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Beavers are large,
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semiaquatic animals include: * Verte ...
rodents Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are nat ...
in the genus ''Castor'' native to the temperate Northern Hemisphere. There are two
extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...
species: the
North American beaver The North American beaver (''Castor canadensis'') is one of two Extant taxon, extant beaver species, along with the Eurasian beaver (''Castor fiber''). It is native to North America and introduced in South America (Patagonia) and Europe (primari ...
(''Castor canadensis'') and the
Eurasian beaver The Eurasian beaver (''Castor fiber'') or European beaver is a beaver species that was once widespread in Eurasia, but was hunted to near-extinction for both its fur and castoreum. At the turn of the 20th century, only about 1,200 beavers survi ...
(''C. fiber''). Beavers are the second-largest living rodents after the
capybaras The capybaraAlso called capivara (in Brazil), capiguara (in Bolivia), chigüire, chigüiro, or fercho (in Colombia and Venezuela), carpincho (in Argentina, Paraguay and Uruguay) and ronsoco (in Peru). or greater capybara (''Hydrochoerus hydro ...
. They have stout bodies with large heads, long chisel-like
incisors Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wh ...
, brown or gray
fur Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...
, hand-like front feet, webbed back feet and flat, scaly tails. The two species differ in the shape of the skull and tail and fur color. Beavers can be found in a number of freshwater habitats, such as rivers, streams, lakes and ponds. They are
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
, consuming
tree bark Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines, and shrubs. Bark refers to all the tissues outside the vascular cambium and is a nontechnical term. It overlays the wood and consist ...
,
aquatic plants Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
, grasses and
sedges The Cyperaceae are a family of graminoid (grass-like), monocotyledonous flowering plants known as sedges. The family is large, with some 5,500 known species described in about 90 genera, the largest being the "true sedges" genus ''Carex'' wit ...
. Beavers build
dams A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, ...
and lodges using tree branches, vegetation, rocks and mud; they chew down trees for building material. Dams impound water and lodges serve as shelters. Their infrastructure creates
wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
s used by many other species, and because of their effect on other organisms in the ecosystem, they are considered a
keystone species A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
. Adult males and females live in monogamous pairs with their offspring. When they are old enough, the young will help their parents repair dams and lodges and may also help raise newly born offspring. Beavers hold
territories A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or an ...
and mark them using scent mounds made of mud, debris and
castoreum Castoreum is a yellowish exudate from the castor sacs of mature beavers. Beavers use castoreum in combination with urine to scent mark their territory. Both beaver sexes have a pair of castor sacs and a pair of anal glands, located in two cavities ...
, a liquid substance excreted through the beaver's castor sacs. Beavers can also recognize their kin by their
anal gland Anal may refer to: Related to the anus *Related to the anus of animals: ** Anal fin, in fish anatomy ** Anal vein, in insect anatomy ** Anal scale, in reptile anatomy *Related to the human anus: ** Anal sex, a type of sexual activity involving s ...
secretions and are more likely to tolerate them as neighbors. Historically, beavers have been hunted for their fur, meat and castoreum. Castoreum has been used in medicine, perfume and food flavoring, while beaver pelts have been a major driver of the
fur trade The fur trade is a worldwide industry dealing in the acquisition and sale of animal fur. Since the establishment of a world fur market in the early modern period, furs of boreal, polar and cold temperate mammalian animals have been the mos ...
. Before protections began in the 19th and early 20th centuries,
overhunting Overexploitation, also called overharvesting, refers to harvesting a renewable resource to the point of diminishing returns. Continued overexploitation can lead to the destruction of the resource, as it will be unable to replenish. The term app ...
had nearly exterminated both species. Their populations have rebounded, and they are both listed as
least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
by the
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
of mammals. In human culture, the beaver symbolizes industriousness and is the
national animal This is a list of countries that have officially designated one or more animals as their national animals. National animal {, class="wikitable sortable" ! Country ! Name of animal ! Scientific name (Latin name) ! class="unsortable", Picture ...
of
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
.


Etymology

The English word "beaver" comes from the
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlement of Britain, Anglo ...
word ''beofor'' or ''befor'' and is connected to the
German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ger ...
word ''Biber'' and the
Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () Dutch may also refer to: Places * Dutch, West Virginia, a community in the United States * Pennsylvania Dutch Country People E ...
word ''bever''. The ultimate origin of the word is from an
Indo-European The Indo-European languages are a language family native to the overwhelming majority of Europe, the Iranian plateau, and the northern Indian subcontinent. Some European languages of this family, English, French, Portuguese, Russian, Dutch ...
root for "brown". The
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
name ''Castor'' has its origin in the Greek ''kastor'' and translates as "beaver". The name "beaver" is the source for several names of places in Europe including ''Beverley'', ''Bièvres'', ''Biberbach'', ''Biebrich'', ''Bibra'', ''Bibern'', ''Bibrka'', ''Bobr'', ''Bjurbäcker'', ''Bjurfors'', ''Bober'', ''Bóbrka'' and ''Bjurlund''.


Taxonomy

There are two extant species: the
North American beaver The North American beaver (''Castor canadensis'') is one of two Extant taxon, extant beaver species, along with the Eurasian beaver (''Castor fiber''). It is native to North America and introduced in South America (Patagonia) and Europe (primari ...
(''Castor canadensis'') and the
Eurasian beaver The Eurasian beaver (''Castor fiber'') or European beaver is a beaver species that was once widespread in Eurasia, but was hunted to near-extinction for both its fur and castoreum. At the turn of the 20th century, only about 1,200 beavers survi ...
(''C. fiber''). The Eurasian beaver is slightly longer with a more lengthened skull, triangular
nasal cavities The nasal cavity is a large, air-filled space above and behind the nose in the middle of the face. The nasal septum divides the cavity into two cavities, also known as fossae. Each cavity is the continuation of one of the two nostrils. The nasal c ...
—as opposed to the square ones of the North American species—, lighter fur color and a narrower tail.
Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
coined the genus ''Castor'' in 1758; he also coined the specific (species) epithet ''fiber''. German zoologist
Heinrich Kuhl Heinrich Kuhl (17 September 1797 – 14 September 1821) was a German people, German naturalist and zoologist. Kuhl was born in Hanau (Hesse, Germany). Between 1817 and 1820, he was the assistant of professor Th. van Swinderen, docent natural hi ...
coined ''C. canadensis'' in 1820. However, they were not confirmed to be separate species until the 1970s when
chromosomal A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...
evidence became available. (The Eurasian has 48 chromosomes, versus the North American's 40.) Prior to that, many considered them the same species. The difference in chromosome numbers prevents them from interbreeding. 25 subspecies have been classified for ''C. canadensis'' and nine for ''C. fiber''.


Evolution

Beavers belong to the rodent suborder
Castorimorpha Castorimorpha is the suborder of rodents containing the beavers and the kangaroo rats. A 2017 study using retroposon markers indicated that they are most closely related to the Anomaluromorpha (the scaly-tailed squirrels and the springhare) and ...
, along with
Heteromyidae Heteromyidae is a family of rodents consisting of kangaroo rats, kangaroo mice, pocket mice and spiny pocket mice. Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the gen ...
(
kangaroo rats Kangaroo rats, small mostly nocturnal rodents of genus ''Dipodomys'', are native to arid areas of western North America. The common name derives from their bipedal form. They hop in a manner similar to the much larger kangaroo, but developed thi ...
and
kangaroo mice A kangaroo mouse is either one of the two species of jumping mouse (genus ''Microdipodops'') native to the deserts of the southwestern United States, predominantly found in the state of Nevada. The name "kangaroo mouse" refers to the species' ex ...
), and the gophers. Modern beavers are the only extant members of the family
Castoridae The family Castoridae contains the two living species of beavers and their fossil relatives. A highly diverse group of rodents within this family once roamed the earth, but only a single genus is extant today, '' Castor''. Characteristics C ...
. They originated in North America in the late
Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...
and colonized Eurasia via the
Bering Land Bridge Beringia is defined today as the land and maritime area bounded on the west by the Lena River in Russia; on the east by the Mackenzie River in Canada; on the north by 72 degrees north latitude in the Chukchi Sea; and on the south by the tip of ...
in the early Oligocene, coinciding with the ''
Grande Coupure Grande means "large" or "great" in many of the Romance languages. It may also refer to: Places * Grande, Germany, a municipality in Germany *Grande Communications, a telecommunications firm based in Texas *Grande-Rivière (disambiguation) *Arroi ...
'', a time of significant changes in animal species around 33million years ago (mya). The more basal castorids had several unique features; more complex
occlusion Occlusion may refer to: Health and fitness * Occlusion (dentistry), the manner in which the upper and lower teeth come together when the mouth is closed * Occlusion miliaria, a skin condition * Occlusive dressing, an air- and water-tight trauma ...
between cheek teeth, parallel rows of upper teeth, premolars being only slightly smaller than molars, the presence of a third set of premolars (P3), a
hole A hole is an opening in or through a particular medium, usually a solid body. Holes occur through natural and artificial processes, and may be useful for various purposes, or may represent a problem needing to be addressed in many fields of en ...
in the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the foot ...
of the inner ear, a smooth
palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the throat. Together with the maxillae, they comprise the hard palate. (''Palate'' is derived from the Latin ''pa ...
(with the palatine opening closer to the rear end of the bone), and a longer
snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...
. More
derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...
castorids have less complex occlusion, upper tooth rows that create a V-shape towards the back, larger second premolars compared to molars, absence of a third premolar set and stapes hole, a more grooved palatine (with the opening shifted towards the front), and reduced
incisive foramen In the human mouth, the incisive foramen (also known as: "''anterior palatine foramen''", or "''nasopalatine foramen''") is the opening of the incisive canals on the hard palate immediately behind the incisor teeth. It gives passage to blood ves ...
. Members of the subfamily ''Palaeocastorinae'' appeared in late Oligocene North America. This group consisted primarily of smaller animals with relatively large front legs, a flattened skull and a reduced tail, all features of a
fossorial A fossorial () animal is one adapted to digging which lives primarily, but not solely, underground. Some examples are badgers, naked mole-rats, clams, meerkats, and mole salamanders, as well as many beetles, wasps, and bees. Prehistoric eviden ...
(burrowing) lifestyle. In the early
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
(about 24 mya), castorids
evolved Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation t ...
a
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semiaquatic animals include: * Verte ...
lifestyle. Members of the subfamily
Castoroidinae The family Castoridae contains the two living species of beavers and their fossil relatives. A highly diverse group of rodents within this family once roamed the earth, but only a single genus is extant today, '' Castor''. Characteristics C ...
are considered to be a
sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
to modern beavers, and included giants like ''
Castoroides ''Castoroides'' (Latin: "beaver" (castor), "like" (oides)), or giant beaver, is an extinct genus of enormous, bear-sized beavers that lived in North America during the Pleistocene. Two species are currently recognized, ''C. dilophidus'' in the S ...
'' of North America and ''
Trogontherium ''Trogontherium'' is an extinct genus of giant beavers, ranging from the Late Pliocene to the Late Pleistocene. It is not closely related to the North American giant beavers of the genus ''Castoroides''. Fossils of ''Trogontherium'' have been fou ...
'' of Eurasia. ''Castoroides'' is estimated to have had a length of and a weight of . Fossils of one genus in Castoroidinae, ''
Dipoides ''Dipoides'' is an extinct genus of beaver-grouped rodents. ''Dipoides'' were about two thirds the size of modern Canadian beavers. Where modern beavers have square chisel shaped teeth, ''Dipoides'' teeth were rounded. However an excavation of ...
'', have been found near piles of chewed wood, though it appears to have been an inferior woodcutter compared to ''Castor''. Researchers suggest that modern beavers and Castoroidinae shared a bark-eating
common ancestor Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. All living beings are in fact descendants of a unique ancestor commonly referred to as the last universal comm ...
. Dam and lodge-building likely developed from bark-eating, and allowed beavers to survive in the harsh winters of the
subarctic The subarctic zone is a region in the Northern Hemisphere immediately south of the true Arctic, north of humid continental regions and covering much of Alaska, Canada, Iceland, the north of Scandinavia, Siberia, and the Cairngorms. Generally, ...
. There is no conclusive evidence for this behavior occurring in non-''Castor'' species. The genus ''Castor'' likely originated in Eurasia; The earliest fossil remains appear to be ''C. neglectus'', found in Germany and dated 12–10 mya.
Mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...
studies place the common ancestor of the two living species at around 8 mya. The ancestors of the North American beaver would have crossed the Bering Land Bridge around 7.5 mya. ''Castor'' may have competed with members of Castoroidinae, which led to
niche differentiation In ecology, niche differentiation (also known as niche segregation, niche separation and niche partitioning) refers to the process by which competing species use the environment differently in a way that helps them to coexist. The competitive excl ...
. The fossil species ''C. praefiber'' was likely the ancestor of the Eurasian beaver. '' C. californicus'' from the
Early Pleistocene The Early Pleistocene is an unofficial sub-epoch in the international geologic timescale in chronostratigraphy, being the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently estimated to span the time ...
of North America was similar to but larger than the extant North American beaver.


Characteristics and adaptations

Beavers are the second-largest living rodents, after the
capybara The capybaraAlso called capivara (in Brazil), capiguara (in Bolivia), chigüire, chigüiro, or fercho (in Colombia and Venezuela), carpincho (in Argentina, Paraguay and Uruguay) and ronsoco (in Peru). or greater capybara (''Hydrochoerus hydro ...
s. They have a head-body length of , with a tail, a shoulder height of and a weight of . Males and females are almost identical externally. Their bodies are streamlined like
marine mammal Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They are an informal group, unified only by their reli ...
s and their robust build allows them to pull heavy loads. A beaver
coat A coat typically is an outer garment for the upper body as worn by either gender for warmth or fashion. Coats typically have long sleeves and are open down the front and closing by means of buttons, zippers, hook-and-loop fasteners, toggles, a ...
has 12,000–23,000 hairs/cm2 (77,000–148,000 per in2) and functions to keep the animal warm, to help it float in water, and to protect it against predators.
Guard hairs Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...
are long and typically reddish brown, but can range from yellowish brown to nearly black; while the
underfur Fur is a thick growth of hair that covers the skin of mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an insulating blanket t ...
is long and dark gray. Beavers
molt In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
every summer. Beavers have large skulls and powerful chewing muscles. They have four chisel-shaped incisors they keep growing throughout their lives. The incisors are covered in a thick enamel colored orange or reddish-brown by iron compounds. The lower incisors have roots that are almost as long as the entire lower jaw. Beavers have one premolar and three molars on all four sides of the jaws, adding up to 20 teeth. The molars have meandering ridges for grinding woody material. The eyes, ears and nostrils are arranged so that they can remain above water when the rest of the body submerges. The nostrils and ears have valves that close underwater while nictitating membranes cover the eyes. To protect the
larynx The larynx (), commonly called the voice box, is an organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal inlet is about ...
and
trachea The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...
from water flow, the
epiglottis The epiglottis is a leaf-shaped flap in the throat that prevents food and water from entering the trachea and the lungs. It stays open during breathing, allowing air into the larynx. During swallowing, it closes to prevent aspiration of food int ...
is contained within the nasal cavity instead of the throat. In addition, the back of the tongue can rise and create a waterproof seal. A beaver's lips can close behind the incisors, preventing water from entering their mouths as they cut and bite onto things while submerged. The beaver's front feet are dexterous, allowing them to grasp and manipulate objects and food, as well as dig. The hind feet are larger and have webbing between the toes, and the second innermost toe has a "double nail" used for grooming. Beavers can swim at ; only their webbed hind feet are used while the front feet fold under the chest. On the surface, the hind limbs thrust one after the other while underwater, they move at the same time. Beavers are awkward on land but can move quickly when they feel threatened. They can carry objects while walking on their hind legs. The beaver's distinctive tail consists of a conical, muscular, hairy base; and a flat, scaly end that makes up two-thirds of the appendage. The tail has multiple functions; it provides support for the animal when it is upright (such as when chewing down a tree), acts as a rudder when it is swimming and stores fat for winter. It also has a countercurrent blood vessel system which allows the animal to lose heat in warm temperatures and retain heat in cold temperatures. The beaver's sex organs are inside the body, and the male's penis has a cartilaginous
baculum The baculum (also penis bone, penile bone, or ''os penis'', ''os genitale'' or ''os priapi'') is a bone found in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the ...
. They have only one opening, a
cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
, for reproduction, scent-marking, defecation and urination. The cloaca evolved secondarily, as mammals have lost this feature, and may reduce the area vulnerable to infection in dirty water. The beaver's intestine is six times longer than its body, and the
caecum The cecum or caecum is a pouch within the peritoneum that is considered to be the beginning of the large intestine. It is typically located on the right side of the body (the same side of the body as the appendix, to which it is joined). The w ...
is double the volume of its stomach. Microorganisms in the caecum allow them to process around 30 percent of the
cellulose Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...
they eat. A beaver defecates in the water, leaving behind balls of sawdust. Female beavers have four
mammary glands A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands are arranged in organs such as the breasts in prima ...
; these produce milk with 19 percent fat, higher than in other rodents. Beavers have two pairs of glands, castor sacs, which are part of the urethra, and
anal gland Anal may refer to: Related to the anus *Related to the anus of animals: ** Anal fin, in fish anatomy ** Anal vein, in insect anatomy ** Anal scale, in reptile anatomy *Related to the human anus: ** Anal sex, a type of sexual activity involving s ...
s. The castor sacs secrete
castoreum Castoreum is a yellowish exudate from the castor sacs of mature beavers. Beavers use castoreum in combination with urine to scent mark their territory. Both beaver sexes have a pair of castor sacs and a pair of anal glands, located in two cavities ...
, a liquid substance used mainly for marking territory. Anal glands produce an oily substance which the beaver uses as a waterproof ointment for its coat. The substance plays a role in individual and family recognition. Anal secretions are darker in females than males among Eurasian beavers, while the reverse is true for the North American species. Compared to many other rodents, a beaver's brain has a
hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...
that is much smaller than the
cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. In ...
; this indicates a relatively advanced brain with higher intelligence. The
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...
is large, allowing the animal to move within a three-dimensional space (such as underwater) similar to tree-climbing squirrels. The
neocortex The neocortex, also called the neopallium, isocortex, or the six-layered cortex, is a set of layers of the mammalian cerebral cortex involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, sp ...
is devoted mainly to
touch In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It is ...
and hearing. Touch is more advanced in the lips and hands than the
whiskers Vibrissae (; singular: vibrissa; ), more generally called Whiskers, are a type of stiff, functional hair used by mammals to touch, sense their environment. These hairs are finely specialised for this purpose, whereas other types of hair are c ...
and tail. Vision in the beaver is comparably poor, and the beaver eye cannot see as well underwater as that of an
otter Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the Mustelidae family, which also includes wea ...
. Beavers have a good sense of smell, which they use for inspecting scent marks, food and other individuals, and for detecting land predators. Beavers can hold their breath for as long as 15 minutes. However, they typically remain underwater for no more than five or six minutes. Dives typically last less than 30 seconds and are usually no more than deep. When diving, their heart rate decreases to 60 beats per minute, only half its normal beat, and blood flow is directed more to the brain. A beaver's body also has a high tolerance for carbon dioxide. When surfacing, the animal can replace 75 percent of the air in its lungs in one breath, compared to 15 percent for a human.


Distribution and status

The
IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...
of mammals lists both beaver species as
least concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...
. The North American beaver is widespread throughout most of the United States and Canada and can be found in northern Mexico. The species was introduced to Finland in 1937 (and then spread to northwestern Russia) and to
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla G ...
, Patagonia, in 1946. The introduced population in Finland has been moving closer to the habitat of the Eurasian beaver as of 2019. Historically, the North American beaver was trapped and nearly extirpated because its fur was highly sought after. Protections have allowed the beaver population on the continent to rebound to an estimated 6–12million by the late 20th century; still far lower than the originally estimated 60–400million North American beavers before the days of the fur trade. The introduced population in Tierra del Fuego is estimated at 35,000–50,000 individuals as of 2016. The Eurasian beaver's range historically included much of Eurasia, but was decimated by hunting by the early 20th century. In Europe, beavers were reduced to fragmented populations in the
Rhône The Rhône ( , ; wae, Rotten ; frp, Rôno ; oc, Ròse ) is a major river in France and Switzerland, rising in the Alps and flowing west and south through Lake Geneva and southeastern France before discharging into the Mediterranean Sea. At Ar ...
of France, the
Elbe The Elbe (; cs, Labe ; nds, Ilv or ''Elv''; Upper and dsb, Łobjo) is one of the major rivers of Central Europe. It rises in the Giant Mountains of the northern Czech Republic before traversing much of Bohemia (western half of the Czech Repu ...
in Germany, southern Norway, the
Neman The Neman, Nioman, Nemunas or MemelTo bankside nations of the present: Lithuanian: be, Нёман, , ; russian: Неман, ''Neman''; past: ger, Memel (where touching Prussia only, otherwise Nieman); lv, Nemuna; et, Neemen; pl, Niemen; ...
river and
Dnieper } The Dnieper () or Dnipro (); , ; . is one of the major transboundary rivers of Europe, rising in the Valdai Hills near Smolensk, Russia, before flowing through Belarus and Ukraine to the Black Sea. It is the longest river of Ukraine and B ...
Basin in Belarus and the
Voronezh Voronezh ( rus, links=no, Воро́неж, p=vɐˈronʲɪʂ}) is a city and the administrative centre of Voronezh Oblast in southwestern Russia straddling the Voronezh River, located from where it flows into the Don River. The city sits on the ...
river in Russia with combined numbers estimated at 1,200 individuals. The beaver has since recolonized parts of its former range aided by conservation policies and reintroductions. Beaver populations now range across western, central and eastern Europe,
western Russia European Russia (russian: Европейская Россия, russian: европейская часть России, label=none) is the western and most populated part of Russia. It is geographically situated in Europe, as opposed to the cou ...
and the
Scandinavian Peninsula The Scandinavian Peninsula ( sv, Skandinaviska halvön; no, Den skandinaviske halvøy (Bokmål) or nn, Den skandinaviske halvøya; fi, Skandinavian niemimaa) is a peninsula located in Northern Europe, which roughly comprises the mainlands ...
. Beginning in 2009, beavers have been reintroduced successfully to parts of Great Britain. In 2020, the total Eurasian beaver population in Europe was estimated at over one million. Small native populations are also present in Mongolia and northwestern China; their numbers were estimated at 150 and 700 respectively as of 2016. Under New Zealand's
Hazardous Substances and New Organisms Act 1996 The Hazardous Substances and New Organisms Act (HSNO) is an Act of Parliament passed in New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North I ...
, beavers are classed as a "prohibited new organism" preventing them from being introduced into the country.


Ecology

Beavers live in
freshwater ecosystems Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be ...
such as rivers, streams, lakes and ponds. Water is the most important part of beaver habitat; they swim and dive in it, and it provides them a refuge from land predators, restricts access to their homes and allows them to move building objects more easily. Beavers prefer to use slower moving streams, typically with a
gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gradi ...
or steepness of one percent, though they have been recorded using streams with gradients as high as 15 percent. Beavers are found in wider streams more than narrower ones. They also prefer areas with no regular flooding and may abandon a location for years after a significant flood. Beavers typically select flat landscapes with diverse vegetation close to the water. North American beavers prefer trees being or less from the water, but will roam several hundred meters to find more. Beavers have also been recorded in mountainous areas. Dispersing beavers will use certain habitats temporarily before finding their ideal home. These include small streams, temporary swamps, ditches and backyards. These sites lack important resources, so the animals keep moving. Beavers have settled increasingly at or near human-made environments, including agricultural areas,
suburbs A suburb (more broadly suburban area) is an area within a metropolitan area, which may include commercial and mixed-use, that is primarily a residential area. A suburb can exist either as part of a larger city/urban area or as a separate ...
,
golf courses A golf course is the grounds on which the sport of golf is played. It consists of a series of holes, each consisting of a tee box, a fairway, the rough and other hazards, and a green with a cylindrical hole in the ground, known as a "cup". Th ...
and shopping malls. Beavers have a
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
and a
generalist A generalist is a person with a wide array of knowledge on a variety of subjects, useful or not. It may also refer to: Occupations * a physician who provides general health care, as opposed to a medical specialist; see also: ** General pract ...
diet. During the spring and summer, they mainly feed on herbaceous plant material such as leaves, roots, herbs, ferns, grasses,
sedges The Cyperaceae are a family of graminoid (grass-like), monocotyledonous flowering plants known as sedges. The family is large, with some 5,500 known species described in about 90 genera, the largest being the "true sedges" genus ''Carex'' wit ...
,
water lilies ''Water Lilies'' (or ''Nymphéas'', ) is a Serial imagery, series of approximately 250 oil paintings by French Impressionism, Impressionist Claude Monet (1840–1926). The paintings depict his Fondation Monet in Giverny, flower garden at Fond ...
, water shields, rushes and
cattails ''Typha'' is a genus of about 30 species of monocotyledonous flowering plants in the family Typhaceae. These plants have a variety of common names, in British English as bulrush or reedmace, in American English as reed, cattail, or punks, in A ...
. During the fall and winter, they eat more bark and
cambium A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...
of woody plants; tree and shrub species used include
aspen Aspen is a common name for certain tree species; some, but not all, are classified by botanists in the section ''Populus'', of the ''Populus'' genus. Species These species are called aspens: *'' Populus adenopoda'' – Chinese aspen (China ...
,
birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech-oak family Fagaceae. The genus ''Betula'' contains 30 ...
,
oak An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
,
dogwood ''Cornus'' is a genus of about 30–60 species of woody plants in the family Cornaceae, commonly known as dogwoods, which can generally be distinguished by their blossoms, berries, and distinctive bark. Most are deciduous trees or shrub ...
,
willow Willows, also called sallows and osiers, from the genus ''Salix'', comprise around 400 speciesMabberley, D.J. 1997. The Plant Book, Cambridge University Press #2: Cambridge. of typically deciduous trees and shrubs, found primarily on moist s ...
and
alder Alders are trees comprising the genus ''Alnus'' in the birch family Betulaceae. The genus comprises about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few sp ...
. There is some disagreement about why beaver select specific woody plants; some research has shown that beaver more frequently select species which are more easily digested, while others suggest beaver principally select forage based upon size. Beavers may
cache Cache, caching, or caché may refer to: Places United States * Cache, Idaho, an unincorporated community * Cache, Illinois, an unincorporated community * Cache, Oklahoma, a city in Comanche County * Cache, Utah, Cache County, Utah * Cache Count ...
their food for the winter, piling up wood in the deepest part of their pond where it cannot be reached by other browsers. This is known as a "raft" the top of which becomes frozen creating a "cap". The animal accesses the raft by swimming under the ice. Many populations of Eurasian beaver do not make rafts but forage on land during winter. Beavers usually live up to 10 years.
Felid Felidae () is the family of mammals in the order Carnivora colloquially referred to as cats, and constitutes a clade. A member of this family is also called a felid (). The term "cat" refers both to felids in general and specifically to the dom ...
s,
canid Canidae (; from Latin, ''canis'', "dog") is a biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamilies found within the ...
s and
bears Bears are carnivoran mammals of the family Ursidae. They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats throughout the North ...
may prey upon them. Beavers are protected from predators when in their lodges and prefer to stay near water. Their parasites include the bacteria ''
Francisella tularensis ''Francisella tularensis'' is a pathogenic species of Gram-negative coccobacillus, an aerobic bacterium. It is nonspore-forming, nonmotile, and the causative agent of tularemia, the pneumonic form of which is often lethal without treatment. It is ...
'', which causes
tularemia Tularemia, also known as rabbit fever, is an infectious disease caused by the bacterium ''Francisella tularensis''. Symptoms may include fever, skin ulcers, and enlarged lymph nodes. Occasionally, a form that results in pneumonia or a throat infe ...
; the protozoan ''
Giardia duodenalis ''Giardia duodenalis'', also known as ''Giardia intestinalis'' and ''Giardia lamblia'', is a flagellated parasitic microorganism of the genus ''Giardia'' that colonizes the small intestine, causing a diarrheal condition known as giardiasis. The ...
'', which causes
giardiasis Giardiasis is a parasitic disease caused by ''Giardia duodenalis'' (also known as ''G. lamblia'' and ''G. intestinalis''). Infected individuals who experience symptoms (about 10% have no symptoms) may have diarrhea, abdominal pain, and weight los ...
(beaver fever); and the beaver beetle and
mites Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...
of the genus '' Schizocarpus''. They have also been recorded with the
rabies virus Rabies virus, scientific name ''Rabies lyssavirus'', is a neurotropic virus that causes rabies in humans and animals. Rabies transmission can occur through the saliva of animals and less commonly through contact with human saliva. ''Rabies lyss ...
.


Infrastructure

Beavers need trees and shrubs as building material for
dams A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, ...
, which impound flowing water to create a pond for them to live in, and lodges, which act as shelters and refuges from predators and the elements. Without such material, beavers dig burrows into a
bank A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets. Because ...
to live. Construction begins in late summer or early fall, and they repair them whenever needed. Beavers can cut down trees wide or less in under 50 minutes. Thicker trees, at wide or more, may not fall for hours. When chewing down a tree, beavers switch between biting with the left and right side of the mouth. Tree branches are then cut and carried to their destination with the powerful jaw and neck muscles. Other building materials, like mud and rocks, are held by the forelimbs and tucked between the chin and chest. Beaver start building dams when they hear running water, and the sound of a leak in a dam triggers them to repair it. To build a dam, beavers stack up relatively long and thick logs between the banks and facing opposite directions. Heavy rocks hold down the poles, with grass packed between them. Beavers continue to pile on more material until the dam slopes in a direction facing upstream. Dams can range in height from to tall and can stretch from to several hundred meters long. Beaver dams are more effective in trapping and slowly leaking water than man-made concrete dams. Lake-dwelling beavers do not need to build dams. Beavers make two types of lodges: bank lodges and open-water lodges. Bank lodges are burrows dug along the shore and covered in sticks. The more complex freestanding, open-water lodges are built over a platform of piled-up sticks. The lodge is mostly sealed with mud except for a hole at the top which acts as an air vent. Both types are accessed by underwater entrances. The above-water space inside the lodge is known as the "living chamber" and a "dining area" may exist close to the water entrance. Families routinely clean out old plant material inside the lodge and bring in new ones. North American beavers build more open-water lodges than Eurasian beavers. Beaver lodges built by new settlers are typically small and sloppy. More experienced families can build structures with height of and around (above water). One sturdy enough to withstand the coming winter can be finished in just two nights. Both lodge types can be present at a beaver site. During the summer, beavers tend to use the bank lodges to keep cool. They use open-water lodges during the winter. The air vent provides ventilation, and new carbon dioxide can empty out in an hour. The lodge remains consistent in both oxygen and carbon dioxide levels from season to season. Beavers in some areas will dig canals connected to their ponds. The canals fill up with groundwater and give beavers access and easier transport of resources, as well as allow them to escape predators. These canals can stretch up to wide, deep and over long. It has been hypothesized that beavers' canals are not only transportation routes but an extension of their "
central place Central Place is a mixed-use development in Arlington, Virginia, consisting primarily of Central Place Tower (headquarters of Gartner) to the south, and a residential tower to the north, with a plaza between them. The office tower is home to Vir ...
" around the lodge and/or food cache. As they drag wood across the land, beavers leave behind trails or "slides", which they reuse when moving new material.


Environmental effects

The beaver works as an
ecosystem engineer An ecosystem engineer is any species that creates, significantly modifies, maintains or destroys a habitat. These organisms can have a large impact on species richness and landscape-level heterogeneity of an area. As a result, ecosystem enginee ...
and
keystone species A keystone species is a species which has a disproportionately large effect on its natural environment relative to its abundance, a concept introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaini ...
as its activities can have a great impact on the landscape and
biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...
of an area. Aside from humans, few other extant animals appear to do more to shape their environment. When building dams, beavers alter the paths of streams and rivers allowing for the creation of extensive
wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (anoxic) processes prevailing, especially in the soils. The ...
habitats. In one study, beavers were associated with large increases in open-water areas. When beavers returned to an area, 160% more open-water was available during droughts than in previous years when they were absent. Beaver dams also lead to higher
water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...
s, both in mineral soil environments and in wetlands such as
peatlands A mire, peatland, or quagmire is a wetland area dominated by living peat-forming plants. Mires arise because of incomplete decomposition of organic matter, usually litter from vegetation, due to water-logging and subsequent anoxia. All types ...
. In peatlands particularly, their dams stabilize the constantly changing water levels, leading to greater
carbon storage Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up o ...
. Beaver ponds, and the wetlands that succeed them, remove sediments and pollutants from waterways, and can stop the loss of important soils. These ponds can increase the
productivity Productivity is the efficiency of production of goods or services expressed by some measure. Measurements of productivity are often expressed as a ratio of an aggregate output to a single input or an aggregate input used in a production proces ...
of freshwater ecosystems by accumulating
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
in sediments. Beaver activity can affect the temperature of the water. In northern latitudes, ice thaws earlier in the warmer beaver-dammed waters. Beavers may contribute to
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...
. In Arctic areas, the floods they create can cause
permafrost Permafrost is ground that continuously remains below 0 °C (32 °F) for two or more years, located on land or under the ocean. Most common in the Northern Hemisphere, around 15% of the Northern Hemisphere or 11% of the global surface ...
to thaw, releasing methane into the atmosphere. As wetlands are formed and
riparian A riparian zone or riparian area is the interface between land and a river or stream. Riparian is also the proper nomenclature for one of the terrestrial biomes of the Earth. Plant habitats and communities along the river margins and banks ar ...
habitats enlarged, aquatic plants colonize the newly available watery habitat. One study in the
Adirondacks The Adirondack Mountains (; a-də-RÄN-dak) form a massif in northeastern New York with boundaries that correspond roughly to those of Adirondack Park. They cover about 5,000 square miles (13,000 km2). The mountains form a roughly circular d ...
found that beaver engineering leads an over 33 percent increase in
herbaceous plant Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition of t ...
diversity along the water edge. Another study in semiarid eastern Oregon found that the width of riparian vegetation on stream banks increased several-fold as beaver dams watered previously dry terraces adjacent to the stream. Riparian ecosystems in arid areas appear to sustain more plant life when beaver dams are present. Beaver ponds act as a refuge for water bank plants during
wildfires A wildfire, forest fire, bushfire, wildland fire or rural fire is an unplanned, uncontrolled and unpredictable fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identif ...
and provide them with enough moisture to resist such fires. Introduced beavers at Tierra del Fuego have been responsible for destroying the indigenous forest. Unlike trees in North America, many trees in South America cannot grow back after being cut down. Beaver activity impacts
communities A community is a Level of analysis, social unit (a group of living things) with commonality such as place (geography), place, Norm (social), norms, religion, values, Convention (norm), customs, or Identity (social science), identity. Communiti ...
of aquatic invertebrates. Damming typically leads to an increase of slow or motionless water species, like
dragonflies A dragonfly is a flying insect belonging to the infraorder Anisoptera below the order Odonata. About 3,000 extant species of true dragonfly are known. Most are tropical, with fewer species in temperate regions. Loss of wetland habitat threa ...
,
oligochaetes Oligochaeta () is a subclass of animals in the phylum Annelida, which is made up of many types of aquatic and terrestrial worms, including all of the various earthworms. Specifically, oligochaetes comprise the terrestrial megadrile earthworms ...
,
snails A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastrop ...
and
mussels Mussel () is the common name used for members of several families of bivalve mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,0 ...
, to the detriment of Lotic ecosystems, rapid water species like black flies, stoneflies and Hydropsychidae, net-spinning caddisflies. Beaver floodings create more dead trees, providing more habitat for terrestrial invertebrates like ''Drosophila'' flies and bark beetles, which live and breed in dead wood. The presence of beavers can increase wild salmon and trout populations, and the average size of these fish. These species use beaver habitats for spawning, overwintering, feeding and as havens from changes in water flow. The positive effects of beaver dams on fish appear to outweigh the negative effects, such as blocking of migration. Beaver ponds have been shown to be beneficial to frog populations by protecting areas for larvae to mature in warm water. The stable waters of beaver ponds also provide ideal habitat for freshwater turtles. Beavers help waterfowl by creating increased areas of water. The widening of the riparian zone associated with beaver dams has been shown to increase the abundance and diversity of birds favoring the water edge, an impact that may be especially important in semi-arid climates. Fish-eating birds use beaver ponds for foraging, and in some areas certain species appear more frequently where beavers were active than at sites with no beaver activity. In a study of Wyoming streams and rivers, watercourses with beavers had 75 times as many ducks as those without. As trees are drowned by rising beaver impoundments, they become ideal habitat for woodpeckers, which carve cavities that may be later used by other bird species. Beaver-caused ice thawing in northern latitudes allows Canada geese to nest earlier. Other semi-aquatic mammals, such as European water vole, water voles, muskrats, minks and otters will shelter in beaver lodges. Beaver modifications to streams in Poland create habitats favorable to bat species that hunt at the water surface and use moderate vegetation litter. Large herbivores such as some deer species benefit from beaver activity as they can access vegetation from fallen trees and ponds.


Behavior

Beavers are mainly nocturnality, nocturnal and Crepuscular animal, crepuscular and spend the daytime in their shelters. In northern latitudes, beaver activity is decoupled from the Circadian rhythm, 24-hour cycle during the winter and may last as much as 29 hours. They do not hibernate during winter, and spend much of their time in their lodges.


Family life

The core of beaver social organization is the family, which is composed of an adult male and an adult female in a Pair bond, monogamous pair and their offspring. Beaver families can have as many as ten members; groups about this size require multiple lodges. Mutual grooming and play fighting maintains bonds between family members, and aggression between them is uncommon. Adult beavers mate with their partners, though partner replacement appears to be common. A beaver that loses its partner will wait for another one to come by. Estrus cycles began in late December and peak in mid-January. Females may have two to four estrus cycles per season; each lasting 12–24 hours. The pair typically mate in the water and to a lesser extent in the lodge, for half a minute to three minutes. Up to four young or kits are born in spring and summer, after a three or four-month gestation. Newborn beavers are precocial with a full fur coat and can open their eyes within days. Their mother is the primary caretaker, while their father maintains the territory. Older siblings from a previous litter also play a role. After they are born, the kits spend the next first month or two in the lodge. Kits suckle for as long as three months but can eat solid food within their second week and rely on their parents and older siblings to bring it to them. Eventually, beaver kits explore outside the lodge and forage on their own but may follow an older relative and hold on to their backs. After their first year, young beavers help their families with construction. Beavers sexually mature around 1.5–3 years. They become independent at two years old, but remain with their parents for an extra year or more during times of food shortage, high population density, or drought.


Territories and spacing

Beavers typically disperse from their parental colonies during the spring or when the winter snow melts. They often travel less than , but long-distance dispersals are not uncommon when previous colonizers have already exploited local resources. Beavers are able to travel greater distances when free-flowing water is available. Individuals may meet their mates during the dispersal stage and the pair travel together. It may take them weeks or months to reach their final destination; longer distances may require several years. Beavers establish and defend
territories A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or an ...
along the banks of their ponds, which may be in length. Beavers mark their territories by constructing scent mounds made of mud and litter and scented with castoreum. Those with many territorial neighbors create more scent mounds. Scent marking increases in spring during the dispersal of yearlings to deter interlopers. Beavers are generally intolerant of intruders and fights may result in deep bites to the sides, rump and tail. They exhibit a behavior known as the "dear enemy effect". A territory-holder will investigate and become familiar with the scents of its neighbors and react more aggressively to the scents of strangers passing by. Beavers are also more tolerant of individuals that are their kin. They recognize them by using their keen sense of smell to detect differences in the composition of anal gland secretions. Anal gland secretion profiles are more similar among relatives than unrelated individuals.


Communication

Beavers within a family greet each other with whines. Kits will attract the attention of adults with mews, squeaks and cries. Defensive beavers produce a hissing growl and gnash their teeth. Tail slaps, which involve an animal hitting the water surface with its tail, serve as alarm signals warning other beavers of a potential threat. An adult's tail slap is more successful in alerting others, which then escape into the lodge or deeper water. Juveniles have not yet learned the proper use of a tail slap, and hence are normally ignored. Eurasian beavers have been recorded using a territorial "stick display". This involves individuals holding up a stick and bouncing in shallow water.


Interactions with humans

Beavers sometimes come into conflict with humans over land use; the individual beavers being labeled a "nuisance beaver". Beavers can damage crops, timber stocks, roads, ditches, gardens and pastures via gnawing, eating, digging or flooding. They occasionally Beaver attack, attack humans and domestic pets, particularly when infected with rabies, in defense of their territory, or when they feel threatened. Some of these attacks have been fatal, including at least one human death. Beavers can spread
giardiasis Giardiasis is a parasitic disease caused by ''Giardia duodenalis'' (also known as ''G. lamblia'' and ''G. intestinalis''). Infected individuals who experience symptoms (about 10% have no symptoms) may have diarrhea, abdominal pain, and weight los ...
by infecting surface waters, though outbreaks are more commonly caused by human activity. Flow devices, like beaver pipes, are used to manage beaver flooding, while fencing and hardwire cloth protects trees and shrubs from beaver damage. If necessary, hand tools, heavy equipment or explosives are used to remove dams. Hunting, trapping and relocation may be permitted as forms of population control and for removal of individuals. The governments of Argentina and Chile have authorized the trapping of invasive beavers in hopes of their elimination. The ecological importance of beavers has led to cities like Seattle designing their parks and Urban green space, green spaces to accommodate the animals. The Martinez beavers became famous in the mid-2000s for their role in improving the ecosystem of Alhambra Creek in Martinez, California. Zoos have displayed beavers since at least the 19th century, though not commonly. In captivity, beavers have been used for entertainment, fur harvesting and for reintroduction into the wild. Captive beavers require access to water, substrate for digging, and artificial shelters. Grey Owl, Archibald Stansfeld "Grey Owl" Belaney pioneered beaver conservation in the early 20th century. Belaney wrote several books and was first to professionally film them in their environment. In 1931 he moved to a log cabin in Prince Albert National Park, where he was the "caretaker of park animals", and raised a beaver pair and their four offspring.


Commercial use

Beavers have been hunted, trapped and exploited for their fur, meat and castoreum. Since they typically stayed in one place, trappers could easily find the animals and would kill entire families in a lodge. Pre-modern people appear to have thought that the castor sacs of the beaver were its testicles. Aesop's Fables describes beavers chewing off their testicles to preserve themselves from hunters, which is impossible because a beaver's testicles are internal; this myth has persisted for centuries. Beavers have historically been hunted and captured using Deadfall trap, deadfalls, Snare trap, snares, nets, bows and arrows, spears, clubs, firearms and leg-hold traps. Castoreum was used to lure the animals. Castoreum was used for a variety of medical purposes; Pliny the Elder promoted it as a treatment for stomach problems, flatulence, seizures, sciatica, vertigo and epilepsy. He stated it could stop hiccups when mixed with vinegar, toothaches if mixed with oil and administered into the ear opening on the same side as the tooth, and could be used as an antivenom. The substance has traditionally been prescribed to treat hysteria in women, which was believed to have been caused by a "toxic" womb. Castoreum's properties have been credited to the accumulation of salicylic acid from willow and aspen trees in the beaver's diet, and has a physiological effect very similar to aspirin. Today, the medical use of castoreum has declined and is limited mainly to homeopathy. The substance has also lent itself as an ingredient in perfumes and tinctures. Various Indigenous peoples of the Americas, Native American cultures have historically hunted beavers for food. Beaver meat was advantageous, being more calorie-rich and fattened than other red meats, and the animals remained plump in winter, when they were most hunted. The bones were used to make tools. In medieval Europe, the Catholic Church considered the beaver to be part mammal and part fish and allowed followers to eat the scaly, fishlike tail on meatless Fridays during Lent. Beaver tails were thus highly prized in Europe and were described by French naturalist Pierre Belon as tasting like a "nicely dressed eel". Beaver pelts were used to make Beaver hat, hats; felting, felters would remove the guard hairs. The number of pelts needed depended on the type of hat with Cavalier hat, Cavalier and Capotain, Puritan hats requiring more fur than top hats. In the late 16th century, Europeans began to North American fur trade, deal in North American furs due to the lack of taxes or tariffs on the continent and the decline of fur-bearers at home. Beaver pelts were valuable enough to cause or contribute to the Beaver Wars, King William's War and the French and Indian War. Fur traders were the main driver of the westward expansion of Europeans into the continent and make contact with the native peoples, who traded with the Europeans. The fur trade peaked between 1860 and 1870, when over 150,000 beaver pelts were purchased annually by the Hudson's Bay Company and fur companies in the US. The contemporary global fur trade is not as profitable due to conservation, Fur clothing#Anti-fur campaigns, anti-fur and animal rights campaigns.


In culture

The beaver has been used to represent productivity, trade, tradition, masculinity and respectability. References to the beaver's skills are reflected in everyday language. The English verb "to beaver" means working with great effort and being "as busy as a beaver", and a "beaver intellect" refers to a way of thinking that is both slow and honest. The name "beaver" also refers to the human vulva. Mythologies of the indigenous peoples of the Americas, Native American myths emphasize the beaver's skill and industriousness. In the mythology of the Haida people, Haida, beavers are descended from the Beaver-Woman, who built a dam on a stream next to their cabin while her husband was out hunting and gave birth to the first beavers. In a Cree story, the Great Beaver and its dam caused a Flood myth, world flood. Other tales involve beavers using their tree chewing skills against an enemy. Beavers have been featured as companions in some stories, including a Lakota people, Lakota tale where a young woman flees from her evil husband with the aid of her pet beaver. Europeans have traditionally thought of beavers as fantastical animals due to their amphibious nature. They depicted them as with exaggerated tusk-like teeth, dog- or pig-like bodies, fish tails and visible testicles. French cartographer Nicolas de Fer illustrated beavers building a dam at Niagara Falls; fantastically depicting them like human builders. Beavers have also appeared in literature such as in Dante Alighieri's ''Divine Comedy'' and in the writings of Athanasius Kircher, who wrote that on Noah's Ark the beavers were housed near a water-filled tub that was also used by mermaids and otters. The beaver has long been associated with Canada, appearing on the first pictorial postage stamp issued in the British North America, Canadian colonies in 1851—the so-called "Postage stamps and postal history of Canada, Three-Penny Beaver". It was declared the
national animal This is a list of countries that have officially designated one or more animals as their national animals. National animal {, class="wikitable sortable" ! Country ! Name of animal ! Scientific name (Latin name) ! class="unsortable", Picture ...
in 1975. The Nickel (Canadian coin), five-cent coin, the coat of arms of the Hudson's Bay Company and the logos for Parks Canada and Roots Canada use its image. Frank and Gordon are two fictional beavers that appeared in Bell Canada's advertisements between 2005 and 2008. However, the beaver's status as a rodent has made it controversial, and it was not chosen to be on the Arms of Canada in 1921. The beaver has commonly been used to represent Canada in political cartoons, typically to signify it as a friendly but relatively weak nation. In the United States, the beaver is the state animal of New York (state), New York and Oregon. It is also featured on the coat of arms of the London School of Economics.


References


Sources

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Further reading

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External links


Beaver Institute
Charity that supports beavers

How to identify beaver tracks in the wild {{featured article Beavers, Holarctic fauna Articles containing video clips Extant Miocene first appearances Taxa named by Carl Linnaeus Semiaquatic mammals