly and the origin of birds." In: K. Padian, ed. ''The origin of birds and the evolution of flight.'' San Francisco: California, Acad. Sci. pp. 1–55. (Mem. Calif. Acad. Sci.8.) Despite being currently one of the most widely used, the crown-group definition of Aves has been criticised by some researchers. Lee and Spencer (1997) argued that, contrary to what Gauthier defended, this definition would not increase the stability of the clade and the exact content of Aves will always be uncertain because any defined clade (either crown or not) will have few synapomorphies distinguishing it from its closest relatives. Their alternative definition is synonymous to Avifilopluma.


Dinosaurs and the origin of birds

Based on fossil and biological evidence, most scientists accept that birds are a specialised subgroup of
theropod Theropoda ( from Ancient Greek, Greek 'wild beast' and 'foot'), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three-toed limbs. Theropods are generally classed as a group of saurischian d ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 annum, million years ago, although the exact origin and timing of the evolution ...

dinosaur
s, and more specifically, they are members of
Maniraptora Maniraptora is a clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - ...
, a group of theropods which includes dromaeosaurids and
oviraptorosaurs Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period (geology), Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like s ...

oviraptorosaurs
, among others. As scientists have discovered more theropods closely related to birds, the previously clear distinction between non-birds and birds has become blurred. Recent discoveries in the
Liaoning Liaoning (), is a coastal province A province is almost always an administrative division Administrative division, administrative unitArticle 3(1). , country subdivision, administrative region, subnational entity, first-level subdivisi ...
Province of northeast China, which demonstrate many small theropod
feathered dinosaurs A feathered dinosaur is any species of dinosaur possessing feathers. While this includes all species of birds, there is a hypothesis that many, if not all non-avian dinosaur species also possessed feathers in some shape or form. However, Profess ...
, contribute to this ambiguity. The consensus view in contemporary
palaeontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (geology), epoch (roughly 11,700 years before present). It includes th ...
is that the flying theropods, or avialans, are the closest relatives of the deinonychosaurs, which include dromaeosaurids and
troodontid Troodontidae is a family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the ...
s. Together, these form a group called
Paraves Paraves are a widespread group of theropod dinosaurs that originated in the Late Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and scansoriopterygidae, scansoriopterygids, the group also contains th ...
. Some
basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a minimal level that is neces ...
members of Deinonychosauria, such as ''
Microraptor ''Microraptor'' (Greek language, Greek, μικρός, ''mīkros'': "small"; Latin language, Latin, ''raptor'': "one who seizes") is a genus of small, four-winged dromaeosaurid dinosaurs. Numerous well-preserved fossil specimens have been recovere ...

Microraptor
'', have features which may have enabled them to glide or fly. The most basal deinonychosaurs were very small. This evidence raises the possibility that the ancestor of all paravians may have been
arboreal Arboreal locomotion is the locomotion Locomotion means the act or ability of an entity or person to transport or move oneself from place to place. Locomotion or Loco-Motion may refer to: Motion * Motion (physics) *Specific types of motion ** A ...
, have been able to glide, or both. Unlike ''Archaeopteryx'' and the non-avialan feathered dinosaurs, who primarily ate meat, recent studies suggest that the first avialans were
omnivore An omnivore () is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been — ...
s. The
Late Jurassic The Late Jurassic is the third epoch In chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the modern science of chronology Chronology (from Latin Latin (, or , ) is a classical language belonging to the Italic ...
''Archaeopteryx'' is well known as one of the first
transitional fossil A transitional fossil is any fossil A fossil (from Classical Latin Classical Latin is the form of Latin language Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languag ...
s to be found, and it provided support for the
theory of evolution Evolution is change in the Heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes that are passed on from parent to offsp ...
in the late 19th century. ''Archaeopteryx'' was the first fossil to display both clearly traditional reptilian characteristics—teeth, clawed fingers, and a long, lizard-like tail—as well as wings with flight feathers similar to those of modern birds. It is not considered a direct ancestor of birds, though it is possibly closely related to the true ancestor.


Early evolution

Over 40% of key traits found in modern birds evolved during the 60 million year transition from the earliest bird-line archosaurs to the first maniraptoromorphs, i.e. the first dinosaurs closer to living birds than to ''
Tyrannosaurus rex ''Tyrannosaurus'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy) ...

Tyrannosaurus rex
''. The loss of osteoderms otherwise common in archosaurs and acquisition of primitive feathers might have occurred early during this phase. After the appearance of Maniraptoromorpha, the next 40 million years marked a continuous reduction of body size and the accumulation of
neotenic Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-d ...

neotenic
(juvenile-like) characteristics.
Hypercarnivory A hypercarnivore is an animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular ...
became increasingly less common while braincases enlarged and forelimbs became longer. The
integument In biology, integument is the natural covering of an organism or an organ, such as its skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, an ...
evolved into complex, pennaceous feathers. The oldest known paravian (and probably the earliest avialan) fossils come from the
Tiaojishan Formation The Tiaojishan Formation is a geological formation in Hebei and Liaoning, People's Republic of China, dating to the middle-late Jurassic period (Bathonian-Oxfordian (stage), Oxfordian stages). It is known for its Lagerstätte, exceptionally preserve ...

Tiaojishan Formation
of China, which has been dated to the late
Jurassic The Jurassic ( ) is a geologic period The geologic time scale (GTS) is a system of chronological dating that classifies Geology, geological strata (stratigraphy) in time. It is used by geologists, paleontology, paleontologists, and other earth ...
period ( Oxfordian stage), about 160 million years ago. The avialan species from this time period include '''', '' Xiaotingia zhengi'', and '' Aurornis xui''. The well-known probable early avialan, ''Archaeopteryx'', dates from slightly later Jurassic rocks (about 155 million years old) from
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...

Germany
. Many of these early avialans shared unusual anatomical features that may be ancestral to modern birds, but were later lost during bird evolution. These features include enlarged claws on the second toe which may have been held clear of the ground in life, and long feathers or "hind wings" covering the hind limbs and feet, which may have been used in aerial manoeuvreing. Avialans diversified into a wide variety of forms during the
Cretaceous Period The Cretaceous (, ) is a geological period that lasted from about 145 to 66 mya (unit), million years ago (mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At nearly 80 million years, it is the long ...
. Many groups retained primitive characteristics, such as clawed wings and teeth, though the latter were lost independently in a number of avialan groups, including modern birds (Aves). Increasingly stiff tails (especially the outermost half) can be seen in the evolution of maniraptoromorphs, and this process culminated in the appearance of the
pygostyle Pygostyle describes a skeletal condition in which the final few caudal vertebra In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of wh ...
, an ossification of fused tail vertebrae. In the late Cretaceous, about 100 million years ago, the ancestors of all modern birds evolved a more open pelvis, allowing them to lay larger eggs compared to body size. Around 95 million years ago, they evolved a better sense of smell. A third stage of bird evolution starting with
Ornithothoraces Ornithothoraces is a group of avialan Avialae ("bird wings") is a clade A clade (; from grc, , ''klados'', "branch"), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic—that is, ...
(the "bird-chested" avialans) can be associated with the refining of aerodynamics and flight capabilities, and the loss or co-ossification of several skeletal features. Particularly significant are the development of an enlarged, keeled sternum and the
alula The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; it is the diminutive of ''ala'', meaning "wing". The alu ...

alula
, and the loss of grasping hands.


Early diversity of bird ancestors

The first large, diverse lineage of short-tailed avialans to evolve were the
Enantiornithes The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans ("birds" in the broad sense), the most abundant and diverse group known from the Mesozoic era The Mesozoic Era ( ), also call ...
, or "opposite birds", so named because the construction of their shoulder bones was in reverse to that of modern birds. Enantiornithes occupied a wide array of
ecological niche In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms ...

ecological niche
s, from sand-probing shorebirds and fish-eaters to tree-dwelling forms and seed-eaters. While they were the dominant group of avialans during the Cretaceous period, enantiornithes became extinct along with many other dinosaur groups at the end of the
Mesozoic era The Mesozoic Era ( ), also called the Age of Reptiles and the Age of Conifers, is the second-to-last era An era is a span of time defined for the purposes of chronology 222px, Joseph Scaliger's ''De emendatione temporum'' (1583) began the ...
. Many species of the second major avialan lineage to diversify, the
Euornithes Euornithes (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approximately 10.7 milli ...
(meaning "true birds", because they include the ancestors of modern birds), were semi-aquatic and specialised in eating fish and other small aquatic organisms. Unlike the Enantiornithes, which dominated land-based and arboreal habitats, most early euornithes lacked perching adaptations and seem to have included shorebird-like species, waders, and swimming and diving species. The latter included the superficially
gull Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns (family Sternidae) and only distantly related to auks, Skimmer (bird), skimmers and even more distantly to wade ...

gull
-like ''
Ichthyornis ''Ichthyornis'' (meaning "fish bird", after its fish-like vertebrae) is an extinct genus of toothed seabird-like ornithuran from the late Cretaceous The Cretaceous (, ) is a geological period that lasted from about 145 to 66 million years ag ...

Ichthyornis
'' and the
Hesperornithiformes Hesperornithes is an extinct and highly specialized group of aquatic avialans closely related to the ancestors of modern bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by f ...
, which became so well adapted to hunting fish in marine environments that they lost the ability to fly and became primarily aquatic. The early euornithes also saw the development of many traits associated with modern birds, like strongly keeled breastbones, toothless, beaked portions of their jaws (though most non-avian euornithes retained teeth in other parts of the jaws). Euornithes also included the first avialans to develop true
pygostyle Pygostyle describes a skeletal condition in which the final few caudal vertebra In the vertebrate spinal column, each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, the proportions of wh ...
and a fully mobile fan of tail feathers, which may have replaced the "hind wing" as the primary mode of aerial maneuverability and braking in flight. A study on mosaic evolution in the avian skull found that the
last common ancestor In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
of all Neornithes might have had a beak similar to that of the modern hook-billed vanga and a skull similar to that of the
Eurasian golden oriole The Eurasian golden oriole (''Oriolus oriolus'') also called golden oriole, is the only member of the Old World oriole The Old World orioles (Oriolidae) are an Old World The Old World consists of Africa Africa is the world's s ...
. As both species are small aerial and canopy foraging
omnivore An omnivore () is an animal Animals (also called Metazoa) are organisms that form the Animalia. With few exceptions, animals , , are , can , and grow from a hollow sphere of , the , during . Over 1.5 million animal have been — ...
s, a similar ecological niche was inferred for this hypothetical ancestor.


Diversification of modern birds

All modern birds lie within the
crown group In phylogenetics In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, p ...
Aves (alternately Neornithes), which has two subdivisions: the
Palaeognathae Palaeognathae (; ) is a clade of birds, called paleognaths, within the subclass Neornithes of the class (biology), class Aves. It is one of the two extant taxon, extant infraclasses of birds, the other being Neognathae, both of which form Neorni ...
, which includes the flightless
ratite A ratite () is any of a diverse group of mostly flightless s are a well-known example of flightless birds. Flightless birds are birds that through evolution lost the ability to flight, fly. There are over 60 extant species, including the well ...

ratite
s (such as the
ostrich ''Struthio'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circums ...

ostrich
es) and the weak-flying
tinamou Tinamous () form an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, ...
s, and the extremely diverse
Neognathae Neognaths (Neognathae , from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the follow ...

Neognathae
, containing all other birds. These two subdivisions are often given the
rank Rank is the relative position, value, worth, complexity, power, importance, authority, level, etc. of a person or object within a ranking A ranking is a relationship between a set of items such that, for any two items, the first is either "rank ...
of
superorder In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions ...
, although Livezey and Zusi assigned them "cohort" rank. Depending on the
taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific classification scheme. Originally used only about biological ...
viewpoint, the number of known living bird species varies anywhere from 9,800 to 10,758. The discovery of ''
Vegavis ''Vegavis'' is a genus of extinct bird that lived during the Late Cretaceous (Maastrichtian stage) of Antarctica, some 68 to 66 mya (unit), mya. Among modern birds, most studies show that ''Vegavis'' is most closely related to ducks and goose, ge ...
'', a late Cretaceous member of the
Anatidae The Anatidae are the biological family (biology), family of water birds that includes ducks, goose, geese, and swans. The family has a cosmopolitan distribution, occurring on all the world's continents. These birds are adapted for aquatic locomo ...
, proved that the diversification of modern birds started before the
Cenozoic era The Cenozoic Era ( ) meaning "new life" is the current and most recent of the three geological eras of the Phanerozoic The Phanerozoic Eon is the current geologic eon in the geologic time scale The geologic time scale (GTS) is a system of ch ...

Cenozoic era
. The affinities of an earlier fossil, the possible
galliform Galliformes is an order of heavy-bodied ground-feeding bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshel ...

galliform
''
Austinornis ''Austinornis'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer t ...
lentus'', dated to about 85 million years ago, are still too controversial to provide a fossil evidence of modern bird diversification. Most studies agree on a Cretaceous age for the most recent common ancestor of modern birds but estimates range from the
Middle Cretaceous The Cretaceous (, ) is a geological period that lasted from about 145 to 66 million years ago One million (1,000,000), or one thousand thousand, is the natural number In mathematics, the natural numbers are those used for counting (as in " ...
to the latest
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous The Cretaceous ( ) is a that lasted from about 145 to 66 (Mya). It is the third and final period of the , as well as the longest. At around 79 millio ...
. Similarly, there is no agreement on whether most of the early diversification of modern birds occurred before or after the Cretaceous–Palaeogene extinction event. This disagreement is in part caused by a divergence in the evidence; most molecular dating studies suggests a Cretaceous
evolutionary radiation An evolutionary radiation is an increase in taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer to a specific clas ...
, while fossil evidence points to a Cenozoic radiation (the so-called 'rocks' versus 'clocks' controversy). Previous attempts to reconcile molecular and fossil evidence have proved controversial, but more recent estimates, using a more comprehensive sample of fossils and a new way of calibrating
molecular clocks The molecular clock is a figurative term for a technique that uses the mutation rate In genetics Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) Thou ...
, showed that while modern birds originated early in the Late Cretaceous in Western Gondwana, a pulse of diversification in all major groups occurred around the Cretaceous–Palaeogene extinction event. Modern birds expanded from West Gondwana to the Laurasia through two routes. One route was an Antarctic interchange in the Paleogene. This can be confirmed with the presence of multiple avian groups in Australia and New Zealand. The other route was probably through North American, via land bridges during the Paleocene. This allowed the expansion and diversification of Neornithes into the Holarctic and Paleotropics.


Classification of bird orders

Cladogram A cladogram (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

Cladogram
of modern bird relationships based on Kuhl, H. ''et al.'' (2020) The classification of birds is a contentious issue. Sibley and Ahlquist's ''Phylogeny and Classification of Birds'' (1990) is a landmark work on the classification of birds, although it is frequently debated and constantly revised. Most evidence seems to suggest the assignment of orders is accurate, but scientists disagree about the relationships between the orders themselves; evidence from modern bird anatomy, fossils and DNA have all been brought to bear on the problem, but no strong consensus has emerged. More recently, new fossil and molecular evidence is providing an increasingly clear picture of the evolution of modern bird orders.


Genomics

, the
genome In the fields of molecular biology Molecular biology is the branch of biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, M ...

genome
has been sequenced for at least one species in about 90% of extant avian families (218 out of 236 families recognised by the ''Howard and Moore Checklist'').


Distribution

Birds live and breed in most terrestrial habitats and on all seven continents, reaching their southern extreme in the
snow petrel The snow petrel (''Pagodroma nivea'') is the only member of the genus ''Pagodroma.'' It is one of only three birds that has been seen at the Geographic South Pole The South Pole, also known as the Geographic South Pole or Terrestrial So ...
's breeding colonies up to inland in
Antarctica Antarctica ( or ) is Earth's southernmost continent. It contains the geographic South Pole and is situated in the Antarctic region of the Southern Hemisphere, almost entirely south of the Antarctic Circle, and is surrounded by the Southern Oc ...

Antarctica
. The highest bird
diversity Diversity, diversify, or diverse may refer to: Business *Diversity (business) The "business case for diversity" stems from the progression of the models of diversity within the workplace since the 1960s. The original model for diversity was situ ...

diversity
occurs in tropical regions. It was earlier thought that this high diversity was the result of higher
speciation Speciation is the evolutionary process by which populations evolve to become distinct species. The biologist Orator F. Cook coined the term in 1906 for cladogenesis, the splitting of lineages, as opposed to anagenesis, phyletic evolution within ...

speciation
rates in the tropics; however recent studies found higher speciation rates in the high latitudes that were offset by greater
extinction Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...

extinction
rates than in the tropics. Many species migrate annually over great distances and across oceans; several families of birds have adapted to life both on the world's oceans and in them, and some
seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

seabird
species come ashore only to breed, while some
penguin Penguins (order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and t ...

penguin
s have been recorded diving up to deep. Many bird species have established breeding populations in areas to which they have been introduced by humans. Some of these introductions have been deliberate; the
ring-necked pheasant The common pheasant (''Phasianus colchicus'') is a bird in the pheasant family ( Phasianidae). The genus name comes from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European lang ...
, for example, has been introduced around the world as a
game bird Galliformes is an order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qu ...
. Others have been accidental, such as the establishment of wild
monk parakeet The monk parakeet (''Myiopsitta monachus''), also known as the Quaker parrot, is a species of true parrot in the family Psittacidae. It is a small, bright-green parrot with a greyish breast and greenish-yellow abdomen. Its average lifespan is 20 ...

monk parakeet
s in several North American cities after their escape from captivity. Some species, including
cattle egret The cattle egret (''Bubulcus ibis'') is a cosmopolitan Cosmopolitan may refer to: Food and drink * Cosmopolitan (cocktail), also known as a "Cosmo" History * Rootless cosmopolitan, a Soviet derogatory epithet during Joseph Stalin's anti-Se ...

cattle egret
,
yellow-headed caracara The yellow-headed caracara (''Milvago chimachima'') is a bird of prey Birds of prey, also known as raptors, include species of bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characteri ...
and
galah The galah (; ''Eolophus roseicapilla''), also known as the pink and grey cockatoo or rose-breasted cockatoo, is the only species within genus ''Eolophus'' of the cockatoo Family (biology), family. Found throughout Australia, it is among the most ...

galah
, have spread naturally far beyond their original ranges as created suitable new habitat.


Anatomy and physiology

Compared with other vertebrates, birds have a
body plan A body plan, ''Bauplan'' (German plural ''Baupläne''), or ground plan is a set of morphological features common to many members of a phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ) ...
that shows many unusual adaptations, mostly to facilitate
flight Flight or flying is the process by which an object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Entity, something that is tangible and within the grasp of the senses ** Object (abstract), an o ...
.


Skeletal system

The skeleton consists of very lightweight bones. They have large air-filled cavities (called pneumatic cavities) which connect with the
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertainment, and media * ''Network'' (1976 film), a 1976 Ame ...

respiratory system
. The skull bones in adults are fused and do not show
cranial sutures In anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of livi ...
. The orbital cavities that house the eyeballs are large and separated from each other by a bony
septum In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

septum
(partition). The has cervical, thoracic, lumbar and caudal regions with the number of cervical (neck) vertebrae highly variable and especially flexible, but movement is reduced in the anterior
thoracic vertebrae In vertebrates Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, c ...

thoracic vertebrae
and absent in the later vertebrae. The last few are fused with the
pelvis The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen The abdomen (colloquially called the belly, tummy, midriff or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in ...

pelvis
to form the
synsacrum The synsacrum is a skeletal structure of birds Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwi ...

synsacrum
. The ribs are flattened and the
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, human lung, lungs, and major blood vessels from in ...

sternum
is keeled for the attachment of flight muscles except in the flightless bird orders. The forelimbs are modified into wings. The wings are more or less developed depending on the species; the only known groups that lost their wings are the
extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...
moa Moa (order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such ...

moa
and
elephant bird Elephant birds are members of the extinct Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bi ...

elephant bird
s.


Excretory system

Like the
reptile Reptiles, as most commonly defined, are the animals in the class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or ...

reptile
s, birds are primarily uricotelic, that is, their
kidney The kidneys are two reddish-brown bean-shaped organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized ...

kidney
s extract
nitrogenous waste Metabolic wastes or excrements are substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything ...
from their bloodstream and excrete it as
uric acid Uric acid is a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of orga ...

uric acid
, instead of
urea Urea, also known as carbamide, is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the prop ...

urea
or
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct ch ...

ammonia
, through the ureters into the intestine. Birds do not have a
urinary bladder The urinary bladder, or simply bladder, is a hollow Muscle, muscular organ in humans and other vertebrates that stores urine from the kidneys before disposal by urination. In humans the bladder is a hollow distensible organ that sits on the pel ...
or external urethral opening and (with exception of the
ostrich ''Struthio'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circums ...

ostrich
) uric acid is excreted along with faeces as a semisolid waste. However, birds such as hummingbirds can be facultatively ammonotelic, excreting most of the nitrogenous wastes as ammonia. They also excrete
creatine Creatine ( or ) is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, ...

creatine
, rather than
creatinine Creatinine ( or ; from el, κρέας, kreas, flesh) is a breakdown product of creatine phosphate Phosphocreatine, also known as creatine phosphate (CP) or PCr (Pcr), is a phosphorylated creatine molecule that serves as a rapidly mobilizable ...

creatinine
like mammals. This material, as well as the output of the intestines, emerges from the bird's
cloaca In animal anatomy, a cloaca (plural cloacae or ) is the posterior orifice An orifice is any opening, mouth, hole or vent, as in a pipe, a plate, or a body * Body orifice, any opening in the body of a human or animal *Orifice plate, a restric ...

cloaca
. The cloaca is a multi-purpose opening: waste is expelled through it, most birds mate by , and females lay eggs from it. In addition, many species of birds regurgitate pellets. It is a common but not universal feature of
altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents develop in spurts after birth. The word is derived from the Latin Latin (, or , ) is a classical languag ...
passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), bi ...
nestlings (born helpless, under constant parental care) that instead of excreting directly into the nest, they produce a
fecal sac File:Sialia mexicana -Los Osos -California -removing fecal sac from nestbox-8.jpg, alt=A blue bird with a small white object in its beak flies against a green background., Many species, such as the western bluebird, carry fecal sacs some distance f ...
. This is a mucus-covered pouch that allows parents to either dispose of the waste outside the nest or to recycle the waste through their own digestive system.


Reproductive system

Males within
Palaeognathae Palaeognathae (; ) is a clade of birds, called paleognaths, within the subclass Neornithes of the class (biology), class Aves. It is one of the two extant taxon, extant infraclasses of birds, the other being Neognathae, both of which form Neorni ...
(with the exception of the
kiwi KIWI (102.9 FM, "Radio Lobo") is a commercial radio station , Sweden , Norway Radio broadcasting is transmission of audio signal, audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestria ...
s), the
Anseriformes Anseriformes is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, ...

Anseriformes
(with the exception of
screamer The screamers are three South American bird species placed in Family (biology), family Anhimidae. They were thought to be related to the Galliformes because of similar beak, bills, but are more related to ducks (family Anatidae),Todd, F. (1991) ...

screamer
s), and in rudimentary forms in
Galliformes Galliformes is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, ...

Galliformes
(but fully developed in
Cracidae The chachalacas, guans and curassows are bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwid ...
) possess a
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during Copulation (zoology), copulation. Such organs occur in many animals, both #Vertebrates, vertebrate ...
, which is never present in
Neoaves Neoaves is a clade that consists of all modern Bird, birds (Neornithes or Aves) with the exception of Paleognathae (ratites and kin) and Galloanserae (ducks, chickens and kin). Almost 95% of the roughly 10,000 known species of modern birds belong ...
. The length is thought to be related to
sperm competition Sperm competition is the competitive process between spermatozoa A spermatozoon (pronounced , alternate spelling spermatozoön; plural spermatozoa; from grc, σπέρμα ("seed") and grc, ζῷον ("living being")) is a motile Motilit ...
. When not copulating, it is hidden within the
proctodeum A proctodeum is the back ectodermal The ectoderm is one of the three primary germ layer A germ layer is a primary layer of cells that forms during embryonic development. The three germ layers in vertebrate Vertebrates () comprise all speci ...
compartment within the cloaca, just inside the vent. Female birds have sperm storage tubules that allow sperm to remain viable long after copulation, a hundred days in some species. Sperm from multiple males may
compete Competition arises whenever two or more parties strive for a common goal which cannot be shared: where one's gain is the other's loss (an example of which is a zero-sum game). Competition includes rivalry between entities such as organisms, ind ...
through this mechanism. Most female birds have a single
ovary The ovary is an organ found in the female reproductive system The female reproductive system is made up of the internal and external sex organs that function in reproduction of new offspring. In humans, the female reproductive system is im ...

ovary
and a single
oviduct The oviduct is the passageway in animals from an ovary The ovary is an organ found in the female reproductive system The female reproductive system is made up of the internal and external sex organs that function in reproduction of new of ...
, both on the left side, but there are exceptions: species in at least 16 different orders of birds have two ovaries. Even these species, however, tend to have a single oviduct. It has been speculated that this might be an adaptation to flight, but males have two testes, and it is also observed that the gonads in both sexes decrease dramatically in size outside the breeding season. Also terrestrial birds generally have a single ovary, as does the
platypus The platypus (''Ornithorhynchus anatinus''), sometimes referred to as the duck-billed platypus, is a List of semiaquatic tetrapods, semiaquatic, egg-laying mammal Endemic (ecology), endemic to Eastern states of Australia, eastern Australia, ...

platypus
, an egg-laying mammal. A more likely explanation is that the egg develops a shell while passing through the oviduct over a period of about a day, so that if two eggs were to develop at the same time, there would be a risk to survival. Birds have two sexes: either
female Female (symbol: ♀) is the sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of ...

female
or
male Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilization. A male organism cannot sexual reproduction, reproduce sexually ...

male
. The sex of birds is determined by the Z and W sex chromosomes, rather than by the X and Y chromosomes present in
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s. Male birds have two Z chromosomes (ZZ), and female birds have a W chromosome and a Z chromosome (WZ). In nearly all species of birds, an individual's sex is determined at fertilisation. However, one recent study claimed to demonstrate
temperature-dependent sex determination Temperature-dependent sex determination (TSD) is a type of environmental sex determination Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after ...
among the
Australian brushturkey The Australian brushturkey or Australian brush-turkey or gweela (''Alectura lathami''), also frequently called the scrub turkey or bush turkey, is a common, widespread species of mound-building bird from the family In human society, family ...
, for which higher temperatures during incubation resulted in a higher female-to-male
sex ratio The sex ratio is the ratio In mathematics, a ratio indicates how many times one number contains another. For example, if there are eight oranges and six lemons in a bowl of fruit, then the ratio of oranges to lemons is eight to six (that is, ...
. This, however, was later proven to not be the case. These birds do not exhibit temperature-dependent sex determination, but temperature-dependent sex mortality.


Respiratory and circulatory systems

Birds have one of the most complex
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertainment, and media * ''Network'' (1976 film), a 1976 Ame ...

respiratory system
s of all animal groups. Upon inhalation, 75% of the fresh air bypasses the lungs and flows directly into a posterior
air sac Air sacs are spaces within an organism where there is the constant presence of air. Among modern animals, birds possess the most air sacs (9–11), with their extinct dinosaurian relatives showing a great increase in the pneumatization (presence o ...
which extends from the lungs and connects with air spaces in the bones and fills them with air. The other 25% of the air goes directly into the lungs. When the bird exhales, the used air flows out of the lungs and the stored fresh air from the posterior air sac is simultaneously forced into the lungs. Thus, a bird's lungs receive a constant supply of fresh air during both inhalation and exhalation. Sound production is achieved using the
syrinx In classical Greek mythology Greek mythology is the body of myth Myth is a folklore genre Folklore is the expressive body of culture shared by a particular group of people; it encompasses the tradition A tradition is a belief ...
, a muscular chamber incorporating multiple tympanic membranes which diverges from the lower end of the trachea; the trachea being elongated in some species, increasing the volume of vocalisations and the perception of the bird's size. In birds, the main arteries taking blood away from the heart originate from the right
aortic arch The aortic arch, arch of the aorta, or transverse aortic arch () is the part of the aorta The aorta ( ) is the main and largest in the , originating from the of the and extending down to the , where it into two smaller arteries (the ). T ...
(or pharyngeal arch), unlike in the mammals where the left aortic arch forms this part of the
aorta The aorta ( ) is the main and largest artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vas ...

aorta
. The postcava receives blood from the limbs via the renal portal system. Unlike in mammals, the circulating
red blood cells Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...

red blood cells
in birds retain their
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nucleus
.


Heart type and features

The avian circulatory system is driven by a four-chambered, myogenic heart contained in a fibrous pericardial sac. This pericardial sac is filled with a
serous fluid In physiology Physiology (; ) is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in ...
for lubrication.Whittow, G. (2000). Sturkie's Avian Physiology/ edited by G. Causey Whittow. San Diego : Academic Press, 2000. The heart itself is divided into a right and left half, each with an atrium and ventricle. The atrium and ventricles of each side are separated by atrioventricular valves which prevent back flow from one chamber to the next during contraction. Being myogenic, the heart's pace is maintained by pacemaker cells found in the sinoatrial node, located on the right atrium. The
sinoatrial node The sinoatrial node (also known as the sinuatrial node, SA node or sinus node) is a group of Cell (biology), cells known as pacemaker cells, located in the wall of the atrium (heart), right atrium of the heart. These cells can produce an electric ...
uses calcium to cause a depolarising
signal transduction pathway Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation residue Protein phosphorylation is a reversible post-translational ...
from the atrium through right and left atrioventricular bundle which communicates contraction to the ventricles. The avian heart also consists of muscular arches that are made up of thick bundles of muscular layers. Much like a mammalian heart, the avian heart is composed of
endocardial The endocardium is the innermost layer of tissue that lines the chambers of the heart The heart is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly know ...
,
myocardial Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism ...
and epicardial layers. The atrium walls tend to be thinner than the ventricle walls, due to the intense ventricular contraction used to pump oxygenated blood throughout the body. Avian hearts are generally larger than mammalian hearts when compared to body mass. This adaptation allows more blood to be pumped to meet the high metabolic need associated with flight.Hoagstrom, C.W. (2002). "Vertebrate Circulation". ''Magill's Encyclopedia of Science: Animal Life''. Vol 1, pp. 217–219. Pasadena, California, Salem Press.


Organisation

Birds have a very efficient system for diffusing oxygen into the blood; birds have a ten times greater surface area to
gas exchange Gas exchange is the physical process by which gases move passively by Diffusion#Diffusion vs. bulk flow, diffusion across a surface. For example, this surface might be the air/water interface of a water body, the surface of a gas bubble in a liqui ...

gas exchange
volume than mammals. As a result, birds have more blood in their capillaries per unit of volume of lung than a mammal. The arteries are composed of thick elastic muscles to withstand the pressure of the ventricular contractions, and become more rigid as they move away from the heart. Blood moves through the arteries, which undergo
vasoconstriction Vasoconstriction is the narrowing of the blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of th ...

vasoconstriction
, and into arterioles which act as a transportation system to distribute primarily oxygen as well as nutrients to all tissues of the body.Hill, Richard W. (2012) Animal Physiology/ Richard W. Hill, Gordon A. Wyse, Margaret Anderson. Third Edition pp. 647–678. Sinauer Associates, Sunderland, MA As the arterioles move away from the heart and into individual organs and tissues they are further divided to increase surface area and slow blood flow. Blood travels through the arterioles and moves into the capillaries where gas exchange can occur. Capillaries are organised into capillary beds in tissues; it is here that blood exchanges oxygen for carbon dioxide waste. In the capillary beds, blood flow is slowed to allow maximum
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration In chemistry Chemistry is the study of the properties and behavior of . It is a that covers ...

diffusion
of oxygen into the tissues. Once the blood has become deoxygenated, it travels through venules then veins and back to the heart. Veins, unlike arteries, are thin and rigid as they do not need to withstand extreme pressure. As blood travels through the venules to the veins a funneling occurs called
vasodilation Vasodilation is the widening of blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is ...

vasodilation
bringing blood back to the heart. Once the blood reaches the heart, it moves first into the right atrium, then the right ventricle to be pumped through the lungs for further gas exchange of carbon dioxide waste for oxygen. Oxygenated blood then flows from the lungs through the left atrium to the left ventricle where it is pumped out to the body.


Nervous system

The
nervous system In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mecha ...

nervous system
is large relative to the bird's size. The most developed part of the brain is the one that controls the flight-related functions, while the
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain The hindbrain or rhombencephalon is a developmental Development of the human body is the process of growth to maturity. The process begins with fertilization ...

cerebellum
coordinates movement and the
cerebrum The cerebrum, telencephalon or endbrain, is the largest part of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal l ...
controls behaviour patterns, navigation, mating and
nest A nest is a structure built for certain animals to hold eggs Eggs are laid by female animals of many different species, including bird egg, birds, reptiles, amphibians, a few monotreme, mammals, and fish, and many of these have been eaten ...

nest
building. Most birds have a poor
sense of smell The sense of smell, or olfaction, is the special sense In medicine Medicine is the Art (skill), art, science, and Praxis (process) , practice of caring for a patient and managing the diagnosis, prognosis, Preventive medicine, prevention, the ...
with notable exceptions including
kiwi KIWI (102.9 FM, "Radio Lobo") is a commercial radio station , Sweden , Norway Radio broadcasting is transmission of audio signal, audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestria ...
s,
New World vulture The New World vulture or condor family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territ ...
s and tubenoses. The avian
visual system The visual system comprises the sensory organ A sense is a biological system A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined b ...
is usually highly developed. Water birds have special flexible lenses, allowing accommodation for vision in air and water. Some species also have dual fovea. Birds are tetrachromatic, possessing
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
(UV) sensitive
cone cell Cone cells, or cones, are photoreceptor cells A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina The retina (from la, rete) is the innermost, light-sensitive layer of tissue of the eye of most ve ...

cone cell
s in the eye as well as green, red and blue ones. They also have double cones, likely to mediate achromatic vision. Many birds show plumage patterns in
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
that are invisible to the human eye; some birds whose sexes appear similar to the naked eye are distinguished by the presence of ultraviolet reflective patches on their feathers. Male
blue tit The Eurasian blue tit (''Cyanistes caeruleus'') is a small passerine A passerine is any bird of the Order (biology), order Passeriformes (, Latin ''passer'' (“sparrow”) + ''formis'' (“-shaped”)), which includes more than half of all ...

blue tit
s have an ultraviolet reflective crown patch which is displayed in courtship by posturing and raising of their nape feathers. Ultraviolet light is also used in foraging—
kestrel The name kestrel (from french: crécerelle, derivative from , i.e. ratchet) is given to several members of the falcon genus, ''Falco''. Kestrels are most easily distinguished by their typical hunting behaviour which is to hover at a height of ar ...

kestrel
s have been shown to search for prey by detecting the UV reflective urine trail marks left on the ground by rodents. With the exception of pigeons and a few other species, the eyelids of birds are not used in blinking. Instead the eye is lubricated by the
nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent In the field of optics Optics is the branch of physics Physics is the that studies , its , its and behavior through , and the related e ...
, a third eyelid that moves horizontally. The nictitating membrane also covers the eye and acts as a
contact lens Contact lenses, or simply contacts, are thin lenses A lens is a transmissive optics, optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while ...

contact lens
in many aquatic birds. The bird
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well ...

retina
has a fan shaped blood supply system called the pecten. Eyes of most birds are large, not very round and capable of only limited movement in the orbits, typically 10-20°. Birds with eyes on the sides of their heads have a wide
visual field The visual field is the "spatial array of visual sensations available to observation in introspection Introspection is the examination of one's own conscious thoughts and feelings. In psychology, the process of introspection relies on the observ ...
, while birds with eyes on the front of their heads, such as owls, have
binocular vision Binocular may refer to: Science and technology * Binocular vision In , binocular vision is a type of in which an animal has two s capable of facing the same direction to perceive a single of its surroundings. Neurological researcher Manfred ...

binocular vision
and can estimate the
depth of field For many cameras, depth of field (DOF) is the distance between the nearest and the farthest objects that are in acceptably sharp focus in an image. The depth of field can be calculated based on focal length The focal length of an optical ...

depth of field
. The avian
ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists ...

ear
lacks external
pinnae The auricle or auricula is the visible part of the ear that is outside the head. It is also called the pinna (Latin for "wing" or "fin", plural pinnae), a term that is used more in zoology. Structure The diagram shows the shape and location of m ...
but is covered by feathers, although in some birds, such as the ''
Asio ''Asio'' is a genus of typical owls The true owls or typical owls (family (biology), family Strigidae) are one of the two generally accepted families of owls, the other being the Barn-owl, barn owls (Tytonidae). The Sibley-Ahlquist taxonomy u ...
'', ''
Bubo A bubo (Greek βουβών, ''boubṓn'', 'groin') is adenitis Adenitis is a general term for an inflammation of a gland. Often it is used to refer to lymphadenitis which is the inflammation of a lymph node. Classification Lymph node adenitis ...
'' and ''
Otus Otus may refer to: * Otus (education), a K-12 educational technology company * HMS Otus, HMS ''Otus'', two ships in the Royal Navy * Otus (bird), ''Otus'' (bird), genus of owls * Otus (mythology), giant in Greek mythology, brother of Ephialtes, on ...
''
owl Owls are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological k ...

owl
s, these feathers form tufts which resemble ears. The
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear T ...

inner ear
has a
cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opene ...

cochlea
, but it is not spiral as in mammals.


Defence and intraspecific combat

A few species are able to use chemical defences against predators; some
Procellariiformes Procellariiformes is an order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or ...
can eject an unpleasant
stomach oil Stomach oil is the light oil composed of neutral dietary lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biolo ...
against an aggressor, and some species of
pitohui The pitohuis are bird species endemic Endemism is the state of a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A spec ...
s from
New Guinea New Guinea (; Hiri Motu Hiri Motu, also known as Police Motu, Pidgin Motu, or just Hiri, is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign ...

New Guinea
have a powerful
neurotoxin Neurotoxins are toxin A toxin is a harmful substance produced within living cells or organisms; synthetic toxicants created by artificial processes are thus excluded. The term was first used by organic chemist Ludwig Brieger (1849–1919), d ...
in their skin and feathers. A lack of field observations limit our knowledge, but intraspecific conflicts are known to sometimes result in injury or death. The screamers ( Anhimidae), some jacanas ('' Jacana'', '' Hydrophasianus''), the spur-winged goose ('' Plectropterus''), the torrent duck (''
Merganetta The torrent duck (''Merganetta armata'') is a member of the duck Duck is the common name for numerous species in the waterfowl family (biology), family Anatidae which also includes swans and goose, geese. Ducks are divided among several subf ...
'') and nine species of lapwing (''
Vanellus ''Vanellus'' is the genus of wader 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, wade in order to foraging, forage for food (s ...
'') use a sharp spur on the wing as a weapon. The steamer ducks (''
Tachyeres The steamer ducks are a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refe ...
''), geese and swans (''
Anserinae The Anserinae are a subfamily in the waterfowl family Anatidae. It includes the swans and true Goose, geese. Under alternative systematics, systematical concepts (see e.g., Terres & NAS, 1991), it is split into two subfamilies, the Anserinae con ...
''), the solitaire (''''), sheathbills (''
Chionis The sheathbills are a family (biology), family of birds, Chionidae. Classified in the wader order Charadriiformes, the family contains one genus, ''Chionis'', with only two species. They breed on subantarctic islands and the Antarctic Peninsula, ...
''), some guans (''
Crax ''Crax'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscrib ...
'') and stone curlews (''
Burhinus ''Burhinus'' is a genus of bird in the family Burhinidae. This family also contains the genus ''Esacus.''del Hoyo J, Elliott A, Sargatal J (1996) ''Handbook of the Birds of the World'', ''vol 3.'' Lynx, Barcelona The genus name ''Burhinus'' comes ...
'') use a bony knob on the
alula The alula , or bastard wing, (plural ''alulae'') is a small projection on the anterior edge of the wing of modern birds and a few non-avian dinosaurs. The word is Latin and means "winglet"; it is the diminutive of ''ala'', meaning "wing". The alu ...

alula
r metacarpal to punch and hammer opponents. The jacanas '' Actophilornis'' and '' Irediparra'' have an expanded, blade-like radius. The extinct '' Xenicibis'' was unique in having an elongate forelimb and massive hand which likely functioned in combat or defence as a jointed club or flail.
Swans Swans are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kin ...

Swans
, for instance, may strike with the bony spurs and bite when defending eggs or young.


Feathers, plumage, and scales

Feathers are a feature characteristic of birds (though also present in some dinosaurs not currently considered to be true birds). They facilitate
flight Flight or flying is the process by which an object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Entity, something that is tangible and within the grasp of the senses ** Object (abstract), an o ...
, provide insulation that aids in
thermoregulation Thermoregulation is the ability of an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxo ...
, and are used in display, camouflage, and signalling. There are several types of feathers, each serving its own set of purposes. Feathers are epidermal growths attached to the skin and arise only in specific tracts of skin called pterylae. The distribution pattern of these feather tracts (pterylosis) is used in taxonomy and systematics. The arrangement and appearance of feathers on the body, called
plumage Plumage ( "feather") is a layer of feather Feathers are epidermal growths that form a distinctive outer covering, or plumage Plumage ( "feather") is a layer of feather Feathers are epidermal growths that form a distinctive outer ...
, may vary within species by age,
social status Social status is the level of social value a person is considered to hold. More specifically, it refers to the relative level of respect, honour Honour (British English British English (BrE) is the standard dialect of the English langu ...
, and
sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot sexual r ...
. Plumage is regularly
moult In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

moult
ed; the standard plumage of a bird that has moulted after breeding is known as the "" plumage, or—in the
Humphrey–Parkes terminology Humphrey–Parkes terminology is a system of nomenclature for the plumage of birds. Before the Humphrey–Parkes system, plumage was named after the belief that a certain plumage was breeding plumage and others were not. However, as this system did ...
—"basic" plumage; breeding plumages or variations of the basic plumage are known under the Humphrey–Parkes system as "" plumages. Moulting is annual in most species, although some may have two moults a year, and large birds of prey may moult only once every few years. Moulting patterns vary across species. In passerines,
flight feather Flight feathers (''Pennae volatus'') are the long, stiff, asymmetrically shaped, but symmetrically paired pennaceous feather The pennaceous feather is a type of feather Feathers are epidermal growths that form a distinctive outer coveri ...
s are replaced one at a time with the innermost being the first. When the fifth of sixth primary is replaced, the outermost begin to drop. After the innermost tertiaries are moulted, the starting from the innermost begin to drop and this proceeds to the outer feathers (centrifugal moult). The greater primary are moulted in synchrony with the primary that they overlap. A small number of species, such as ducks and geese, lose all of their flight feathers at once, temporarily becoming flightless.de Beer SJ, Lockwood GM, Raijmakers JHFS, Raijmakers JMH, Scott WA, Oschadleus HD, Underhill LG (2001).
SAFRING Bird Ringing Manual
".
As a general rule, the tail feathers are moulted and replaced starting with the innermost pair. Centripetal moults of tail feathers are however seen in the
Phasianidae The Phasianidae are a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of soci ...

Phasianidae
. The centrifugal moult is modified in the tail feathers of
woodpecker Woodpeckers are part of the Family (biology), family Picidae, which also includes the piculets, wrynecks, and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the extreme pol ...

woodpecker
s and
treecreeper The treecreepers are a family (biology), family, Certhiidae, of small passerine Aves, birds, widespread in wooded regions of the Northern Hemisphere and sub-Saharan Africa. The family contains ten species in two genus, genera, ''Certhia'' and ''Sa ...

treecreeper
s, in that it begins with the second innermost pair of feathers and finishes with the central pair of feathers so that the bird maintains a functional climbing tail. The general pattern seen in
passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), bi ...
s is that the primaries are replaced outward, secondaries inward, and the tail from centre outward. Before nesting, the females of most bird species gain a bare
brood patch A brood patch is a patch of featherless skin on the underside of birds during the nesting season. Feathers act as inherent insulators, and prevent efficient incubation. Birds have solved this evolutionary dilemma by developing dedicated brood patch ...
by losing feathers close to the belly. The skin there is well supplied with blood vessels and helps the bird in incubation. Feathers require maintenance and birds preen or groom them daily, spending an average of around 9% of their daily time on this. The bill is used to brush away foreign particles and to apply
wax Waxes are a diverse class of organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prope ...
y secretions from the
uropygial gland The uropygial gland, informally known as the preen gland or the oil gland, is a bilobed sebaceous gland A sebaceous gland is a microscopic exocrine gland A gland is a group of cells in an animal's body that synthesizes substances (such as hor ...
; these secretions protect the feathers' flexibility and act as an antimicrobial agent, inhibiting the growth of feather-degrading
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
. This may be supplemented with the secretions of
formic acid Formic acid, systematically named methanoic acid, is the simplest carboxylic acid A carboxylic acid is an organic acid An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acid ...

formic acid
from ants, which birds receive through a behaviour known as
anting Anting () is a town in Jiading District, Shanghai, bordering Kunshan, Jiangsu to the west. It has 96,000 inhabitants and, after the July 2009 merger of Huangdu (), an area of .
, to remove feather parasites. The
scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory) In the mathematical discipline of descriptive set theory, a scale is a certain kind of object defined on a set (mathematics), set of point (mathematics), points in some Po ...

scales
of birds are composed of the same keratin as beaks, claws, and spurs. They are found mainly on the toes and
metatarsus The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the Tarsus (skeleton), tarsal bones of the hind- and mid-foot and the Phalanges of the foot, phalanges of the toes. Lacking individual names, the met ...

metatarsus
, but may be found further up on the ankle in some birds. Most bird scales do not overlap significantly, except in the cases of
kingfisher Kingfishers or Alcedinidae are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or soc ...

kingfisher
s and
woodpecker Woodpeckers are part of the Family (biology), family Picidae, which also includes the piculets, wrynecks, and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the extreme pol ...

woodpecker
s. The scales of birds are thought to be homologous to those of reptiles and mammals.


Flight

Most birds can
fly Flies are insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning ...
, which distinguishes them from almost all other vertebrate classes. Flight is the primary means of locomotion for most bird species and is used for searching for food and for escaping from predators. Birds have various adaptations for flight, including a lightweight skeleton, two large flight muscles, the pectoralis (which accounts for 15% of the total mass of the bird) and the supracoracoideus, as well as a modified forelimb (
wing A wing is a type of fin A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust Thrust is a reaction (physics), reaction force (physics), force describ ...

wing
) that serves as an
aerofoil An airfoil (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American English ...

aerofoil
. Wing shape and size generally determine a bird's flight style and performance; many birds combine powered, flapping flight with less energy-intensive soaring flight. About 60 extant bird species are
flightless s are a well-known example of flightless birds. Flightless birds are birds that through evolution lost the ability to flight, fly. There are over 60 extant species, including the well known ratites (ostriches, emu, cassowary, cassowaries, Rhea ( ...
, as were many extinct birds. Flightlessness often arises in birds on isolated islands, probably due to limited resources and the absence of land predators. Although flightless, penguins use similar musculature and movements to "fly" through the water, as do some flight-capable birds such as
auk An auk or alcid is a bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabo ...
s,
shearwater Shearwaters are medium-sized long-winged seabird Seabirds (also known as marine birds) are bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chamb ...
s and
dipper Dippers are members of the genus ''Cinclus'' in the bird family Cinclidae, so-called because of their bobbing or dipping movements. They are unique among passerines for their ability to dive and swim underwater. Taxonomy The genus ''Cinclus'' ...

dipper
s.


Behaviour

Most birds are
diurnal Diurnal ("daily Daily or The Daily may refer to: Journalism * Daily newspaper A newspaper is a Periodical literature, periodical publication containing written News, information about current events and is often typed in black ink with a ...
, but some birds, such as many species of
owl Owls are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological k ...

owl
s and
nightjar Nightjars are medium-sized nocturnal or crepuscular birds in the family (biology), family Caprimulgidae and Order (biology), order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called goatsu ...
s, are
nocturnal Nocturnality is an animal behavior Ethology is the scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was origina ...
or
crepuscular A crepuscular animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organis ...

crepuscular
(active during twilight hours), and many coastal
wader 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, wade in order to foraging, forage for food (such as insects or crustaceans) in the m ...
s feed when the tides are appropriate, by day or night.


Diet and feeding

are varied and often include
nectar Nectar is a sugar Sugar is the generic name for , soluble s, many of which are used in food. Simple sugars, also called s, include , , and . Compound sugars, also called s or double sugars, are molecules made of two monosaccharides jo ...
, fruit, plants, seeds,
carrion Carrion (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the R ...

carrion
, and various small animals, including other birds. The digestive system of birds is unique, with a
crop A crop is a plant that can be grown and harvested extensively for profit or subsistence. Crops may refer either to the harvested parts or to the harvest in a more refined state. Most crops are cultivated in agriculture Agriculture is th ...
for storage and a
gizzard The gizzard, also referred to as the ventriculus, gastric mill, and gigerium, is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rel ...

gizzard
that contains swallowed stones for grinding food to compensate for the lack of teeth. Most birds are highly adapted for rapid digestion to aid with flight. Some migratory birds have adapted to use protein stored in many parts of their bodies, including protein from the intestines, as additional energy during migration. (Erratum in ''Proceedings of the Royal Society B'' 267(1461):2567.) Birds that employ many strategies to obtain food or feed on a variety of food items are called generalists, while others that concentrate time and effort on specific food items or have a single strategy to obtain food are considered specialists. Avian foraging strategies can vary widely by species. Many birds
glean Gleaning is the act of collecting leftover crops from farmers' fields after they have been commercially harvested or on fields where it is not economically profitable to harvest. It is a practice described in the Hebrew Bible that became a legally ...
for insects, invertebrates, fruit, or seeds. Some hunt insects by suddenly attacking from a branch. Those species that seek
pest Pest or The Pest may refer to: Science and medicine * Pest (organism), an animal or plant detrimental to humans or human concerns ** Weed, a plant considered undesirable * Infectious disease, an illness resulting from an infection ** Plague (diseas ...
insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

insect
s are considered beneficial 'biological control agents' and their presence encouraged in
biological pest control Biological control or biocontrol is a method of controlling pests such as insect Insects (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was ...
programmes. Combined, insectivorous birds eat 400–500 million metric tons of arthropods annually. Nectar feeders such as
hummingbird Hummingbirds are Bird, birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With about 360 species, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropi ...

hummingbird
s,
sunbird Sunbirds and spiderhunters make up the family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or socia ...

sunbird
s, lories, and lorikeets amongst others have specially adapted brushy tongues and in many cases bills designed to fit
co-adaptedIn biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, De ...
flowers.
Kiwi KIWI (102.9 FM, "Radio Lobo") is a commercial radio station , Sweden , Norway Radio broadcasting is transmission of audio signal, audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestria ...
s and
shorebird FIle:Vadare - Ystad-2021.jpg, 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, wade in order to foraging, forage for food (such as ins ...

shorebird
s with long bills probe for invertebrates; shorebirds' varied bill lengths and feeding methods result in the separation of
ecological niche In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms ...

ecological niche
s.
Loon Loons (North America) or divers (United Kingdom / Ireland) are a group of aquatic bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicell ...

Loon
s,
diving duck The diving ducks, commonly called pochards or scaups, are a category of duck Duck is the common name for numerous species of waterfowl Anseriformes is an order of bird Birds are a group of warm-blooded vertebrates constituting ...
s,
penguin Penguins (order Order or ORDER or Orders may refer to: * Orderliness Orderliness is associated with other qualities such as cleanliness Cleanliness is both the abstract state of being clean and free from germs, dirt, trash, or waste, and t ...

penguin
s and
auks An auk or alcid is a bird of the family Alcidae in the order Charadriiformes. The alcid family includes the Uria, murres, guillemots, Aethia, auklets, puffins, and Brachyramphus, murrelets. The word ''auk'' is derived from Icelandic language, ...

auks
pursue their prey underwater, using their wings or feet for propulsion, while aerial predators such as sulids,
kingfisher Kingfishers or Alcedinidae are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or soc ...

kingfisher
s and
tern Terns are seabird Seabirds (also known as marine birds) are bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet ligh ...

tern
s plunge dive after their prey.
Flamingo Flamingos or flamingoes are a type of wading bird FIle:Vadare - Ystad-2021.jpg, 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, ...

Flamingo
s, three species of
prion Prions are misfolded protein Protein folding is the physical process Physical changes are changes affecting the form of a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matte ...
, and some ducks are
filter feeder Filter feeders are a sub-group of suspension feeding animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consu ...
s.
Geese A goose (plural geese) is a bird of any of several waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and An ...

Geese
and
dabbling duck The Anatinae are a subfamily In biological classification In biology, taxonomy () is the scientific study of naming, defining (Circumscription (taxonomy), circumscribing) and classifying groups of biological organisms based on shared cha ...
s are primarily grazers. Some species, including
frigatebird Frigatebirds (also listed as "frigate bird", "frigate-bird", "frigate", "frigate-petrel") are a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, ...
s,
gull Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns (family Sternidae) and only distantly related to auks, Skimmer (bird), skimmers and even more distantly to wade ...

gull
s, and
skua The skuas are a group of predatory seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrates constituting the class Class or The Class may refer to: Common uses not otherwise categ ...

skua
s, engage in
kleptoparasitism Kleptoparasitism (etymologically, parasitism Parasitism is a close relationship between species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioche ...
, stealing food items from other birds. Kleptoparasitism is thought to be a supplement to food obtained by hunting, rather than a significant part of any species' diet; a study of
great frigatebird The great frigatebird (''Fregata minor'') is a large seabird in the frigatebird family (biology), family. There are major nesting populations in the tropical Pacific (including the Galapagos Islands) and Indian Oceans, as well as a tiny populatio ...
s stealing from estimated that the frigatebirds stole at most 40% of their food and on average stole only 5%. Other birds are
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study ...
s; some of these, like
vulture A vulture is a bird of prey Birds of prey, also known as raptors, include species of bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , an ...

vulture
s, are specialised carrion eaters, while others, like gulls,
corvid Corvidae is a cosmopolitan family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to main ...
s, or other birds of prey, are opportunists.


Water and drinking

Water is needed by many birds although their mode of excretion and lack of
sweat gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of an ...
s reduces the physiological demands. Some desert birds can obtain their water needs entirely from moisture in their food. They may also have other adaptations such as allowing their body temperature to rise, saving on moisture loss from evaporative cooling or panting. Seabirds can drink seawater and have
salt gland The salt gland is an organ for excreting excess salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its natural form as a crystallinity ...

salt gland
s inside the head that eliminate excess salt out of the nostrils. Most birds scoop water in their beaks and raise their head to let water run down the throat. Some species, especially of arid zones, belonging to the
pigeon Columbidae () is a bird family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and o ...

pigeon
,
finch The true finches are small to medium-sized passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular ...
,
mousebird The mousebirds are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biolog ...
, button-quail and
bustard Bustards, including floricans and korhaans, are large, terrestrial Terrestrial refers to things related to land Land is the solid surface of the Earth that is not permanently covered by water. The vast majority of human activity throughou ...
families are capable of sucking up water without the need to tilt back their heads. Some desert birds depend on water sources and
sandgrouse Sandgrouse is the common name for Pteroclidae , a family (biology), family of sixteen species of bird, members of the order Pterocliformes . They are traditionally placed in two Genus, genera. The two central Asian species are classified as ''Syr ...

sandgrouse
are particularly well known for their daily congregations at waterholes. Nesting sandgrouse and many plovers carry water to their young by wetting their belly feathers. Some birds carry water for chicks at the nest in their crop or regurgitate it along with food. The pigeon family, flamingos and penguins have adaptations to produce a nutritive fluid called
crop milk A greater flamingo chick in Zoo Basel is fed crop milk">Zoo_Basel.html" ;"title="greater flamingo chick in Zoo Basel">greater flamingo chick in Zoo Basel is fed crop milk Crop milk is a secretion from the lining of the Crop (anatomy), crop of pare ...
that they provide to their chicks.


Feather care

Feathers, being critical to the survival of a bird, require maintenance. Apart from physical wear and tear, feathers face the onslaught of fungi, ectoparasitic feather mites and bird lice. The physical condition of feathers are maintained by often with the application of secretions from the . Birds also bathe in water or dust themselves. While some birds dip into shallow water, more aerial species may make aerial dips into water and arboreal species often make use of dew or rain that collect on leaves. Birds of arid regions make use of loose soil to dust-bathe. A behaviour termed as
anting Anting () is a town in Jiading District, Shanghai, bordering Kunshan, Jiangsu to the west. It has 96,000 inhabitants and, after the July 2009 merger of Huangdu (), an area of .
in which the bird encourages ants to run through their plumage is also thought to help them reduce the ectoparasite load in feathers. Many species will spread out their wings and expose them to direct sunlight and this too is thought to help in reducing fungal and ectoparasitic activity that may lead to feather damage.


Migration

Many bird species migrate to take advantage of global differences of
season A season is a division of the year based on changes in weather Weather is the state of the atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or ...

season
al temperatures, therefore optimising availability of food sources and breeding habitat. These migrations vary among the different groups. Many landbirds,
shorebird FIle:Vadare - Ystad-2021.jpg, 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, wade in order to foraging, forage for food (such as ins ...

shorebird
s, and
waterbird A water bird, alternatively waterbird or aquatic bird, is a bird that lives on or around water. In some definitions, the term ''water bird'' is especially applied to birds in freshwater ecosystem Fresh water (or freshwater) is any naturally ...

waterbird
s undertake annual long-distance migrations, usually triggered by the length of daylight as well as weather conditions. These birds are characterised by a breeding season spent in the
temperate In geography Geography (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its populati ...
or
polar region The Polar Regions, also called the frigid zones Zone or The Zone may refer to: Places Climate and altitude zones * Death zone (originally the lethal zone), altitudes above a certain point where the amount of oxygen is insufficient to sustain ...
s and a non-breeding season in the
tropical The tropics are the region of Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% ...

tropical
regions or opposite hemisphere. Before migration, birds substantially increase body fats and reserves and reduce the size of some of their organs. (Erratum in ''Proceedings of the Royal Society B'' 267(1461):2567.) Migration is highly demanding energetically, particularly as birds need to cross deserts and oceans without refuelling. Landbirds have a flight range of around and shorebirds can fly up to , although the
bar-tailed godwit The bar-tailed godwit (''Limosa lapponica'') is a large wader Waders or shorebirds are bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws ...

bar-tailed godwit
is capable of non-stop flights of up to .
Seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

Seabird
s also undertake long migrations, the longest annual migration being those of
sooty shearwater The sooty shearwater (''Ardenna grisea'') is a medium-large shearwater in the seabird family Procellariidae. ''Ardenna'' was first used to refer to a seabird by Italian naturalist Ulisse Aldrovandi in 1603, and ''grisea'' is medieval Latin for "g ...
s, which nest in
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
and
Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern ...

Chile
and spend the northern summer feeding in the North Pacific off Japan,
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, Anáaski) is a U.S. state in the Western United States, on the northwest extremity of the country's West Coast of the United State ...

Alaska
and
California California is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper i ...

California
, an annual round trip of . Other seabirds disperse after breeding, travelling widely but having no set migration route.
Albatross Albatrosses are very large Seabird, seabirds in the family (biology), family Diomedeidae. They range widely in the Southern Ocean and the North Pacific Ocean, Pacific. They are absent from the North Atlantic Ocean, Atlantic, although fossil rem ...

Albatross
es nesting in the
Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean The ocean (also the sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or ...

Southern Ocean
often undertake circumpolar trips between breeding seasons. Some bird species undertake shorter migrations, travelling only as far as is required to avoid bad weather or obtain food. Irruptive species such as the boreal
finch The true finches are small to medium-sized passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular ...

finch
es are one such group and can commonly be found at a location in one year and absent the next. This type of migration is normally associated with food availability. Species may also travel shorter distances over part of their range, with individuals from higher latitudes travelling into the existing range of conspecifics; others undertake partial migrations, where only a fraction of the population, usually females and subdominant males, migrates. Partial migration can form a large percentage of the migration behaviour of birds in some regions; in Australia, surveys found that 44% of non-passerine birds and 32% of passerines were partially migratory.
Altitudinal migration Altitudinal migration is a short-distance animal migration Animal migration is the relatively long-distance movement of individual animals, usually on a seasonal basis. It is the most common form of Migration (ecology), migration in ecology. It i ...
is a form of short-distance migration in which birds spend the breeding season at higher altitudes and move to lower ones during suboptimal conditions. It is most often triggered by temperature changes and usually occurs when the normal territories also become inhospitable due to lack of food. Some species may also be nomadic, holding no fixed territory and moving according to weather and food availability.
Parrots Parrots, also known as psittacines , are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the K ...
as a
family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subject to the same Politic ...
are overwhelmingly neither migratory nor sedentary but considered to either be dispersive, irruptive, nomadic or undertake small and irregular migrations. The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a
Manx shearwater The Manx shearwater (''Puffinus puffinus'') is a medium-sized shearwater Shearwaters are medium-sized long-winged seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrates constituting t ...
released in
Boston Boston (, ), officially the City of Boston, is the capital city, capital and List of municipalities in Massachusetts, most populous city of the Commonwealth (U.S. state), Commonwealth of Massachusetts in the United States and 21st List of Unit ...

Boston
in the United States returned to its colony in
Skomer Skomer () or Skomer Island is an island off the coast of Pembrokeshire Pembrokeshire ( ; cy, Sir Benfro ) is a Local government in Wales#Principal areas, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshir ...
, in Wales within 13 days, a distance of . Birds navigate during migration using a variety of methods. For
diurnal Diurnal ("daily Daily or The Daily may refer to: Journalism * Daily newspaper A newspaper is a Periodical literature, periodical publication containing written News, information about current events and is often typed in black ink with a ...
migrants, the
sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

sun
is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock. Orientation with the stellar compass depends on the position of the
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived outline or pattern, typically representing an animal, mythological person or creature, or an inanimate object. The origins of the earliest ...

constellation
s surrounding
Polaris Polaris ( ), designated α Ursae Minoris ( Latinized to Alpha Ursae Minoris, abbreviated Alpha UMi, α UMi), commonly the North Star or Pole Star, is the brightest star of the constellation Ursa Minor. It is very close to the nort ...

Polaris
. These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised .


Communication

Birds
communicate Communication (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power o ...

communicate
using primarily visual and auditory signals. Signals can be interspecific (between species) and intraspecific (within species). Birds sometimes use plumage to assess and assert social dominance, to display breeding condition in sexually selected species, or to make threatening displays, as in the
sunbittern The sunbittern (''Eurypyga helias'') is a bittern Bitterns are birds belonging to the subfamily Botaurinae of the heron family Ardeidae. Bitterns tend to be shorter-necked and more secretive than other members of the family. They were call ...

sunbittern
's mimicry of a large predator to ward off
hawk Hawks are a group of medium- diurnal birds of prey Birds of prey, also known as raptors, include species of bird that primarily hunt and feed on vertebrates that are large relative to the hunter. Additionally, they have Bird vision, keen ey ...

hawk
s and protect young chicks. Variation in plumage also allows for the identification of birds, particularly between species. Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds. The most elaborate displays occur during courtship, where "dances" are often formed from complex combinations of many possible component movements; males' breeding success may depend on the quality of such displays. Bird calls and songs, which are produced in the
syrinx In classical Greek mythology Greek mythology is the body of myth Myth is a folklore genre Folklore is the expressive body of culture shared by a particular group of people; it encompasses the tradition A tradition is a belief ...
, are the major means by which birds communicate with
sound In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...

sound
. This communication can be very complex; some species can operate the two sides of the syrinx independently, allowing the simultaneous production of two different songs. Calls are used for a variety of purposes, including mate attraction, evaluation of potential mates, bond formation, the claiming and maintenance of territories, the identification of other individuals (such as when parents look for chicks in colonies or when mates reunite at the start of breeding season), and the warning of other birds of potential predators, sometimes with specific information about the nature of the threat. Some birds also use mechanical sounds for auditory communication. The ''
Coenocorypha The austral snipes, also known as the New Zealand snipes or tutukiwi, are a genus, ''Coenocorypha'', of tiny birds in the sandpiper family (biology), family, which are now only found on New Zealand outlying islands, New Zealand's outlying islands ...
''
snipe A snipe is any of about 26 wading bird FIle:Vadare - Ystad-2021.jpg, 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, wade in order ...

snipe
s of
New Zealand New Zealand ( mi, Aotearoa ''Aotearoa'' (; commonly pronounced by English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon Engl ...

New Zealand
drive air through their feathers,
woodpecker Woodpeckers are part of the Family (biology), family Picidae, which also includes the piculets, wrynecks, and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the extreme pol ...

woodpecker
s drum for long-distance communication, and
palm cockatoo The palm cockatoo (''Probosciger aterrimus''), also known as the goliath cockatoo or great black cockatoo, is a large smoky-grey or black Psittaciformes, parrot of the cockatoo family native to New Guinea, Aru Islands Regency, Aru Islands, and ...
s use tools to drum.


Flocking and other associations

While some birds are essentially territorial or live in small family groups, other birds may form large
flocks s Image:The flock of starlings acting as a swarm. - geograph.org.uk - 124593.jpg">200px, A swarm-like flock of flock, are foraging or in flight. Computer simulations and mathematical models which have been developed to emulate the flocking behavio ...
. The principal benefits of flocking are
safety in numbers Safety in numbers is the hypothesis that, by being part of a large physical group or mass, an individual is less likely to be the victim of a mishap, accident An accident is an unplanned event that sometimes has inconvenient or undesirable con ...
and increased foraging efficiency. Defence against predators is particularly important in closed habitats like forests, where
ambush predation Ambush predators or sit-and-wait predators are carnivorous animal A carnivore , meaning "meat eater" (Latin, ''caro'', genitive ''carnis'', meaning "meat" or "flesh" and ''vorare'' meaning "to devour"), is an organism, animal whose food and e ...
is common and multiple eyes can provide a valuable early warning system. This has led to the development of many
mixed-species feeding flock A mixed-species feeding flock, also termed a mixed-species foraging flock, mixed hunting party or informally bird wave, is a flock of usually insectivorous bird Birds are a group of warm-blooded vertebrates constituting the class (biology ...
s, which are usually composed of small numbers of many species; these flocks provide safety in numbers but increase potential competition for resources. Costs of flocking include bullying of socially subordinate birds by more dominant birds and the reduction of feeding efficiency in certain cases. Birds sometimes also form associations with non-avian species. Plunge-diving
seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

seabird
s associate with
dolphin Dolphin is the common name of aquatic mammal Aquatic and semiaquatic mammals are a diverse group of mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mam ...

dolphin
s and
tuna A tuna is a saltwater fish that belongs to the Tribe (biology), tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet ...

tuna
, which push shoaling fish towards the surface.
Hornbill The hornbills (Bucerotidae) are a family of bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shel ...

Hornbill
s have a mutualistic relationship with
dwarf mongoose The common dwarf mongoose (''Helogale parvula'') is a mongoose A mongoose is a small terrestrial carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat si ...

dwarf mongoose
s, in which they forage together and warn each other of nearby
birds of prey Birds of prey, also known as raptors, include species of bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Bi ...
and other predators.


Resting and roosting

The high metabolic rates of birds during the active part of the day is supplemented by rest at other times. Sleeping birds often use a type of sleep known as vigilant sleep, where periods of rest are interspersed with quick eye-opening "peeks", allowing them to be sensitive to disturbances and enable rapid escape from threats.
Swift The Society for Worldwide Interbank Financial Telecommunication (SWIFT), legally S.W.I.F.T. SCRL, is a Belgium, Belgian cooperative society that serves as an intermediary and executor of financial transactions between banks worldwide. It also ...
s are believed to be able to sleep in flight and radar observations suggest that they orient themselves to face the wind in their roosting flight. It has been suggested that there may be certain kinds of sleep which are possible even when in flight. Some birds have also demonstrated the capacity to fall into
slow-wave sleep Slow-wave sleep (SWS), often referred to as deep sleep, consists of stage three of non-rapid eye movement sleep. Initially, SWS consisted of both Stage 3, which has 20–50 percent delta wave, delta wave activity, and Stage 4, which has more tha ...
one
hemisphere Hemisphere may refer to: * A half of a sphere A sphere (from Greek language, Greek —, "globe, ball") is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a circle in two-dimensional space. A sphere is ...
of the brain at a time. The birds tend to exercise this ability depending upon its position relative to the outside of the flock. This may allow the eye opposite the sleeping hemisphere to remain vigilant for
predator Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical en ...

predator
s by viewing the outer margins of the flock. This adaptation is also known from
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as Pinniped, seals, Cetacea, whales, Sirenia, manatees, sea otters and polar bears. They are an informal group, ...
s.
Communal roosting Communal roosting is an animal behavior where a group of individuals, typically of the same species, congregate in an area for a few hours based on an external signal and will return to the same site with the reappearance of the signal. Environment ...
is common because it lowers the loss of body heat and decreases the risks associated with predators. Roosting sites are often chosen with regard to thermoregulation and safety. Many sleeping birds bend their heads over their backs and tuck their in their back feathers, although others place their beaks among their breast feathers. Many birds rest on one leg, while some may pull up their legs into their feathers, especially in cold weather. Perching birds have a tendon-locking mechanism that helps them hold on to the perch when they are asleep. Many ground birds, such as quails and pheasants, roost in trees. A few parrots of the genus '' Loriculus'' roost hanging upside down. Some
hummingbird Hummingbirds are Bird, birds native to the Americas and comprise the Family (biology), biological family Trochilidae. With about 360 species, they occur from Alaska to Tierra del Fuego, but the vast majority of the species are found in the tropi ...

hummingbird
s go into a nightly state of
torpor Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature Thermoregulation is the ability of an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμό ...
accompanied with a reduction of their metabolic rates. This shows in nearly a hundred other species, including
owlet-nightjar Owlet-nightjars are small crepuscular An adult firefly (''Photuris lucicrescens'') or "lightning bug" – a crepuscular beetle A crepuscular animal is one that is active primarily during the twilight period. This is distinguished from d ...
s,
nightjar Nightjars are medium-sized nocturnal or crepuscular birds in the family (biology), family Caprimulgidae and Order (biology), order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called goatsu ...
s, and
woodswallow Woodswallows are soft-plumaged, somber-coloured passerine birds in the genus ''Artamus''. The woodswallows are either treated as a subfamily, Artaminae, in an expanded family Artamidae (also including the subfamily Cracticinae), or as the only gen ...
s. One species, the
common poorwill The common poorwill (''Phalaenoptilus nuttallii'') is a nocturnal bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying o ...
, even enters a state of
hibernation Hibernation is a state of minimal activity and metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological ...

hibernation
. Birds do not have sweat glands, but they may cool themselves by moving to shade, standing in water, panting, increasing their surface area, fluttering their throat or by using special behaviours like urohidrosis to cool themselves.


Breeding


Social systems

Ninety-five per cent of bird species are socially monogamous. These species pair for at least the length of the breeding season or—in some cases—for several years or until the death of one mate. Monogamy allows for both paternal care and biparental care, which is especially important for species in which females require males' assistance for successful brood-rearing. Among many socially monogamous species,
extra-pair copulation Extra-pair copulation (EPC) is a promiscuous mating behaviour in monogamous species. Monogamy is the practice of having only one sexual partner at any one time, forming a long-term bond and combining efforts to raise offspring together; mating ou ...
(infidelity) is common. Such behaviour typically occurs between dominant males and females paired with subordinate males, but may also be the result of forced copulation in ducks and other anatids. For females, possible benefits of extra-pair copulation include getting better genes for her offspring and insuring against the possibility of infertility in her mate. Males of species that engage in extra-pair copulations will closely guard their mates to ensure the parentage of the offspring that they raise. Other mating systems, including
polygyny Polygyny (; from Neoclassical Greek πολυγυνία from πολύ- ''poly-'' "many", and γυνή ''gyne'' "woman" or "wife") is the most common and accepted form of polygamy Polygamy (from Late Greek Late Greek means writings in ...
,
polyandry Polyandry (; from grc-gre, πολυ- ''poly-'', "many" and ἀνήρ ''anēr'', "man") is a form of polygamy Polygamy (from Late Greek Late Greek means writings in the Greek language Greek (modern , romanized: ''Elliniká'', Ancient ...
,
polygamy Polygamy (from Greek language, Late Greek , ''polygamía'', "state of marriage to many spouses") is the practice of marriage, marrying multiple spouses. When a man is married to more than one wife at the same time, sociologists call this poly ...
,
polygynandry Polygynandry is a mating system A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to animals Animals (also called Metazoa) are multicellula ...
, and
promiscuity Promiscuity is the practice of engaging in sexual activity frequently with different Sexual partner, partners or being indiscriminate in the choice of sexual partners. The term can carry a moral judgment if the social ideal for sexual activity is ...
, also occur. Polygamous breeding systems arise when females are able to raise broods without the help of males. Some species may use more than one system depending on the circumstances. Breeding usually involves some form of courtship display, typically performed by the male. Most displays are rather simple and involve some type of
song A song is a musical composition Musical composition can refer to an piece or work of , either or , the of a musical piece or to the process of creating or writing a new piece of music. People who create new compositions are called s ...
. Some displays, however, are quite elaborate. Depending on the species, these may include wing or tail drumming, dancing, aerial flights, or communal lekking. Females are generally the ones that drive partner selection, although in the polyandrous phalaropes, this is reversed: plainer males choose brightly coloured females.
Courtship feeding A nuptial gift is a nutritional gift given by one partner in some animals' sexual reproduction Sexual reproduction is a type of reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organi ...
, billing and are commonly performed between partners, generally after the birds have paired and mated. in males or females in numerous species of birds, including copulation, pair-bonding, and joint parenting of chicks. Over 130 avian species around the world engage in sexual interactions between the same sex or homosexual behaviours. "Same-sex courtship activities may involve elaborate displays, synchronized dances, gift-giving ceremonies, or behaviors at specific display areas including bowers, arenas, or leks."


Territories, nesting and incubation

Many birds actively defend a territory from others of the same species during the breeding season; maintenance of territories protects the food source for their chicks. Species that are unable to defend feeding territories, such as
seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

seabird
s and
swift The Society for Worldwide Interbank Financial Telecommunication (SWIFT), legally S.W.I.F.T. SCRL, is a Belgium, Belgian cooperative society that serves as an intermediary and executor of financial transactions between banks worldwide. It also ...
s, often breed in
colonies In political science, a colony is a territory subject to a form of foreign rule. Though dominated by the foreign colonizers, colonies remain separate from the administration of the original country of the colonizers, the metropole, metropolitan ...
instead; this is thought to offer protection from predators. Colonial breeders defend small nesting sites, and competition between and within species for nesting sites can be intense. All birds lay
amniotic egg Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
s with hard shells made mostly of
calcium carbonate Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

calcium carbonate
. Hole and burrow nesting species tend to lay white or pale eggs, while open nesters lay
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard The leopard (''Pan ...

camouflage
d eggs. There are many exceptions to this pattern, however; the ground-nesting
nightjar Nightjars are medium-sized nocturnal or crepuscular birds in the family (biology), family Caprimulgidae and Order (biology), order Caprimulgiformes, characterised by long wings, short legs, and very short bills. They are sometimes called goatsu ...
s have pale eggs, and camouflage is instead provided by their plumage. Species that are victims of
brood parasites Brood parasites are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular intera ...
have varying egg colours to improve the chances of spotting a parasite's egg, which forces female parasites to match their eggs to those of their hosts. Bird eggs are usually laid in a
nest A nest is a structure built for certain animals to hold eggs Eggs are laid by female animals of many different species, including bird egg, birds, reptiles, amphibians, a few monotreme, mammals, and fish, and many of these have been eaten ...

nest
. Most species create somewhat elaborate nests, which can be cups, domes, plates, beds scrapes, mounds, or burrows.Hansell M (2000). ''Bird Nests and Construction Behaviour''. University of Cambridge Press Some bird nests, however, are extremely primitive;
albatross Albatrosses are very large Seabird, seabirds in the family (biology), family Diomedeidae. They range widely in the Southern Ocean and the North Pacific Ocean, Pacific. They are absent from the North Atlantic Ocean, Atlantic, although fossil rem ...

albatross
nests are no more than a scrape on the ground. Most birds build nests in sheltered, hidden areas to avoid predation, but large or colonial birds—which are more capable of defence—may build more open nests. During nest construction, some species seek out plant matter from plants with parasite-reducing toxins to improve chick survival, and feathers are often used for nest insulation. Some bird species have no nests; the cliff-nesting
common guillemot The common murre or common guillemot (''Uria aalge'') is a large auk. It is also known as the thin-billed murre in North America. It has a Subarctic, circumpolar distribution, occurring in low-Arctic and boreal waters in the North Atlantic and Nor ...
lays its eggs on bare rock, and male
emperor penguin The emperor penguin (''Aptenodytes forsteri'') is the tallest and heaviest of all living penguin species and is Endemism in birds, endemic to Antarctica. The male and female are similar in plumage and size, reaching in length and weighing fr ...

emperor penguin
s keep eggs between their body and feet. The absence of nests is especially prevalent in ground-nesting species where the newly hatched young are
precocial California quail chick (''Callipepla californica''), a precocial chick In biology, precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called ...
. , which optimises temperature for chick development, usually begins after the last egg has been laid. In monogamous species incubation duties are often shared, whereas in polygamous species one parent is wholly responsible for incubation. Warmth from parents passes to the eggs through
brood patch A brood patch is a patch of featherless skin on the underside of birds during the nesting season. Feathers act as inherent insulators, and prevent efficient incubation. Birds have solved this evolutionary dilemma by developing dedicated brood patch ...
es, areas of bare skin on the abdomen or breast of the incubating birds. Incubation can be an energetically demanding process; adult albatrosses, for instance, lose as much as of body weight per day of incubation. The warmth for the incubation of the eggs of
megapode The megapodes, also known as incubator birds or mound-builders, are stocky, medium-large, chicken-like bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four- ...
s comes from the sun, decaying vegetation or volcanic sources. Incubation periods range from 10 days (in
woodpecker Woodpeckers are part of the Family (biology), family Picidae, which also includes the piculets, wrynecks, and sapsuckers. Members of this family are found worldwide, except for Australia, New Guinea, New Zealand, Madagascar, and the extreme pol ...

woodpecker
s,
cuckoo Cuckoos are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...

cuckoo
s and
passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), bi ...
birds) to over 80 days (in albatrosses and
kiwi KIWI (102.9 FM, "Radio Lobo") is a commercial radio station , Sweden , Norway Radio broadcasting is transmission of audio signal, audio (sound), sometimes with related metadata, by radio waves intended to reach a wide audience. In terrestria ...
s). The diversity of characteristics of birds is great, sometimes even in closely related species. Several avian characteristics are compared in the table below.


Parental care and fledging

At the time of their hatching, chicks range in development from helpless to independent, depending on their species. Helpless chicks are termed ''
altricial In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents develop in spurts after birth. The word is derived from the Latin Latin (, or , ) is a classical languag ...
'', and tend to be born small,
blind Blind may refer to: * The state of Visual impairment, blindness, being unable to see * A window blind, a covering for a window Blind may also refer to: Arts, entertainment, and media Films * Blind (2007 film), ''Blind'' (2007 film), a 2007 Dut ...
, immobile and naked; chicks that are mobile and feathered upon hatching are termed ''
precocial California quail chick (''Callipepla californica''), a precocial chick In biology, precocial species are those in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called ...
''. Altricial chicks need help thermoregulating and must be brooded for longer than precocial chicks. The young of many bird species do not precisely fit into either the precocial or altricial category, having some aspects of each and thus fall somewhere on an "altricial-precocial spectrum". Chicks at neither extreme but favouring one or the other may be termed or . The length and nature of parental care varies widely amongst different orders and species. At one extreme, parental care in
megapode The megapodes, also known as incubator birds or mound-builders, are stocky, medium-large, chicken-like bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four- ...
s ends at hatching; the newly hatched chick digs itself out of the nest mound without parental assistance and can fend for itself immediately. At the other extreme, many seabirds have extended periods of parental care, the longest being that of the
great frigatebird The great frigatebird (''Fregata minor'') is a large seabird in the frigatebird family (biology), family. There are major nesting populations in the tropical Pacific (including the Galapagos Islands) and Indian Oceans, as well as a tiny populatio ...
, whose chicks take up to six months to
fledge Fledging is the stage in a flying animal A number of animals are capable of aerial locomotion, either by powered flight or by gliding (flight), gliding. This trait has appeared by evolution many times, without any single common ancestor. Fl ...
and are fed by the parents for up to an additional 14 months. The ''chick guard stage'' describes the period of breeding during which one of the adult birds is permanently present at the nest after chicks have hatched. The main purpose of the guard stage is to aid offspring to thermoregulate and protect them from predation. In some species, both parents care for nestlings and fledglings; in others, such care is the responsibility of only one sex. In some species,
other members Other most often refers to: * Other (philosophy), a concept in psychology and philosophy Other or The Other may also refer to: Books * The Other (Tryon novel), ''The Other'' (Tryon novel), a 1971 horror novel by Tom Tryon * The Other (short story ...
of the same species—usually close relatives of the
breeding pair Breeding pair is a pair of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellul ...
, such as offspring from previous broods—will help with the raising of the young. Such alloparenting is particularly common among the
Corvida The "Corvida" were one of two "parvorders" contained within the suborder Passeri, as proposed in the Sibley-Ahlquist taxonomy, the other being Passerida. Standard taxonomy (biology), taxonomic practice would place them at the rank of infraorder. ...
, which includes such birds as the true
crows A crow is a bird of the genus ''Corvus ''Corvus'' is a widely distributed genus of medium-sized to large birds in the family Corvidae. The genus includes species commonly known as crows, ravens and rook (bird), rooks; there is no consistent d ...

crows
,
Australian magpie The Australian magpie (''Gymnorhina tibicen'') is a medium-sized black and white passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals ( ...

Australian magpie
and fairy-wrens, but has been observed in species as different as the
rifleman A rifleman is an infantry soldier armed with a rifling, rifled long gun. Although the rifleman role had its origin with 16th century hand cannoneers and 17th century musketeers, the term originated in the 18th century with the introduction o ...
and
red kite The red kite (''Milvus milvus'') is a medium-large bird of prey Birds of prey, also known as raptors, include species of bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of egg ...

red kite
. Among most groups of animals, male parental care is rare. In birds, however, it is quite common—more so than in any other vertebrate class. Although territory and nest site defence, incubation, and chick feeding are often shared tasks, there is sometimes a
division of labour The division of labour is the separation of tasks in any economic system An economic system, or economic order, is a system A system is a group of interacting Interaction is a kind of action that occurs as two or more objects have an ...
in which one mate undertakes all or most of a particular duty. The point at which chicks
fledge Fledging is the stage in a flying animal A number of animals are capable of aerial locomotion, either by powered flight or by gliding (flight), gliding. This trait has appeared by evolution many times, without any single common ancestor. Fl ...
varies dramatically. The chicks of the '' Synthliboramphus'' murrelets, like the
ancient murrelet The ancient murrelet (') is a bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a hi ...
, leave the nest the night after they hatch, following their parents out to sea, where they are raised away from terrestrial predators. Some other species, such as ducks, move their chicks away from the nest at an early age. In most species, chicks leave the nest just before, or soon after, they are able to fly. The amount of parental care after fledging varies; albatross chicks leave the nest on their own and receive no further help, while other species continue some supplementary feeding after fledging. Chicks may also follow their parents during their first
migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
.


Brood parasites

Brood parasitism Brood parasites are organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interact ...
, in which an egg-layer leaves her eggs with another individual's brood, is more common among birds than any other type of organism.Davies N (2000). ''Cuckoos, Cowbirds and other Cheats''. T. & A. D. Poyser: London After a parasitic bird lays her eggs in another bird's nest, they are often accepted and raised by the host at the expense of the host's own brood. Brood parasites may be either ''obligate brood parasites'', which must lay their eggs in the nests of other species because they are incapable of raising their own young, or ''non-obligate brood parasites'', which sometimes lay eggs in the nests of
conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical Biochemistry or biological chemistry, is the study of chemical process In a scientific Science (from the Latin Latin (, or , ) is a class ...
s to increase their reproductive output even though they could have raised their own young. One hundred bird species, including
honeyguide Honeyguides (family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subj ...
s,
icterid Icterids () or New World blackbirds make up a family, the Icteridae (), of small to medium-sized, often colorful, New World passerine birds. Most species have black as a predominant plumage color, often enlivened by yellow, orange, or red. The s ...
s, and
ducks Duck is the common name for numerous species of waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and Anati ...
, are obligate parasites, though the most famous are the
cuckoo Cuckoos are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...

cuckoo
s. Some brood parasites are adapted to hatch before their host's young, which allows them to destroy the host's eggs by pushing them out of the nest or to kill the host's chicks; this ensures that all food brought to the nest will be fed to the parasitic chicks.


Sexual selection

Birds have
evolved Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

evolved
a variety of
mating In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...

mating
behaviours, with the
peacock Peafowl is a common name for three bird species in the genera Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of naming, def ...

peacock
tail being perhaps the most famous example of
sexual selection Sexual selection is a mode of natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrat ...
and the
Fisherian runaway Fisherian runaway or runaway selection is a sexual selection Sexual selection is a mode of natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right ...
. Commonly occurring
sexual dimorphism Sexual dimorphism is the condition where the sex Sex is either of two divisions, typically male Male (♂) is the sex of an organism that produces the gamete known as sperm. A male gamete can fuse with a larger female gamete, or ovum, in ...
s such as size and colour differences are energetically costly attributes that signal competitive breeding situations. Many types of avian
sexual selection Sexual selection is a mode of natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype right , Here the relation between genotype and phenotype is illustrat ...
have been identified; intersexual selection, also known as female choice; and intrasexual competition, where individuals of the more abundant sex compete with each other for the privilege to mate. Sexually selected traits often evolve to become more pronounced in competitive breeding situations until the trait begins to limit the individual's fitness. Conflicts between an individual fitness and signalling adaptations ensure that sexually selected ornaments such as plumage colouration and courtship behaviour are "honest" traits. Signals must be costly to ensure that only good-quality individuals can present these exaggerated sexual ornaments and behaviours.


Inbreeding depression

Inbreeding causes early death (
inbreeding depression Inbreeding depression is the reduced biological fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of natural and sexual selection File:Sexual Selection with Peafowl.gif, 250px, Sexual se ...
) in the
zebra finch The zebra finch (''Taeniopygia guttata'') is the most common estrildid finch of Central Australia Central Australia, also known as the Alice Springs Region ( aer, Mparntwe Ampere), is one of the five regions in the Northern Territory of ...

zebra finch
''Taeniopygia guttata''. Embryo survival (that is, hatching success of fertile eggs) was significantly lower for mating pairs than for unrelated pairs. ''Geospiza scandens'' experiences
inbreeding depression Inbreeding depression is the reduced biological fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of natural and sexual selection File:Sexual Selection with Peafowl.gif, 250px, Sexual se ...
(reduced survival of offspring) and the magnitude of this effect is influenced by environmental conditions such as low food availability.


Inbreeding avoidance

Incestuous matings by the purple-crowned fairy wren ''Malurus coronatus'' result in severe fitness costs due to
inbreeding depression Inbreeding depression is the reduced biological fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of natural and sexual selection File:Sexual Selection with Peafowl.gif, 250px, Sexual se ...
(greater than 30% reduction in hatchability of eggs). Females paired with related males may undertake extra pair matings (see Promiscuity#Other animals for 90% frequency in avian species) that can reduce the negative effects of inbreeding. However, there are ecological and demographic constraints on extra pair matings. Nevertheless, 43% of broods produced by incestuously paired females contained extra pair young. Inbreeding depression occurs in the
great tit The great tit (''Parus major'') is a passerine A passerine () is any bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular euk ...

great tit
(''Parus major'') when the offspring produced as a result of a mating between close relatives show reduced fitness. In natural populations of ''Parus major'', inbreeding is avoided by dispersal of individuals from their birthplace, which reduces the chance of mating with a close relative. Southern pied babblers ''Turdoides bicolor'' appear to avoid inbreeding in two ways. The first is through dispersal, and the second is by avoiding familiar group members as mates. Although both males and females disperse locally, they move outside the range where genetically related individuals are likely to be encountered. Within their group, individuals only acquire breeding positions when the opposite-sex breeder is unrelated.
Cooperative breeding Cooperative breeding is a social system In , social system is the patterned network of relationships constituting a coherent whole that exist between individuals, groups, and institutions. It is the formal of role and status that can form in a ...
in birds typically occurs when offspring, usually males, delay dispersal from their natal group in order to remain with the family to help rear younger kin. Female offspring rarely stay at home, dispersing over distances that allow them to breed independently, or to join unrelated groups. In general, inbreeding is avoided because it leads to a reduction in progeny fitness (
inbreeding depression Inbreeding depression is the reduced biological fitness Fitness (often denoted w or ω in population genetics models) is the quantitative representation of natural and sexual selection File:Sexual Selection with Peafowl.gif, 250px, Sexual se ...
) due largely to the homozygous expression of deleterious recessive alleles.
Cross-fertilisation Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing unrelated genetic material into a breeding line. It increases genetic diversity Genetic diversity is the total number of gen ...
between unrelated individuals ordinarily leads to the masking of deleterious recessive alleles in progeny.


Ecology

Birds occupy a wide range of ecological positions. While some birds are generalists, others are highly specialised in their habitat or food requirements. Even within a single habitat, such as a forest, the occupied by different species of birds vary, with some species feeding in the
forest canopy A forest is an area of land dominated by tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and leaves in most species. In some usages, the definition of a t ...

forest canopy
, others beneath the canopy, and still others on the forest floor. Forest birds may be
insectivore A robber fly eating a _.html" ;"title="hoverfly ">hoverfly An insectivore is a Carnivore">carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since pre ...
s,
frugivore A frugivore is an animal that thrives mostly on raw fruits or succulent fruit-like produce of plants such as roots, shoots, nuts and seeds. Approximately 20% of mammalian herbivores eat fruit. Frugivores are highly dependent on the abundance and ...
s, and
nectarivore In zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Bio ...
s. Aquatic birds generally feed by fishing, plant eating, and piracy or
kleptoparasitism Kleptoparasitism (etymologically, parasitism Parasitism is a close relationship between species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Bioche ...
. Birds of prey specialise in hunting mammals or other birds, while vultures are specialised
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation Predation is a biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study ...
s.
Avivore file:American Kestrel and American Pipit (2256510207).jpg, American kestrel eating bird. An avivore is a specialized predator of birds, with birds making up a large proportion of its diet. Such bird-eating animals come from a range of groups. Birds ...
s are animals that are specialised at preying on birds. Some nectar-feeding birds are important pollinators, and many frugivores play a key role in seed dispersal. Plants and pollinating birds often
coevolve In biology, coevolution occurs when two or more species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined ...
, and in some cases a flower's primary pollinator is the only species capable of reaching its nectar. Birds are often important to island ecology. Birds have frequently reached islands that mammals have not; on those islands, birds may fulfil ecological roles typically played by larger animals. For example, in New Zealand nine species of
moa Moa (order Order, ORDER or Orders may refer to: * Orderliness Orderliness is a quality that is characterized by a person’s interest in keeping their surroundings and themselves well organized, and is associated with other qualities such ...

moa
were important browsers, as are the
kererū The kererū (''Hemiphaga novaeseelandiae'') or New Zealand pigeon is the only pigeon endemic (ecology), endemic to the New Zealand mainland. A large conspicuous pigeon with distinctive noisy wingbeats, it is the only remaining New Zealand bird ...
and today. Today the plants of New Zealand retain the defensive adaptations evolved to protect them from the extinct moa. Nesting
seabird Seabirds (also known as marine birds) are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the ...

seabird
s may also affect the ecology of islands and surrounding seas, principally through the concentration of large quantities of
guano Guano (Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambiguatio ...

guano
, which may enrich the local soil and the surrounding seas. A wide variety of
avian ecology field methods There are many field methods available for conducting bird, avian ecology, ecological research. They can be divided into three types: counts, bird nest, nest monitoring, and capturing and marking. Basic counts Basic bird counts are a good way to e ...
, including counts, nest monitoring, and capturing and marking, are used for researching avian ecology.


Relationship with humans

Since birds are highly visible and common animals, humans have had a relationship with them since the dawn of man. Sometimes, these relationships are mutualistic, like the cooperative honey-gathering among
honeyguide Honeyguides (family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typically subj ...
s and African peoples such as the Borana. Other times, they may be
commensal Commensalism is a long-term biological interaction In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their ph ...

commensal
, as when species such as the
house sparrow The house sparrow (''Passer domesticus'') is a bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form ...

house sparrow
have benefited from human activities. Several bird species have become commercially significant agricultural pests, and some pose an aviation hazard. Human activities can also be detrimental, and have threatened numerous bird species with extinction (
hunting Hunting is the practice of seeking, pursuing and capturing or killing wildlife Wildlife traditionally refers to undomesticated animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism ...

hunting
, avian lead poisoning,
pesticide Pesticides are substances that are meant to control pests Pest or The Pest may refer to: Science and medicine * Pest (organism), an animal or plant detrimental to humans or human concerns ** Weed, a plant considered undesirable * Infectious d ...
s,
roadkill Roadkill is an animal or animals that have been struck and killed by drivers of motor vehicle A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled vehicle A vehicle (from la, vehiculum) is a machi ...

roadkill
,
wind turbine A wind turbine is a device that converts Religious conversion is the adoption of a set of beliefs identified with one particular religious denomination A religious denomination is a subgroup within a religion Religion is a social ...

wind turbine
kills and predation by pet
cat The cat (''Felis catus'') is a domestic Domestic may refer to: In the home * Anything relating to the human home A home, or domicile, is a space used as a permanent or semi-permanent residence for an individual, group or famil ...

cat
s and
dog The dog or domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the ...

dog
s are common causes of death for birds). Birds can act as vectors for spreading diseases such as
psittacosis Psittacosis—also known as parrot fever, and ornithosis—is a zoonotic A zoonosis (plural zoonoses, or zoonotic diseases) is an infectious disease caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) th ...
,
salmonellosis Salmonellosis is a symptomatic infection caused by bacteria Bacteria (; common noun bacteria, singular bacterium) are a type of Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganism ...
,
campylobacteriosis Campylobacteriosis is an infection An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the infectious agent ...

campylobacteriosis
, mycobacteriosis (avian
tuberculosis Tuberculosis (TB) is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, disease-causing agents, their multiplication, and the reaction of host (biology), host tissues to the in ...

tuberculosis
),
avian influenza Avian influenza, known informally as avian flu or bird flu, is a variety of influenza caused by viruses adapted to birds.
(bird flu),
giardiasis Giardiasis is a parasitic disease caused by ''Giardia duodenalis'' (also known as ''G. lamblia'' and ''G. intestinalis''). About 10% of those infected have no symptoms. Individuals who experience symptoms may have diarrhea, abdominal pain ...
, and
cryptosporidiosis Cryptosporidiosis, sometimes informally called crypto, is a parasitic disease A parasitic disease, also known as parasitosis, is an infectious disease An infection is the invasion of an organism's body Tissue (biology), tissues by Pathogen, ...
over long distances. Some of these are
zoonotic diseases A zoonosis (plural zoonoses, or zoonotic diseases) is an infectious disease caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has Cross-species transmission, jumped from an animal (usually a vertebrat ...
that can also be transmitted to humans.


Economic importance

Domesticated birds raised for meat and eggs, called
poultry Poultry () are domesticated Domestication is a sustained multi-generational relationship in which one group of organisms assumes a significant degree of influence over the reproduction and care of another group to secure a more predictable ...

poultry
, are the largest source of animal protein eaten by humans; in 2003, tons of poultry and tons of eggs were produced worldwide.
Chicken The chicken (''Gallus gallus domesticus'') is a domestication, domesticated subspecies of the red junglefowl originally from Southeastern Asia. Rooster or cock is a term for an adult male bird, and a younger male may be called a cockerel. A m ...

Chicken
s account for much of human poultry consumption, though domesticated
turkeys The turkey is a large bird in the genus ''Meleagris'', native to North America. There are two extant turkey species: the wild turkey (''Meleagris gallopavo'') of eastern and central North America and the ocellated turkey (''Meleagris ocellata ...

turkeys
,
ducks Duck is the common name for numerous species of waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and Anati ...

ducks
, and
geese A goose (plural geese) is a bird of any of several waterfowl Anseriformes is an order (biology), order of birds that comprise about 180 living species in three families: Anhimidae (the 3 screamers), Anseranatidae (the magpie goose), and An ...

geese
are also relatively common. Many species of birds are also hunted for meat. Bird hunting is primarily a recreational activity except in extremely undeveloped areas. The most important birds hunted in North and South America are waterfowl; other widely hunted birds include
pheasant Pheasants () are birds of several genera within the family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same sp ...

pheasant
s,
wild turkey The wild turkey (''Meleagris gallopavo'') is an upland ground bird native to North America North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as ...

wild turkey
s, quail,
dove Columbidae () is a bird family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, ...

dove
s,
partridge The species of partridge is any member of a paraphyletic group of organisms that consist of all medium-sized non-migratory birds, with a wide native distribution throughout Europe, Asia, and parts of Africa. They are sometimes grouped in the P ...

partridge
,
grouse Grouse are a group of birds from the order (biology), order Galliformes, in the family (biology), family Phasianidae. Grouse are presently assigned to the Tribe (biology), tribe Tetraonini (formerly the subfamily Tetraoninae and the family Tetr ...

grouse
,
snipe A snipe is any of about 26 wading bird FIle:Vadare - Ystad-2021.jpg, 245px, A flock of Dunlins and Red knots Waders are birds of the order Charadriiformes commonly found along shorelines and mudflats that wikt:wade#Etymology 1, wade in order ...

snipe
, and
woodcock The woodcocks are a group of seven or eight very similar living species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species ...

woodcock
.
Muttonbirding Muttonbirding is the seasonal harvesting of the chicks of petrel Petrels are tube-nosed seabirds in the bird order Procellariiformes. Description The common name does not indicate relationship beyond that point, as "petrels" occur in three of ...
is also popular in Australia and New Zealand. Although some hunting, such as that of muttonbirds, may be sustainable, hunting has led to the extinction or endangerment of dozens of species. Other commercially valuable products from birds include feathers (especially the
down Down most often refers to: * Down, the relative direction Body relative directions (also known as egocentric coordinates) are orientation (geometry), geometrical orientations relative to a body such as a human person's. The most common one ...
of geese and ducks), which are used as insulation in clothing and bedding, and seabird faeces (
guano Guano (Spanish Spanish may refer to: * Items from or related to Spain: **Spaniards, a nation and ethnic group indigenous to Spain **Spanish language **Spanish cuisine Other places * Spanish, Ontario, Canada * Spanish River (disambiguatio ...

guano
), which is a valuable source of phosphorus and nitrogen. The
War of the Pacific The War of the Pacific ( es, link=no, Guerra del Pacífico), also known as the Saltpeter War ( es, link=no, Guerra del salitre) and by War of the Pacific#Etymology, multiple other names, was a war between Chile and a Treaty of Defensive Allianc ...
, sometimes called the Guano War, was fought in part over the control of guano deposits. Birds have been domesticated by humans both as pets and for practical purposes. Colourful birds, such as
parrots Parrots, also known as psittacines , are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the K ...
and
myna The myna (; also spelled mynah) is a bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kin ...
s, are bred in
captivity Captivity, or being held captive, is a state wherein humans or other animals are confined to a particular space and prevented from leaving or moving freely. An example in humans is imprisonment. Prisoners of war are usually held in captivity by a g ...

captivity
or kept as pets, a practice that has led to the illegal trafficking of some
endangered species An endangered species is a species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group ...
.
Falcon Falcons () are birds of prey Birds of prey, also known as raptors, include species of bird that primarily hunt and feed on vertebrates that are large relative to the hunter. Additionally, they have Bird vision, keen eyesight for detecting fo ...

Falcon
s and
cormorant Phalacrocoracidae is a family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, typ ...

cormorant
s have long been used for
hunting Hunting is the practice of seeking, pursuing and capturing or killing wildlife Wildlife traditionally refers to undomesticated animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism ...

hunting
and
fishing Fishing is the activity of trying to catch fish Fish are , , -bearing animals that lack with . Included in this definition are the living , s, and and as well as various extinct related groups. Around 99% of living fish species are ...

fishing
, respectively.
Messenger pigeon The true messenger pigeon is a variety of domestic pigeons (''Columba livia domestica'') derived from the wild rock dove, selective breeding, selectively bred for its ability to find its way home over extremely long distances. The rock dove has a ...

Messenger pigeon
s, used since at least 1 AD, remained important as recently as
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a global war A world war is "a war War is an intense armed conflict between states State may refer to: Arts, entertainment, and media Literatur ...
. Today, such activities are more common either as hobbies, for entertainment and tourism, or for sports such as
pigeon racing Pigeon racing is the sport of releasing specially trained homing pigeon The true messenger pigeon is a variety of domestic pigeons (''Columba livia domestica'') derived from the wild rock dove, selective breeding, selectively bred for its abi ...
. Amateur bird enthusiasts (called birdwatchers, twitchers or, more commonly,
birders Birdwatching, or birding, is a form of wildlife observation in which the observation of birds is a recreational activity or citizen science. It can be done with the naked eye, through a visual enhancement device like binoculars and telescopes, ...
) number in the millions. Many homeowners erect
bird feeder A birdfeeder, bird feeder, bird table, or tray feeder are devices placed outdoors to supply bird food Bird food or bird seed is food (often varieties of seed A seed is an embryonic plant enclosed in a protective outer covering. The for ...

bird feeder
s near their homes to attract various species.
Bird feeding Bird feeding is the activity of feeding wild birds, often by means of a bird feeder. With a recorded history dating to the 6th century, the feeding of wild birds has been encouraged and celebrated in the United States and United Kingdom, with it be ...

Bird feeding
has grown into a multimillion-dollar industry; for example, an estimated 75% of households in Britain provide food for birds at some point during the winter.


In religion and mythology

Birds play prominent and diverse roles in religion and mythology. In religion, birds may serve as either messengers or priests and leaders for a
deity A deity or god is a supernatural being considered divinity, divine or sacred. The ''Oxford Dictionary of English'' defines deity as a God (male deity), god or goddess (in a polytheistic religion), or anything revered as divine. C. Scott Littleto ...

deity
, such as in the Cult of
Makemake Makemake (minor-planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur (minor planet), centaur, trans-Neptunian object and dwarf planet but not comet) ...
, in which the
Tangata manu The ''Tangata manu'' ("bird-man," from "human beings" + "bird") was the winner of a traditional competition on Rapa Nui Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile Chile (, ; ), ...
of
Easter Island Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a continent ...

Easter Island
served as chiefs or as attendants, as in the case of
Hugin and Munin 's shoulders in an illustration from an 18th-century Iceland Iceland ( is, Ísland; ) is a Nordic countries, Nordic island country in the Atlantic Ocean, North Atlantic Ocean, with a population of 356,991 and an area of , making it the most li ...
, the two
common raven The common raven (''Corvus corax''), also known as the western raven or northern raven when discussing the raven at the subspecies level, is a large all-black passerine A passerine () is any bird Birds are a group of warm-bl ...
s who whispered news into the ears of the
Norse god In Germanic paganism Germanic paganism included various religious Religion is a - of designated and practices, , s, s, , , , , or , that relates humanity to , , and elements; however, there is no scholarly consensus over what precise ...
Odin Odin (; from non, Óðinn, ) is a widely revered god in Germanic mythology Germanic mythology consists of the body of myth Myth is a folklore genre consisting of narratives that play a fundamental role in a society, such as foundat ...

Odin
. In several civilisations of
ancient Italy The history of Italy covers the Ancient Period, the Middle Ages and the modern era. Since classical times, ancient Phoenicians, Magna Graecia, Greeks, Etruscan civilization, Etruscans, and Celts have inhabited the Italian Peninsula, with various ...
, particularly
Etruscan__NOTOC__ Etruscan may refer to: Ancient civilisation *The Etruscan language, an extinct language in ancient Italy *Something derived from or related to the Etruscan civilization **Etruscan architecture **Etruscan art **Etruscan cities **Etruscan ...
and
Roman Roman or Romans most often refers to: *Rome , established_title = Founded , established_date = 753 BC , founder = King Romulus , image_map = Map of comune of Rome (metropolitan city of Capital Rome, region Laz ...
religion Religion is a social Social organisms, including humans, live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchange is voluntary/involuntary. Etymology ...
, priests were involved in
augur An augur was a priest and official in the classical Roman world. His main role was the practice of augury Augury is the practice from ancient Roman religion Religion in ancient Rome includes the ancestral ethnic religion In religiou ...

augur
y, or interpreting the words of birds while the "auspex" (from which the word "auspicious" is derived) watched their activities to foretell events. They may also serve as
religious symbols A religious symbol is an iconic representation intended to represent a specific religion Religion is a social Social organisms, including humans, live collectively in interacting populations. This interaction is considered social whether the ...
, as when
Jonah Jonah or Jonas, ''Yōnā'', "dove"; gr, Ἰωνᾶς ''Iōnâs''; ar, يونس ' or '; Latin: ''Ionas'' Ben (Hebrew), son of Amittai, is a prophet in the Hebrew Bible and the Quran, from Gath-hepher of the northern Kingdom of Israel (Samaria ...

Jonah
(,
dove Columbidae () is a bird family In human society A society is a Social group, group of individuals involved in persistent Social relation, social interaction, or a large social group sharing the same spatial or social territory, ...

dove
) embodied the fright, passivity, mourning, and beauty traditionally associated with doves. Birds have themselves been deified, as in the case of the , which is perceived as Mother Earth by the people of southern India. In the ancient world, doves were used as symbols of the Mesopotamian goddess
Inanna Inanna is an ancient Mesopotamian goddess associated with love, beauty, sex, war, justice and political power. She was originally worshiped in Sumer Sumer ()The name is from '; ''kig̃ir'', written and ,approximately "land of the ...
(later known as Ishtar), the
CanaaniteCanaanite may refer to: *Canaan and Canaanite people, Semitic-speaking region and civilization in the Ancient Near East *Canaanite languages *Canaanite religion *Canaanites (movement), an early Israelite non-Zionist movement. {{disambig Language an ...
mother goddess
Asherah Asherah , ''ʾăšērâ''; Ugaritic language, Ugaritic: 𐎀𐎘𐎗𐎚 ''Aṯirat'', name=, group= in ancient Semitic religion, is a mother goddess who appears in a number of ancient sources. She appears in Akkadian literature, Akkadian wri ...
, Dorothy D. Resig
The Enduring Symbolism of Doves, From Ancient Icon to Biblical Mainstay"
, ''BAR Magazine'' . Bib-arch.org (9 February 2013). Retrieved on 5 March 2013.
and the Greek goddess
Aphrodite Aphrodite; , , ) is an ancient Greek goddess associated with love Love encompasses a range of strong and positive emotion Emotions are mental state, psychological states brought on by neurophysiology, neurophysiological changes, ...

Aphrodite
. In
ancient Greece Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of History of Greece, Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, antiquity ( AD 600). This era wa ...
,
Athena Athena or Athene, often given the epithet An epithet (, ) is a byname, or a descriptive term (word or phrase), accompanying or occurring in place of a name and having entered common usage. It has various shades of meaning when applied ...

Athena
, the goddess of wisdom and patron deity of the city of
Athens , image_skyline = File:Athens Montage L.png, center, 275px, alt=Athens montage. Clicking on an image in the picture causes the browser to load the appropriate article. rect 15 15 985 460 Acropolis of Athens rect 15 475 48 ...

Athens
, had a
little owl The little owl (''Athene noctua''), also known as the owl of Athena or owl of Minerva, is a bird that inhabits much of the temperate and warmer parts of Europe, the Palearctic east to Korea, and North Africa. It was introduced into Britain at t ...

little owl
as her symbol. In religious images preserved from the Inca and Tiwanaku empires, birds are depicted in the process of transgressing boundaries between earthly and underground spiritual realms. Indigenous peoples of the central Andes maintain legends of birds passing to and from metaphysical worlds.


In culture and folklore

Birds have featured in culture and art since prehistoric times, when they were represented in early
cave painting Cave paintings are a type of parietal art In archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. Archaeology is often considered a branch of socio-cultural anthrop ...

cave painting
s. Some birds have been perceived as monsters, including the mythological Roc and the
Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Coo ...
's legendary , a giant bird capable of snatching humans. Birds were later used as symbols of power, as in the magnificent
Peacock Throne The Peacock Throne (Hindustani Hindustani may refer to: * something of, from, or related to Hindustan (another name of India) * Hindustani language, an Indo-Aryan language, whose two official norms are Hindi and Urdu * Fiji Hindi, a variety o ...
of the
Mughal Mughal or Moghul may refer to: * The Mughal Empire of South Asia ** Mughal dynasty ** Mughal emperors ** Mughal people, a social group of South Asia ** Mughal Army, the Army of Mughal Empire * Cultural influences of the Mughal Empire ** Mughal arc ...
and
Persian Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, Persian people, the majority ethnic group in Iran, not to be conflated with the Iranian peoples ** Persian language, an Iranian ...

Persian
emperors. With the advent of scientific interest in birds, many paintings of birds were commissioned for books. Among the most famous of these bird artists was
John James Audubon John James Audubon (born Jean-Jacques Rabin; April 26, 1785 – January 27, 1851) was an American ornithologist Ornithology is a branch of zoology that concerns the "methodological study and consequent knowledge of birds with all that ...

John James Audubon
, whose paintings of North American birds were a great commercial success in Europe and who later lent his name to the
National Audubon Society Audubon may refer to: People * John James Audubon John James Audubon (born Jean-Jacques Rabin; April 26, 1785 – January 27, 1851) was an American ornithology, ornithologist, natural history, naturalist, and Painting, painter. His combin ...
. Birds are also important figures in poetry; for example,
Homer Homer (; grc, Ὅμηρος , ''Hómēros'') was an ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally re ...

Homer
incorporated
nightingale The common nightingale, rufous nightingale or simply nightingale (''Luscinia megarhynchos''), is a small passerine A passerine is any bird of the Order (biology), order Passeriformes (, Latin ''passer'' (“sparrow”) + ''formis'' (“-shape ...
s into his ''
Odyssey The ''Odyssey'' (; grc, Ὀδύσσεια, Odýsseia, ) is one of two major ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí ...
'', and
Catullus Gaius Valerius Catullus (; ), often referred to simply as Catullus (), was a Latin poet of the late Roman Republic The Roman Republic ( la, Rēs pūblica Rōmāna ) was a state of the classical Roman civilization, run through public ...

Catullus
used a sparrow as an erotic symbol in his Catullus 2. The relationship between an
albatross Albatrosses are very large Seabird, seabirds in the family (biology), family Diomedeidae. They range widely in the Southern Ocean and the North Pacific Ocean, Pacific. They are absent from the North Atlantic Ocean, Atlantic, although fossil rem ...

albatross
and a sailor is the central theme of
Samuel Taylor Coleridge Samuel Taylor Coleridge (; 21 October 177225 July 1834) was an , , and who, with his friend , was a founder of the in England and a member of the . He also shared volumes and collaborated with , , and . He wrote the poems ' and ', as well ...

Samuel Taylor Coleridge
's ''
The Rime of the Ancient Mariner ''The Rime of the Ancient Mariner'' (originally ''The Rime of the Ancyent Marinere'') is the longest major poem by the English poet Samuel Taylor Coleridge Samuel Taylor Coleridge (; 21 October 177225 July 1834) was an , , and who, ...
'', which led to the use of the term as a metaphor for a 'burden'. Other
English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the World language, leading lan ...

English
metaphors derive from birds;
vulture fund A vulture fund is a hedge fund A hedge fund is a pooled investment fund Image:Financial info.jpg, The values and performance of collective funds are listed in newspapers. An investment fund is a way of investment, investing money alongsid ...
s and vulture investors, for instance, take their name from the scavenging vulture. Perceptions of bird species vary across cultures.
Owl Owls are bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological k ...

Owl
s are associated with bad luck,
witchcraft In many cultures, witchcraft traditionally means the use of magic Magic or Magick may refer to: * Ceremonial magic, encompasses a wide variety of rituals of magic * Chaos magic#REDIRECT Chaos magic {{Redirect category shell, 1= {{R from m ...

witchcraft
, and death in parts of Africa, but are regarded as wise across much of Europe.
Hoopoe Hoopoes () are colourful bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), ...
s were considered sacred in
Ancient Egypt Ancient Egypt was a civilization  A civilization (or civilisation) is a that is characterized by , , a form of government, and systems of communication (such as ). Civilizations are intimately associated with additional char ...

Ancient Egypt
and symbols of virtue in
Persia Iran ( fa, ایران ), also called Persia, and officially the Islamic Republic of Iran, is a country in Western Asia. It is bordered to the northwest by Armenia and Azerbaijan, to the north by the Caspian Sea, to the northeast by Tu ...

Persia
, but were thought of as thieves across much of Europe and harbingers of war in
Scandinavia Scandinavia; Sami Places * Sápmi, a cultural region in Northern Europe * Sami, Burkina Faso, a district of the Banwa Province * Sami District, Gambia * Sami, Cephalonia, a municipality in Greece * Sami (ancient city), in Elis, Greece * Sa ...

Scandinavia
. In
heraldry Heraldry () is a discipline relating to the design, display and study of armorial bearings (known as armory), as well as related disciplines, such as vexillology Vexillology () is the study of the history, symbolism and usage of flag A fla ...
, birds, especially
eagles Eagle is the common name for many large birds of prey Birds of prey, also known as raptors, include species of bird Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high ...
, often appear in
coats of arms A coat of arms is a heraldic visual design on an escutcheon (i.e., shield A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, ...
.


In music

In music, birdsong has influenced composers and musicians in several ways: they can be inspired by birdsong; they can intentionally imitate bird song in a composition, as
Vivaldi Antonio Lucio Vivaldi (, ; ; 4 March 1678 – 28 July 1741) was an ItalianMichael Talbot and the Editors of the Encyclopædia Britannica, Baroque The Baroque (, ; ) is a style Style is a manner of doing or presenting things and may ...

Vivaldi
,
Messiaen Olivier Eugène Prosper Charles Messiaen (, ; ; December 10, 1908 – April 27, 1992) was a French composer, organist, and ornithology, ornithologist, one of the major composers of the 20th century. His music is rhythmically complex; Harmon ...
, and did, along with many later composers; they can incorporate recordings of birds into their works, as
Ottorino Respighi Ottorino Respighi ( , , ; 9 July 187918 April 1936) was an Italian composer, violinist, teacher, and musicologist Musicology (from Greek 'μουσική' (mousikē) for 'music' and 'λογος' (logos) for 'domain of study') is the scholarly ...
first did; or like
Beatrice Harrison Beatrice Harrison (9 December 1892 – 10 March 1965) was a British cellist active in the first half of the 20th century. She gave first performances of several important English works, especially those of Frederick Delius, and made the first or ...

Beatrice Harrison
and David Rothenberg, they can duet with birds.


Conservation

Although human activities have allowed the expansion of a few species, such as the
barn swallow The barn swallow (''Hirundo rustica'') is the most widespread species of swallow The swallows, martins, and saw-wings, or Hirundinidae, are a family of passerine A passerine is any bird of the Order (biology), order Passeriformes (, Lat ...

barn swallow
and
European starling The common starling or European starling (''Sturnus vulgaris''), also known simply as the starling in Great Britain and Ireland, is a medium-sized passerine bird in the starling family, Sturnidae. It is about long and has glossy black plumage ...

European starling
, they have caused population decreases or
extinction Extinction is the termination of a kind of organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biol ...

extinction
in many other species. Over a hundred bird species have gone extinct in historical times, although the most dramatic human-caused avian extinctions, eradicating an estimated 750–1800 species, occurred during the human colonisation of
Melanesia Melanesia (, ) is a subregion A subregion is a part of a larger region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabi ...

Melanesia
n,
Polynesia Polynesia (, ; from grc, πολύς "many" and grc, νῆσος "island") ( to, Faka-Polinisia; mi, Porinihia; haw, Polenekia; fj, Kai-Polinesia; sm, Polenisia; rar, Porinetia; ty, Pōrīnetia; tvl, Polenisia; tkl, Polenihia) is a ...

Polynesia
n, and
Micronesia Micronesia (, ; from grc, μικρός ''mikrós'' "small" and ''nêsos'' "island") is a subregion A subregion is a part of a larger region In geography Geography (from Greek: , ''geographia'', literally "earth description") is ...

Micronesia
n islands. Many bird populations are declining worldwide, with 1,227 species listed as
threatened Threatened Species are any species (including animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume org ...
by
BirdLife International BirdLife International is a global partnership of non-governmental organization A non-governmental organization, or simply an NGO, is an organization that is, generally, formed independent from government. They are typically nonprofit organ ...
and the
IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization An international organization (also known as an international institut ...
in 2009. The most commonly cited human threat to birds is
habitat loss Habitat destruction (also termed habitat loss and habitat reduction) is the process by which a natural habitat In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the rela ...
. Other threats include overhunting, accidental mortality due to collisions with
buildings A building, or edifice, is a structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a se ...
or
vehicles A vehicle (from la, vehiculum) is a machine A machine is any physical system with ordered structural and functional properties. It may represent human-made or naturally occurring device molecular machine that uses Power (physics), power ...
,
long-line fishing 260px, Longline fishing, or longlining, is a commercial fishing technique. It uses a long line, called the main line, with baited hooks attached at intervals by means of branch lines called ''snoods'' (or ''gangions'').
bycatch Bycatch (or by-catch), in the fishing industry The fishing industry includes any industry or activity concerned with taking, culturing, processing, preserving, storing, transporting, marketing or selling fish or fish products. It is defined by ...
, pollution (including
oil spill An oil spill is the release of a liquid petroleum Petroleum, also known as crude oil and oil, is a naturally occurring, yellowish-black liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum ...
s and pesticide use), competition and predation from nonnative
invasive species An invasive species is an introduced organism that becomes overpopulated and negatively alters its new environment. Although their spread can have beneficial aspects, invasive species adversely affect the invaded habitat Ibex in an ...
, and climate change. Governments and
conservation Conservation is the preservation or efficient use of resources, or the conservation of various quantities under physical laws. Conservation may also refer to: Environment and natural resources * Nature conservation, the protection and manageme ...
groups work to protect birds, either by passing laws that preserve and
restoreRestore may refer to: * ReStore - Retail building supply stores run by local Habitat for Humanity Habitat for Humanity International (HFHI), generally referred to as Habitat for Humanity or Habitat, is an international, Non-governmental organizati ...
bird habitat or by establishing captive populations for reintroductions. Such projects have produced some successes; one study estimated that conservation efforts saved 16 species of bird that would otherwise have gone extinct between 1994 and 2004, including the
California condor The California condor (''Gymnogyps californianus'') is a New World vulture The New World vulture or condor family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relati ...

California condor
and
Norfolk parakeet The Norfolk parakeet (''Cyanoramphus cookii''), also called Tasman parakeet, Norfolk Island green parrot or Norfolk Island red-crowned parakeet, is a species of parrot in the family Psittaculidae. It is endemic to Norfolk Island (located between A ...
.


See also

*
Animal track __notoc__ An animal track is an imprint left behind in soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical elem ...
* Avian sleep *
Bat Bats are mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meanin ...

Bat
*
Glossary of bird terms The following is a glossary of common English language terms used in the description of bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, ...
*
Ornithology Ornithology is a branch of zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, ...

Ornithology
* Paleocene dinosaurs


Notes


Further reading

* Roger Lederer und Carol Burr: ''Latein für Vogelbeobachter: über 3000 ornithologische Begriffe erklärt und erforscht'', aus dem Englischen übersetzt von Susanne Kuhlmannn-Krieg, Verlag DuMont, Köln 2014, . * del Hoyo, Josep; Elliott, Andrew; Sargatal, Jordi (eds.): ''Handbook of the Birds of the World'' (17-volume encyclopaedia), Lynx Edicions, Barcelona, 1992–2010. (''Vol. 1: Ostrich to Ducks'': , etc.). * ''All the Birds of the World'', Lynx Edicions, 2020. * ''National Geographic Field Guide to Birds of North America'', National Geographic, 7th edition, 2017. * ''National Audubon Society Field Guide to North American Birds: Eastern Region'', National Audubon Society, Knopf. * ''National Audubon Society Field Guide to North American Birds: Western Region'', National Audubon Society, Knopf. * Svensson, Lars: ''Birds of Europe'', Princeton University Press, second edition, 2010. * Svensson, Lars: ''Collins Bird Guide: The Most Complete Guide to the Birds of Britain and Europe'', Collins, 2nd edition, 2010.


External links


Birdlife International
– Dedicated to bird conservation worldwide; has a database with about 250,000 records on endangered bird species.
Theory on the real capabilities of birds "vision"
– New findings in the field.



from the
National Audubon Society Audubon may refer to: People * John James Audubon John James Audubon (born Jean-Jacques Rabin; April 26, 1785 – January 27, 1851) was an American ornithology, ornithologist, natural history, naturalist, and Painting, painter. His combin ...

Cornell Lab of Ornithology
*




Ornithology

Sora
– Searchable online research archive; Archives of the following ornithological journals ''
The Auk ''Ornithology'', formerly ''The Auk'' and ''The Auk: Ornithological Advances'', is a peer-reviewed Peer review is the evaluation of work by one or more people with similar competencies as the producers of the work ( peers). It functions as a ...
'', ''
Condor Condor is the common name for two species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the larges ...
'', ''Journal of Field Ornithology, ''North American Bird Bander'', ''Studies in Avian Biology'', ''Pacific Coast Avifauna'', and the ''
Wilson Bulletin ''The Wilson Journal of Ornithology'' (until 2006 ''The Wilson Bulletin'') is a quarterly scientific journal published by the Wilson Ornithological Society. Both the society and its journal were named after American ornithologist Alexander Wilson ( ...
''.
The Internet Bird Collection
– A free library of videos of the world's birds
The Institute for Bird Populations, California

List of field guides to birds
from the International Field Guides database
RSPB bird identifier
– Interactive identification of all UK birds

— University of California Museum of Paleontology. {{Commons category-inline Dinosaurs Animal classes Santonian first appearances Extant Late Cretaceous first appearances Feathered dinosaurs
Taxa named by Carl Linnaeus Taxonomy (biology), Taxa named by Carl Linnaeus (1707−1778), an 18th-century Swedish taxonomist, botanist, and zoologist. Known as the "father of modern taxonomy" – from his inventing and developing binomial nomenclature; the taxonomy (biology) ...