Terns are
seabird
Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same enviro ...
s in the
family
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 the family is to maintain the well-being of its members and of society. Idea ...
Laridae
Laridae is a family of seabirds in the order Charadriiformes that includes the gulls, terns, skimmers and kittiwakes. It includes around 100 species arranged into 22 genera. They are an adaptable group of mostly aerial birds found worldwide. ...
that have a worldwide distribution and are normally found near the
sea,
river
A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of w ...
s, or
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 p ...
s. Terns are treated as a subgroup of the family Laridae which includes
gull
Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century ...
s and
skimmers and consists of eleven
genera. They are slender, lightly built birds with long, forked tails, narrow wings, long bills, and relatively short legs. Most species are pale grey above and white below, with a contrasting black cap to the head, but the
marsh terns, the
Inca tern
The Inca tern (''Larosterna inca'') is a tern in the family Laridae. It is the only member of the genus ''Larosterna''.
This uniquely plumaged bird breeds on the coasts of Peru and Chile, and is restricted to the Humboldt Current. In 2021 a si ...
, and some
noddies have dark
plumage for at least part of the year. The sexes are identical in appearance, but young birds are readily distinguishable from adults. Terns have a non-breeding plumage, which usually involves a white forehead and much-reduced black cap.
Terns are long-lived birds and are relatively free from natural predators and
parasites
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson ha ...
; most species are declining in numbers due directly or indirectly to human activities, including habitat loss, pollution, disturbance, and predation by
introduced mammals. The
Chinese crested tern is in a
critical situation and three other species are classed as
endangered
An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and in ...
. International agreements provide a measure of protection, but adults and eggs of some species are still used for food in the tropics. The eggs of two species are eaten in the
West Indies
The West Indies is a subregion of North America, surrounded by the North Atlantic Ocean and the Caribbean Sea that includes 13 independent island countries and 18 dependencies and other territories in three major archipelagos: the Greate ...
because they are believed to have
aphrodisiac
An aphrodisiac is a substance that increases sexual desire, sexual attraction, sexual pleasure, or sexual behavior. Substances range from a variety of plants, spices, foods, and synthetic chemicals. Natural aphrodisiacs like cannabis or cocai ...
properties.
Description
Terns range in size from the
least tern
The least tern (''Sternula antillarum'') is a species of tern that breeds in North America and locally in northern South America. It is closely related to, and was formerly often considered conspecific with, the little tern of the Old World. Ot ...
, at in length and weighing ,
[Maehr & Kale (2005) p. 111.][Olsen & Larsson (1995) p. 136.] to the
Caspian tern
The Caspian tern (''Hydroprogne caspia'') is a species of tern, with a subcosmopolitan but scattered distribution. Despite its extensive range, it is monotypic of its genus, and has no accepted subspecies. The genus name is from Ancient Greek ' ...
at , .
[Harrison (1988) p. 368.] They are longer-billed, lighter-bodied, and more streamlined than gulls, and their long tails and long narrow wings give them an elegance in flight. Male and female plumages are identical, although the male can be 2–5% larger than the female and often has a relatively larger bill. Sea terns have deeply forked tails, and at least a shallow "V" is shown by all other species.
[ The noddies (genera ''Anous'', ''Procelsterna'' and ''Gygis'') have unusual notched-wedge shaped tails, the longest tail feathers being the middle-outer, rather than the central or outermost.][Harrison (1988) pp. 387–390.][Hutton & Drummond (2011) p. 226.] Although their legs are short, terns can run well. They rarely swim, despite having webbed feet, usually landing on water only to bathe.[
The majority of sea terns have light grey or white body plumage as adults, with a black cap to the head. The legs and bill are various combinations of red, orange, yellow, or black depending on species. The pale plumage is conspicuous from a distance at sea, and may attract other birds to a good feeding area for these fish-eating species. When seen against the sky, the white underparts also help to hide the hunting bird from its intended prey. The Inca tern has mainly dark plumage, and three species that mainly eat insects, the black tern, ]white-winged tern
The white-winged tern, or white-winged black tern (''Chlidonias leucopterus'' or ''Chlidonias leucoptera''), is a species of tern in the family Laridae. It is a small species generally found in or near bodies of fresh water across much of the wo ...
, and black-bellied tern
The black-bellied tern (''Sterna acuticauda'') is a tern found near large rivers in the Indian subcontinent, its range extending from Pakistan, Nepal and India to Myanmar. It has become very scarce in the eastern part of its range and the Intern ...
, have black underparts in the breeding season. The ''Anous'' noddies have dark plumage with a pale head cap. The reason for their dark plumage is unknown, but it has been suggested that in tropical areas, where food resources are scarce, the less conspicuous colouration makes it harder for other noddies to detect a feeding bird. Plumage type, especially the head pattern, is linked to the phylogeny
A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...
of the terns, and the pale-capped, dark-bodied noddies are believed to have diverged earlier than the other genera from an ancestral white-headed gull, followed by the partially black-headed '' Onychoprion'' and ''Sternula
''Sternula'' is a genus of small white tern
Terns are seabirds in the family Laridae that have a worldwide distribution and are normally found near the sea, rivers, or wetlands. Terns are treated as a subgroup of the family Laridae whi ...
'' groupings.[
Juvenile terns typically have brown- or yellow-tinged upperparts, and the feathers have dark edges that give the plumage a scaly appearance. They have dark bands on the wings and short tails. In most species, the subsequent ]moult
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 ...
does not start until after migration, the plumage then becoming more like the adult, but with some retained juvenile feathers and a white forehead with only a partial dark cap. By the second summer, the appearance is very like the adult, and full mature plumage is usually attained by the third year. After breeding, terns moult into a winter plumage, typically showing a white forehead. Heavily worn or aberrant plumages such as melanism
The term melanism refers to black pigment and is derived from the gr, μελανός. Melanism is the increased development of the dark-colored pigment melanin in the skin or hair.
Pseudomelanism, also called abundism, is another variant of ...
and albinism
Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino.
Varied use and interpretation of the term ...
are much rarer in terns than in gulls.
Voice
Terns have a wide repertoire of vocalisations. For example, the common tern
The common tern (''Sterna hirundo'') is a seabird in the family Laridae. This bird has a circumpolar distribution, its four subspecies breeding in temperate and subarctic regions of Europe, Asia and North America. It is strongly migrator ...
has a distinctive alarm
An alarm device is a mechanism that gives an audible, visual or other kind of alarm signal to alert someone to a problem or condition that requires urgent attention.
Alphabetical musical instruments
Etymology
The word ''alarm'' comes from t ...
, ''kee-yah'', also used as a warning to intruders, and a shorter ''kyar'', given as an individual takes flight in response to a more serious threat; this quietens the usually noisy colony while its residents assess the danger. Other calls include a down-slurred ''keeur'' given when an adult is approaching the nest with a fish, and a ''kip'' uttered during social contact.[Hume (1993) pp. 68–75.] Parents and chicks can locate one another by call,[Burton (1985) p. 123.] and sibling
A sibling is a relative that shares at least one parent with the subject. A male sibling is a brother and a female sibling is a sister. A person with no siblings is an only child.
While some circumstances can cause siblings to be raised separa ...
s also recognise each other's vocalisations from about the twelfth day after hatching, which helps to keep the brood together.
Vocal differences reinforce species separation between closely related birds such as the least and little tern
The little tern (''Sternula albifrons'') is a seabird of the family Laridae. It was formerly placed into the genus ''Sterna'', which now is restricted to the large white terns. The genus name is a diminutive of '' Sterna'', "tern". The specific ' ...
s, and can help humans distinguish similar species, such as common and Arctic terns, since flight calls are unique to each species.[Constantine (2006) pp. 73–77.][
]
Taxonomy
The bird order Charadriiformes
Charadriiformes (, from ''Charadrius'', the type genus of family Charadriidae) is a diverse order of small to medium-large birds. It includes about 390 species and has members in all parts of the world. Most charadriiform birds live near water an ...
contains 18 coastal seabird and wader
245px, A flock of Dunlins and Red knots">Red_knot.html" ;"title="Dunlins and Red knot">Dunlins and Red knots
Waders or shorebirds are birds of the order Charadriiformes commonly found wikt:wade#Etymology 1, wading along shorelines and mudflat ...
families
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 the family is to maintain the well-being of its members and of society. Ideal ...
. Within the order, the terns form a lineage with the gull
Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century ...
s, and, less closely, with the skimmers, skua
The skuas are a group of predatory seabirds with seven species forming the genus ''Stercorarius'', the only genus in the family Stercorariidae. The three smaller skuas, the long-tailed skua, the Arctic skua, and the pomarine skua are called ...
s, and auks. Early authors such as Conrad Gessner
Conrad Gessner (; la, Conradus Gesnerus 26 March 1516 – 13 December 1565) was a Swiss physician, naturalist, bibliographer, and philologist. Born into a poor family in Zürich, Switzerland, his father and teachers quickly realised his tale ...
, Francis Willughby
Francis Willughby (sometimes spelt Willoughby, la, Franciscus Willughbeius) FRS (22 November 1635 – 3 July 1672) was an English ornithologist and ichthyologist, and an early student of linguistics and games.
He was born and raised at ...
, and William Turner did not clearly separate terns from gulls,[ but ]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 ...
recognised the distinction in his 1758 '' Systema Naturae'', placing the gulls in the genus '' Larus'' and the terns in ''Sterna''. He gave ''Sterna'' the description ''rostrum subulatum'', " awl-shaped bill", referring to the long, pointed bills typical of this group of birds, a feature that distinguishes them from the thicker-billed gulls.[Linnaeus (1758) p. 84.][Jobling (2010) p. 338.] Behaviour and morphology
Morphology, from the Greek and meaning "study of shape", may refer to:
Disciplines
* Morphology (archaeology), study of the shapes or forms of artifacts
* Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
suggest that the terns are more closely related to the gulls than to the skimmers or skuas, and although Charles Lucien Bonaparte created the family Sternidae for the terns in 1838, for many years they were considered to be a subfamily, Sterninae, of the gull family, Laridae. Relationships between various tern species, and between the terns and the other Charadriiformes, were formerly difficult to resolve because of a poor fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
record and the misidentification of some finds.[Gochfeld & Burger (1996) pp. 624–645.]
Following gene
In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
tic research in the early twenty-first century, the terns were historically treated as a separate family: Sternidae. Most terns were formerly treated as belonging to one large genus, ''Sterna
''Sterna'' is a genus of terns in the bird family Laridae. The genus used to encompass most "white" terns indiscriminately, but mtDNA sequence comparisons have recently determined that this arrangement is paraphyletic. It is now restricted to t ...
'', with just a few dark species placed in other genera; in 1959, only the noddies and the Inca tern
The Inca tern (''Larosterna inca'') is a tern in the family Laridae. It is the only member of the genus ''Larosterna''.
This uniquely plumaged bird breeds on the coasts of Peru and Chile, and is restricted to the Humboldt Current. In 2021 a si ...
were excluded from ''Sterna''. A recent analysis of DNA sequences
A nucleic acid sequence is a succession of bases signified by a series of a set of five different letters that indicate the order of nucleotides forming alleles within a DNA (using GACT) or RNA (GACU) molecule. By convention, sequences are us ...
supported the splitting of ''Sterna'' into several smaller genera. One study of part of the cytochrome b
Cytochrome b within both molecular and cell biology, is a protein found in the mitochondria of eukaryotic cells. It functions as part of the electron transport chain and is the main subunit of transmembrane cytochrome bc1 and b6f complexes.
F ...
gene sequence found a close relationship between terns and a group of waders in the suborder Thinocori. These results are in disagreement with other molecular and morphological studies, and have been interpreted as showing either a large degree of molecular convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...
between the terns and these waders, or the retention of an ancient genotype.[
The word "stearn" was used for these birds in ]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 settlers in the mid-5th c ...
as early as the eighth century, and appears in the poem '' The Seafarer'', written in the ninth century or earlier. Variants such as "tearn" occurred by the eleventh century, although the older form lingered on in Norfolk dialect
East Anglian English is a dialect of English spoken in East Anglia, primarily in or before the mid-20th century. East Anglian English has had a very considerable input into modern Estuary English, which has largely replaced it. However, it has r ...
for several centuries.[Hume (1993) pp. 12–13.] As now, the term was used for the inland black tern
The black tern (''Chlidonias niger'') is a small tern generally found in or near inland water in Europe, Western Asia and North America. As its name suggests, it has predominantly dark plumage. In some lights it can appear blue in the breeding se ...
as well as the marine species.[Jobling (2010) p. 365.][Lockwood (1984) pp. 147, 153.] Some authorities consider "tearn" and similar forms to be variants of "stearn",[ while others derive the English words from Scandinavian equivalents such as Danish and Norwegian ''terne'' or Swedish ''tärna'', and ultimately from ]Old Norse
Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and their overseas settlemen ...
''þerna''.[Merriam-Webster (2014)] Linnaeus adopted "stearn" or "sterna" (which the naturalist William Turner had used in 1544 as a Latinisation of an English word, presumably "stern", for the black tern)[Turner (1544), p. 78.] or a North Germanic
The North Germanic languages make up one of the three branches of the Germanic languages—a sub-family of the Indo-European languages—along with the West Germanic languages and the extinct East Germanic languages. The language group is also r ...
equivalent for his genus name ''Sterna''.[Linnaeus (1758) p. 155.]
Species
The cladogram
A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
shows the relationships between the tern genera, and the currently recognised species, based on mitochondrial DNA studies, are listed below:[
In addition to extant species, the fossil record includes a ]Miocene
The Miocene ( ) is the first epoch (geology), 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 mea ...
palaeospecies, '' Sterna milne-edwardsii''.
The genera ''Anous'', ''Procelsterna'' and ''Gygis'' are collectively known as noddies, the ''Chlidonias'' species are the marsh terns,[ and all other species comprise the sea terns.][Barlow ''et al.'' (1987) p. 212.][Perrins & Arlott (1987) p. 130.]
Distribution and habitat
Terns have a worldwide distribution, breeding on all continents including Antarctica. The northernmost and southernmost breeders are the Arctic tern and Antarctic tern
The Antarctic tern (''Sterna vittata'') is a seabird in the family Laridae. It ranges throughout the southern oceans and is found on small islands around Antarctica as well as on the shores of the mainland. Its diet consists primarily of small fis ...
respectively.[Harrison (1988) pp. 370–371.] Many terns breeding in temperate zones are long-distance migrants, and the Arctic tern probably sees more annual daylight than any other animal as it migrates from its northern breeding grounds to Antarctic waters, a return journey of more than . A common tern that hatched in Sweden and was found dead five months later on Stewart Island, New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, must have flown at least .[Newton (2010) pp. 150–151.] Actual flight distances are, of course, much greater than the shortest possible route. Arctic terns from Greenland were shown by radio geolocation
Geopositioning, also known as geotracking, geolocalization, geolocating, geolocation, or geoposition fixing, is the process of determining or estimating the geographic position of an object.
Geopositioning yields a set of geographic coordinates ...
to average on their annual migrations.
Most terns breed on open sandy or rocky areas on coasts and islands. The yellow-billed, large-billed, and black-fronted terns breed only on rivers, and common, least and little terns also sometimes use inland locations. The marsh terns, Trudeau's tern and some Forster's tern
Forster's tern (''Sterna forsteri'') is a tern in the family Laridae. The genus name ''Sterna'' is derived from Old English "stearn", "tern", and ''forsteri'' commemorates the naturalist Johann Reinhold Forster.
It breeds inland in North America ...
s nest in inland marshes. The black noddy
The black noddy or white-capped noddy (''Anous minutus'') is a seabird from the family Laridae. It is a medium-sized species of tern with black plumage and a white cap. It closely resembles the lesser noddy (''Anous tenuirostris'') with which it ...
and the white tern
The white tern or common white tern (''Gygis alba'') is a small seabird found across the tropical oceans of the world. It is sometimes known as the fairy tern, although this name is potentially confusing as it is also the common name of '' Sternu ...
nest above ground level on cliffs or in trees. Migratory terns move to the coast after breeding, and most species winter near land, although some marine species, like the Aleutian tern, may wander far from land. The sooty tern is entirely oceanic when not breeding, and healthy young birds are not seen on land for up to five years after fledging until they return to breed. They lack waterproof plumage, so they cannot rest on the sea. Where they spend the years prior to breeding is unknown.[
]
Behaviour
The terns are birds of open habitats that typically breed in noisy colonies
In modern parlance, 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 '' metropolitan state'' ...
and lay their eggs on bare ground with little or no nest material. Marsh terns construct floating nests from the vegetation in their wetland habitats, and a few species build simple nests in trees, on cliffs or in crevices. The white tern
The white tern or common white tern (''Gygis alba'') is a small seabird found across the tropical oceans of the world. It is sometimes known as the fairy tern, although this name is potentially confusing as it is also the common name of '' Sternu ...
, uniquely, lays its single egg on a bare tree branch. Depending on the species, one to three eggs make up the clutch. Most species feed on fish caught by diving from flight, but the marsh terns are insect-eaters, and some large terns will supplement their diet with small land vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s. Many terns are long-distance migrants, and the Arctic tern may see more daylight in a year than any other animal.
Breeding
Terns are normally monogamous, although trios or female-female pairings have been observed in at least three species. Most terns breed annually and at the same time of year, but some tropical species may nest at intervals shorter than 12 months or asynchronously. Most terns become sexually mature when aged three, although some small species may breed in their second year. Some large sea terns, including the sooty and bridled terns, are four or older when they first breed. Terns normally breed in colonies
In modern parlance, 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 '' metropolitan state'' ...
, and are site-faithful if their habitat is sufficiently stable. A few species nest in small or dispersed groups, but most breed in colonies of up to a few hundred pairs, often alongside other seabirds such as gulls or skimmers.[ Large tern species tend to form larger colonies,][ which in the case of the sooty tern can contain up to two million pairs. Large species nest very close together and sit tightly, making it difficult for aerial predators to land among them. Smaller species are less closely packed and ]mob
Mob or MOB may refer to:
Behavioral phenomena
* Crowd
* Smart mob, a temporary self-structuring social organization, coordinated through telecommunication
Crime and law enforcement
* American Mafia, also known as the Mob
* Irish Mob, a US crimin ...
intruders. Peruvian
Peruvians ( es, peruanos) are the citizens of Peru. There were Andean and coastal ancient civilizations like Caral, which inhabited what is now Peruvian territory for several millennia before the Spanish conquest of Peru, Spanish conquest in th ...
and Damara terns have small dispersed colonies and rely on the cryptic plumage of the eggs and young for protection.[
The male selects a ]territory
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 a ...
, which he defends against conspecifics, and re-establishes a pair bond
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of offspring and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is freque ...
with his mate or attracts a new female if necessary. Courtship involves ritualised flight and ground displays, and the male often presents a fish to his partner. Most species have little or no nest, laying the eggs onto bare ground, but Trudeau's tern, Forster's tern and the marsh terns construct floating nests from the vegetation in their wetland habitats. Black and lesser noddies build nests of twigs, feathers and excreta on tree branches, and brown
Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing or painting, brown is usually made by combining the colors orange and black. In the RGB color model us ...
, blue
Blue is one of the three primary colours in the RYB colour model (traditional colour theory), as well as in the RGB (additive) colour model. It lies between violet and cyan on the spectrum of visible light. The eye perceives blue when ...
, and grey noddies make rough platforms of grass and seaweed on cliff ledges, in cavities or on other rocky surfaces.[Watling (2003) pp. 206–207.] The Inca tern nests in crevices, caves and disused burrows, such as that of a Humboldt penguin
The Humboldt penguin (''Spheniscus humboldti'') is a medium-sized penguin. It resides in South America, its range mainly contains most of coastal Peru. Its nearest relatives are the African penguin, the Magellanic penguin and the Galápagos pen ...
.[ The white tern is unique in that it lays its single egg on a bare tree branch.]
Tropical species usually lay just one egg, but two or three is typical in cooler regions if there is an adequate food supply. The time taken to complete the clutch varies, but for temperate species incubation takes 21–28 days.[ The eggs of most gulls and terns are brown
with dark splotches, so they are difficult for predators to spot on the beach.][ The ]precocial
In biology, altricial species are those in which the young are underdeveloped at the time of birth, but with the aid of their parents mature after birth. Precocial species are those in which the young are relatively mature and mobile from the mome ...
chicks fledge in about four weeks after hatching. Tropical species take longer because of the poorer food supply. Both parents incubate the eggs and feed the chicks, although the female does more incubating and less fishing than her partner.[ Young birds migrate with the adults.][ Terns are generally long-lived birds, with individuals typically returning for 7–10 breeding seasons. Maximum known ages include 34 for an Arctic tern and 32 for a sooty. Although several other species are known to live in captivity for up to 20 years, their greatest recorded ages are underestimates because the birds can outlive their ]rings
Ring may refer to:
* Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry
* To make a sound with a bell, and the sound made by a bell
:(hence) to initiate a telephone connection
Arts, entertainment and media Film and ...
.[ Interbreeding between tern species is rare, and involves closely related species when it occurs. Hybrids recorded include common tern with roseate, Sandwich with lesser-crested, and black with white-winged.][Olsen & Larsson (1995) p. 10.]
Feeding
Most terns hunt fish by diving, often hovering first, and the particular approach technique used can help to distinguish similar species at a distance.[Hume & Pearson (1993) pp. 54–55.] Sea terns often hunt in association with porpoises or predatory fish, such as bluefish
The bluefish (''Pomatomus saltatrix'') is the only extant species of the family Pomatomidae. It is a marine pelagic fish found around the world in temperate and subtropical waters, except for the northern Pacific Ocean. Bluefish are known as ta ...
, tuna
A tuna is a saltwater fish that belongs to the 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 (max len ...
or bonitos, since these large marine animals drive the prey to the surface. Sooty terns feed at night as the fish rise to the surface, and are believed to sleep on the wing since they become waterlogged easily. Terns of several species will feed on invertebrate
Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...
s, following the plough or hunting on foot on mudflats.[ The marsh terns normally catch insects in the air or pick them off the surface of fresh water. Other species will sometimes use these techniques if the opportunity arises.][Svensson ''et al.'' (2009) p. 206.] An individual tern's foraging efficiency increases with its age.[Burger J; Gochfeld M "Laridae, Sternidae and Rynchopidae" in Steele ''et al.'' (2001) p. 1469–1480.]
The gull-billed tern
The gull-billed tern (''Gelochelidon nilotica''), formerly ''Sterna nilotica'', is a tern in the family Laridae. It is widely distributed and breeds in scattered localities in Europe, Asia, northwest Africa, and the Americas. The Australian gull ...
is an opportunist predator, taking a wide variety of prey from marine, freshwater and terrestrial habitats. Depending on what is available it will eat small crabs, fish, crayfish, grasshoppers and other large insects, lizards and amphibians. Warm-blooded
Warm-blooded is an informal term referring to animal species which can maintain a body temperature higher than their environment. In particular, homeothermic species maintain a stable body temperature by regulating metabolic processes. The onl ...
prey includes mice and the eggs and chicks of other beach-breeding birds; least terns, little terns and members of its own species may be victims. The greater crested tern
The greater crested tern Retrieved 28 February 2012 (''Thalasseus bergii''), also called crested tern or swift tern, is a tern in the family Laridae that nests in dense colonies on coastlines and islands in the tropical and subtropical Old World ...
will also occasionally catch unusual vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
species such as agamid lizards and green sea turtle hatchlings, and follows trawlers for discards.
The eyes of terns cannot accommodate under water, so they rely on accurate sighting from the air before they plunge-dive.[ Like other seabirds that feed at the surface or dive for food, terns have red oil droplets in the ]cones
A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex.
A cone is formed by a set of line segments, half-lines, or lines conn ...
of their retina
The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
s;[ birds that have to look through an air/water interface have more deeply coloured carotenoid ]pigment
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compou ...
s in the oil drops than other species.[Varela, F J; Palacios, A G; Goldsmith T M "Color vision in birds" in Ziegler & Bischof (1993) pp. 77–94.] The pigment also improves visual contrast and sharpens distance vision, especially in hazy conditions,[Sinclair (1985) pp. 88–100.] and helps terns to locate shoals of fish, although it is uncertain whether they are sighting the phytoplankton on which the fish feed, or other feeding birds.[Lythgoe (1979) pp. 180–183.] The red colouring reduces ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
sensitivity, which in any case is an adaptation more suited to terrestrial feeders like the gulls, and this protects the eye from UV damage.[Coles (2007) p. 30.]
File:Sternula albifrons 2 - Little Swanport.jpg, Little tern
The little tern (''Sternula albifrons'') is a seabird of the family Laridae. It was formerly placed into the genus ''Sterna'', which now is restricted to the large white terns. The genus name is a diminutive of '' Sterna'', "tern". The specific ' ...
in flight showing the forked tail
File:Gull billed Tern I IMG 9309.jpg, The gull-billed tern
The gull-billed tern (''Gelochelidon nilotica''), formerly ''Sterna nilotica'', is a tern in the family Laridae. It is widely distributed and breeds in scattered localities in Europe, Asia, northwest Africa, and the Americas. The Australian gull ...
will sometimes prey on the chicks and young of other terns
File:Chlidonias hybrida 2 (Marek Szczepanek).jpg, The whiskered tern is an insect-eating marsh tern
Predators and parasites
The inaccessibility of many tern colonies gave them a measure of protection from mammalian predators, especially on islands, but introduced species
An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived ther ...
brought by humans can seriously affect breeding birds. These can be predators such as foxes, raccoon
The raccoon ( or , ''Procyon lotor''), sometimes called the common raccoon to distinguish it from other species, is a mammal native to North America. It is the largest of the procyonid family, having a body length of , and a body weight of ...
s, cat
The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...
s and rats, or animals that destroy the habitat, including rabbits, goat
The goat or domestic goat (''Capra hircus'') is a domesticated species of goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a member of the a ...
s and pig
The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...
s.[ Problems arise not only on formerly mammal-free islands, as in New Zealand, but also where an alien ]carnivore
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...
, such as the American mink
The American mink (''Neogale vison'') is a semiaquatic species of mustelid native to North America, though human intervention has expanded its range to many parts of Europe, Asia and South America. Because of range expansion, the American mink i ...
in Scotland
Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...
, presents an unfamiliar threat.[Hume (1993) pp. 112–119.]
Adult terns may be hunted by owl
Owls are birds from the order Strigiformes (), which includes over 200 species of mostly solitary and nocturnal birds of prey typified by an upright stance, a large, broad head, binocular vision, binaural hearing, sharp talons, and feathers a ...
s and raptors, and their chicks and eggs may be taken by herons, crow
A crow is a bird of the genus '' Corvus'', or more broadly a synonym for all of ''Corvus''. Crows are generally black in colour. The word "crow" is used as part of the common name of many species. The related term "raven" is not pinned scientifica ...
s or gulls.[ Less obvious nest predators include ]ruddy turnstone
The ruddy turnstone (''Arenaria interpres'') is a small cosmopolitan wading bird, one of two species of turnstone in the genus ''Arenaria''.
It is now classified in the sandpiper family Scolopacidae but was formerly sometimes placed in the plov ...
s in the Arctic, and gull-billed terns in little tern colonies. Adults may be robbed of their catch by avian kleptoparasites such as frigatebird
Frigatebirds are a family of seabirds called Fregatidae which are found across all tropical and subtropical oceans. The five extant species are classified in a single genus, ''Fregata''. All have predominantly black plumage, long, deeply forked ...
s, skuas, other terns or large gulls.[Harrison (1988) pp. 320–323.]
External parasite
Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has ...
s include chewing lice of the genus '' Saemundssonia'', feather lice
A bird louse is any chewing louse (small, biting insects) of order Phthiraptera which parasitizes warm-blooded animals, especially birds. Bird lice may feed on feathers, skin, or blood. They have no wings, and their biting mouth parts distingui ...
and fleas such as '' Ceratophyllus borealis''.[Rothschild & Clay (1953) p. 82, 130.] Lice are often host specific, and the closely related common and Arctic terns carry quite different species.[Rothschild & Clay (1953) p. 135.] Internal parasites include the crustacean
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
'' Reighardia sternae'', and tapeworms
Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of ...
such as ''Ligula intestinalis
''Ligula intestinalis'' is a cestoda, tapeworm of fish, fish-eating birds and copepods, with species from each group featuring in its complex Biological life cycle, life cycle. ''Ligula intestinalis'' is a parasite that changes its intermediate ...
'' and members of the genera '' Diphyllobothrium'' and '' Schistocephalus''.[Rothschild & Clay (1953) p. 194–197.] Terns are normally free of blood parasites, unlike gulls that often carry ''Haemoproteus
''Haemoproteus'' is a genus of alveolates that are parasitic in birds, reptiles and amphibians. Its name is derived from Greek: ''Haima'', "blood", and ''Proteus'', a sea god who had the power of assuming different shapes. The name ''Haemoprot ...
'' species. An exception is the brown noddy, which sometimes harbours protozoa of that genus. In 1961 the common tern was the first wild bird species identified as being infected with avian influenza, the H5N3 variant being found in an outbreak involving South African birds. Several species of terns have been implicated as carriers of West Nile virus
West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family '' Flaviviridae'', from the genus '' Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The v ...
.[Takken & Knols (2007) p. 137–140.]
Relationships with humans
Terns and their eggs have long been eaten by humans and island colonies were raided by sailors on long voyages since the eggs or large chicks were an easily obtained source of protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
. Eggs are still illegally harvested in southern Europe, and adults of wintering birds are taken as food in West Africa and South America. The roseate tern is significantly affected by this hunting, with adult survival 10% lower than would otherwise be expected. In the West Indies, the eggs of roseate and sooty terns are believed to be aphrodisiac
An aphrodisiac is a substance that increases sexual desire, sexual attraction, sexual pleasure, or sexual behavior. Substances range from a variety of plants, spices, foods, and synthetic chemicals. Natural aphrodisiacs like cannabis or cocai ...
s, and are disproportionately targeted by egg collectors. Tern skins and feathers have long been used for making items of clothing such as capes and hats, and this became a large-scale activity in the second half of the nineteenth century when it became fashionable to use feathers in hatmaking. This trend started in Europe but soon spread to the Americas and Australia. White was the preferred colour, and sometimes wings or entire birds were used.
Terns have sometimes benefited from human activities, following the plough or fishing boats for easy food supplies, although some birds get trapped in nets or swallow plastic. Fishermen looked for feeding tern flocks, since the birds could lead them to fish shoals. Overfishing of small fish such as sand eel
Sand eel or sandeel is the common name used for a considerable number of species of fish. While they are not true eels, they are eel-like in their appearance and can grow up to in length. Many species are found off the western coasts of Europe ...
s can lead to steep declines in the colonies relying on these prey items. More generally, the loss or disruption to tern colonies caused by human activities has caused declines in many species.[ Pollution has been a problem in some areas, and in the 1960s and 1970s ]DDT
Dichlorodiphenyltrichloroethane, commonly known as DDT, is a colorless, tasteless, and almost odorless crystalline chemical compound, an organochloride. Originally developed as an insecticide, it became infamous for its environmental impacts. ...
caused egg loss through thinning of the shells. In the 1980s, organochloride
An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class (alkanes with one or more hydrogens substituted by chlo ...
s caused severe declines in the Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lak ...
area of the US.[ Because of their sensitivity to pollutants, terns are sometimes used as indicators of contamination levels.][
Habitat enhancements used to increase the breeding success of terns include floating nest platforms for black, common and Caspian terns,] and artificial islands created for a number of different species. More specialised interventions include providing nest boxes for roseate terns, which normally nest in the shelter of tallish vegetation, and using artificial eelgrass Eelgrass is a common name for several plants and may refer to:
* ''Zostera'', marine eelgrass
* ''Vallisneria'', freshwater eelgrass
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