Arctic Tern
Encyclopedia
The Arctic Tern is a seabird
of the tern
family
Sternidae. This bird
has a circumpolar breeding distribution covering the Arctic
and sub-Arctic regions of Europe
, Asia
, and North America
(as far south as Brittany and Massachusetts
). The species
is strongly migratory
, seeing two summers each year as it migrates from its northern breeding grounds along a winding route to the oceans around Antarctica and back, a round trip of about 70,900 km (c. 44,300 miles) each year. This is by far the longest regular migration by any known animal. The Arctic Tern flies as well as glides through the air, performing almost all of its tasks in the air. It nests once every one to three years (depending on its mating cycle); once it has finished nesting it takes to the sky for another long southern migration.
Arctic Terns are medium-sized birds. They have a length of 33–39 cm (13–15 in) and a wingspan
of 76–85 cm (26–30 in). They are mainly grey and white plumaged, with a red beak (as long as the head, straight, with pronounced gonys) and feet, white forehead, a black nape and crown (streaked white), and white cheeks. The grey mantle is 305 mm, and the scapulae are fringed brown, some tipped white. The upper wing is grey with a white leading edge, and the collar is completely white, as is the rump. The deeply forked tail is whitish, with grey outer webs. The hindcrown to the ear-coverts is black.
Arctic Terns are long-lived birds, with many reaching thirty years of age. They eat mainly fish and small marine invertebrate
s. The species is abundant, with an estimated one million individuals. While the trend in the number of individuals in the species as a whole is not known, exploitation in the past has reduced this bird's numbers in the southern reaches of its range.
. It can be found in coastal regions in cooler temperate parts of North America and Eurasia
during the northern
summer. While wintering during the southern
summer, it can be found at sea, reaching the southern edge of the Antarctic ice.
The species' range encompasses an area of approximately ten million square kilometers.
The Arctic Tern is famous for its migration; it flies from its Arctic breeding grounds to the Antarctic and back again each year. This 19000 km (11,806.1 mi) journey each way (measured point to point) ensures that this bird sees two summers per year and more daylight than any other creature on the planet. One example of this bird's remarkable long-distance flying abilities involves an Arctic Tern ringed
as an unfledged chick on the Farne Islands
, Northumberland
, UK, in the northern summer of 1982, which reached Melbourne
, Australia
, in October 1982, a sea journey of over 22000 km (13,670.2 mi) in just three months from fledging. Another example is that of a chick ringed in Labrador
, Canada
, on 23 July 1928. It was found in South Africa
four months later.
Research using tracking devices attached to the birds was published in January 2010 and showed that the above examples are in fact not unusual for the species; eleven Arctic Terns that bred in Greenland or Iceland each covered 70,900 km on average in a year, with a maximum of 81,600 km. The difference from previous estimates was because the birds were found to take a meandering course to take advantage of prevailing winds. The average Arctic Tern lives about twenty years, and will travel about 2.4 million km (1.5 million mi).
Arctic Terns usually migrate far offshore. Consequently, they are rarely seen from land outside the breeding season.
The Arctic Tern is a medium-sized bird around 33–36 cm (13–15 in) from the tip of its beak to the tip of its tail. The wingspan is 76–85 cm. The weight is 86–127 g (3.0–4.5 oz). The beak
is dark red, as are the short legs and webbed feet. Like most terns, the Arctic Tern has high aspect ratio wings
and a tail with a deep fork.
The adult plumage
is grey above, with a black nape and crown and white cheeks. The upperwings are pale grey, with the area near the wingtip being translucent. The tail is white, and the underparts pale grey. Both sexes are similar in appearance. The winter plumage is similar, but the crown is whiter and the bills are darker.
Juveniles differ from adults in their black bill and legs, "scaly" appearing wings, and mantle with dark feather tips, dark carpal wing bar, and short tail streamers. During their first summer, juveniles also have a whiter forecrown.
The species has a variety of calls; the two most common being the alarm call, made when possible predators (such as humans or other mammal
s) enter the colonies, and the advertising call. The advertising call is social in nature, made when returning to the colony and during aggressive encounters between individuals. It is unique to each individual tern and as such it serves a similar role to the bird song
of passerine
s, identifying individuals. Eight other calls have been described, from begging calls made by females during mating to attack calls made while swooping at intruders.
While the Arctic Tern is similar to the Common
and Roseate Tern
s, its colouring, profile, and call are slightly different. Compared to the Common Tern, it has a longer tail and mono-coloured bill, while the main differences from the Roseate are its slightly darker colour and longer wings. The Arctic Tern's call is more nasal and rasping than that of the Common, and is easily distinguishable from that of the Roseate.
This bird's closest relatives are a group of South Polar species, the South American
(Sterna hirundinacea), Kerguelen
(S. virgata), and Antarctic
(S. vittata) Terns. On the wintering grounds, the Arctic Tern can be distinguished from these relatives; the six-month difference in moult
is the best clue here, with Arctic Terns being in winter plumage during the southern summer. The southern species also do not show darker wingtips in flight.
The immature plumages of Arctic Tern were originally described as separate species, Sterna portlandica and Sterna pikei.
Breeding begins around the third or fourth year. Arctic Terns mate for life, and in most cases, return to the same colony each year. Courtship is elaborate, especially in birds nesting for the first time. Courtship begins with a so-called "high flight", where a female will chase the male to a high altitude and then slowly descend. This display is followed by "fish flights", where the male will offer fish to the female. Courtship on the ground involves strutting with a raised tail and lowered wings. After this, both birds will usually fly and circle each other.
_chick.jpg)
Both sexes agree on a site for a nest, and both will defend the site. During this time, the male continues to feed the female. Mating occurs shortly after this. Breeding takes place in colonies on coasts, islands and occasionally inland on tundra
near water. It often forms mixed flocks with the Common Tern
. It lays from one to three eggs
per clutch, most often two.
It is one of the most aggressive terns, fiercely defensive of its nest and young. It will attack humans and large predators, usually striking the top or back of the head. Although it is too small to cause serious injury, it is still capable of drawing blood. Other birds can benefit from nesting in an area defended by Arctic Terns.
The nest is usually a depression in the ground, which may or may not be lined with bits of grass or similar materials. The eggs are mottled and camouflaged. Both sexes share incubation duties. The young hatch after 22–27 days and fledge
after 21–24 days. If the parents are disturbed and flush from the nest frequently the incubation period could be extended to as long as 34 days.
When hatched, the chicks are downy
. Neither altricial
nor precocial
, the chicks begin to move around and explore their surroundings within one to three days after hatching. Usually, they do not stray far from the nest. Chicks are brooded by the adults for the first ten days after hatching. Both parents care for hatchlings. Chick diets always include fish, and parents selectively bring larger prey items to chicks than they eat themselves. Males bring more food than females. Feeding by the parents lasts for roughly a month before being weaned off slowly. After fledging, the juveniles learn to feed themselves, including the difficult method of plunge-diving. They will fly south to winter with the help of their parents.
Arctic Terns are long-lived birds that spend considerable time raising only a few young, and are thus said to be K-selected
. The maximum recorded life span
for the species is 34 years, although the average lifespan is about 20 years A study in the Farne Islands estimated an annual survival rate of 82%.
. In most cases, it eats small fish
or marine crustacean
s. Fish species comprise the most important part of the diet, and account for more of the biomass consumed than any other food. Prey species are immature (1–2 year old) shoaling species such as herring
, cod
, sandlances, and capelin
. Among the marine crustaceans eaten are amphipods, crab
s and krill
. Sometimes, these birds also eat molluscs, marine worms, or berries
, and on their northern breeding grounds, insect
s.
Arctic Terns sometimes dip down to the surface of the water to catch prey close to the surface. They may also chase insects in the air when breeding. It is also thought that Arctic Terns may, in spite of their small size, occasionally engage in kleptoparasitism
by swooping at birds so as to startle them into releasing their catches. Several species are targeted—conspecifics, other terns (like the Common Tern), and some auk
and grebe
species.
While nesting, Arctic Terns are vulnerable to predation by cats and other animals. Besides being a competitor for nesting sites, the larger Herring Gull
steals eggs and hatchlings. Camouflaged eggs help prevent this, as do isolated nesting sites. While feeding, skua
s, gulls, and other tern species will often harass the birds and steal their food. They often form mixed colonies with other terns, such as Common
and Sandwich Terns.
Arctic Terns are considered threatened or species of concern in certain states. They are also among a species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds
applies. The species reduced population in New England
in the late nineteenth-century because of hunting for the millinery trade. Exploitation continues today in western Greenland
, where the species has reduced population greatly since 1950.
At the southern part of their range, the Arctic Tern has been reducing in numbers. Much of this is due to lack of food. However, most of these birds' range is extremely remote, with no apparent trend in the species as a whole.
'Birdlife International has considered the species to be at lower risk since 1988, believing that there are approximately one million individuals around the world.
, Alderney
, and Faroe Islands
. Countries include Canada
, Finland
, Iceland
, and Cuba
.
Seabird
Seabirds are birds that have 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 environmental problems and feeding niches have resulted in similar adaptations...
of the tern
Tern
Terns are seabirds in the family Sternidae, previously considered a subfamily of the gull family Laridae . They form a lineage with the gulls and skimmers which in turn is related to skuas and auks...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Sternidae. This bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
has a circumpolar breeding distribution covering the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
and sub-Arctic regions of Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
, and North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
(as far south as Brittany and Massachusetts
Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...
). The species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
is strongly migratory
Bird migration
Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat or weather. Sometimes, journeys are not termed "true migration" because they are irregular or in only one direction...
, seeing two summers each year as it migrates from its northern breeding grounds along a winding route to the oceans around Antarctica and back, a round trip of about 70,900 km (c. 44,300 miles) each year. This is by far the longest regular migration by any known animal. The Arctic Tern flies as well as glides through the air, performing almost all of its tasks in the air. It nests once every one to three years (depending on its mating cycle); once it has finished nesting it takes to the sky for another long southern migration.
Arctic Terns are medium-sized birds. They have a length of 33–39 cm (13–15 in) and a wingspan
Wingspan
The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...
of 76–85 cm (26–30 in). They are mainly grey and white plumaged, with a red beak (as long as the head, straight, with pronounced gonys) and feet, white forehead, a black nape and crown (streaked white), and white cheeks. The grey mantle is 305 mm, and the scapulae are fringed brown, some tipped white. The upper wing is grey with a white leading edge, and the collar is completely white, as is the rump. The deeply forked tail is whitish, with grey outer webs. The hindcrown to the ear-coverts is black.
Arctic Terns are long-lived birds, with many reaching thirty years of age. They eat mainly fish and small marine invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s. The species is abundant, with an estimated one million individuals. While the trend in the number of individuals in the species as a whole is not known, exploitation in the past has reduced this bird's numbers in the southern reaches of its range.
Distribution and migration
The Arctic Tern has a worldwide, circumpolar breeding distribution which is continuous; there are no recognized subspeciesSubspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
. It can be found in coastal regions in cooler temperate parts of North America and Eurasia
Eurasia
Eurasia is a continent or supercontinent comprising the traditional continents of Europe and Asia ; covering about 52,990,000 km2 or about 10.6% of the Earth's surface located primarily in the eastern and northern hemispheres...
during the northern
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
summer. While wintering during the southern
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
summer, it can be found at sea, reaching the southern edge of the Antarctic ice.
The species' range encompasses an area of approximately ten million square kilometers.
The Arctic Tern is famous for its migration; it flies from its Arctic breeding grounds to the Antarctic and back again each year. This 19000 km (11,806.1 mi) journey each way (measured point to point) ensures that this bird sees two summers per year and more daylight than any other creature on the planet. One example of this bird's remarkable long-distance flying abilities involves an Arctic Tern ringed
Bird ringing
Bird ringing or bird banding is a technique used in the study of wild birds, by attaching a small, individually numbered, metal or plastic tag to their legs or wings, so that various aspects of the bird's life can be studied by the ability to re-find the same individual later...
as an unfledged chick on the Farne Islands
Farne Islands
The Farne Islands are a group of islands off the coast of Northumberland, England. There are between 15 and 20 or more islands depending on the state of the tide. They are scattered about 2.5–7.5 km distant from the mainland, divided into two groups, the Inner Group and the Outer Group...
, Northumberland
Northumberland
Northumberland is the northernmost ceremonial county and a unitary district in North East England. For Eurostat purposes Northumberland is a NUTS 3 region and is one of three boroughs or unitary districts that comprise the "Northumberland and Tyne and Wear" NUTS 2 region...
, UK, in the northern summer of 1982, which reached Melbourne
Melbourne
Melbourne is the capital and most populous city in the state of Victoria, and the second most populous city in Australia. The Melbourne City Centre is the hub of the greater metropolitan area and the Census statistical division—of which "Melbourne" is the common name. As of June 2009, the greater...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, in October 1982, a sea journey of over 22000 km (13,670.2 mi) in just three months from fledging. Another example is that of a chick ringed in Labrador
Labrador
Labrador is the distinct, northerly region of the Canadian province of Newfoundland and Labrador. It comprises the mainland portion of the province, separated from the island of Newfoundland by the Strait of Belle Isle...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, on 23 July 1928. It was found in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
four months later.
Research using tracking devices attached to the birds was published in January 2010 and showed that the above examples are in fact not unusual for the species; eleven Arctic Terns that bred in Greenland or Iceland each covered 70,900 km on average in a year, with a maximum of 81,600 km. The difference from previous estimates was because the birds were found to take a meandering course to take advantage of prevailing winds. The average Arctic Tern lives about twenty years, and will travel about 2.4 million km (1.5 million mi).
Arctic Terns usually migrate far offshore. Consequently, they are rarely seen from land outside the breeding season.
Description and taxonomy
Beak
The beak, bill or rostrum is an external anatomical structure of birds which is used for eating and for grooming, manipulating objects, killing prey, fighting, probing for food, courtship and feeding young...
is dark red, as are the short legs and webbed feet. Like most terns, the Arctic Tern has high aspect ratio wings
Bird flight
Flight is the main mode of locomotion used by most of the world's bird species. Flight assists birds while feeding, breeding and avoiding predators....
and a tail with a deep fork.
The adult plumage
Plumage
Plumage refers both to the layer of feathers that cover a bird and the pattern, colour, and arrangement of those feathers. The pattern and colours of plumage vary between species and subspecies and can also vary between different age classes, sexes, and season. Within species there can also be a...
is grey above, with a black nape and crown and white cheeks. The upperwings are pale grey, with the area near the wingtip being translucent. The tail is white, and the underparts pale grey. Both sexes are similar in appearance. The winter plumage is similar, but the crown is whiter and the bills are darker.
The species has a variety of calls; the two most common being the alarm call, made when possible predators (such as humans or other mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s) enter the colonies, and the advertising call. The advertising call is social in nature, made when returning to the colony and during aggressive encounters between individuals. It is unique to each individual tern and as such it serves a similar role to the bird song
Bird song
Bird vocalization includes both bird calls and bird songs. In non-technical use, bird songs are the bird sounds that are melodious to the human ear. In ornithology and birding, songs are distinguished by function from calls.-Definition:The distinction between songs and calls is based upon...
of passerine
Passerine
A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...
s, identifying individuals. Eight other calls have been described, from begging calls made by females during mating to attack calls made while swooping at intruders.
While the Arctic Tern is similar to the Common
Common Tern
The Common Tern is a seabird of the tern family Sternidae. This bird has a circumpolar distribution, breeding in temperate and sub-Arctic regions of Europe, Asia and east and central North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. It is sometimes...
and Roseate Tern
Roseate Tern
The Roseate Tern is a seabird of the tern family Sternidae. This bird has a number of geographical races, differing mainly in bill colour and minor plumage details....
s, its colouring, profile, and call are slightly different. Compared to the Common Tern, it has a longer tail and mono-coloured bill, while the main differences from the Roseate are its slightly darker colour and longer wings. The Arctic Tern's call is more nasal and rasping than that of the Common, and is easily distinguishable from that of the Roseate.
This bird's closest relatives are a group of South Polar species, the South American
South American Tern
The South American Tern is a species of tern found in coastal regions of southern South America, including the Falkland Islands, ranging north to Peru and Brazil . It is generally the commonest tern in its range. It closely resembles the smaller, highly migratory Common Tern.-References:*...
(Sterna hirundinacea), Kerguelen
Kerguelen Tern
The Kerguelen Tern is a tern of the southern hemisphere.This seabird mainly breeds colonially in the Kerguelen Islands, as its common name implies. However, smaller colonies are also found in the Prince Edward Islands and Crozet Islands...
(S. virgata), and Antarctic
Antarctic Tern
The Antarctic Tern is a typical tern. It ranges throughout the southern oceans. It is very similar in appearance to the closely related Arctic Tern, but is stockier, and the wing tips are grey instead of blackish in flight...
(S. vittata) Terns. On the wintering grounds, the Arctic Tern can be distinguished from these relatives; the six-month difference in moult
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
is the best clue here, with Arctic Terns being in winter plumage during the southern summer. The southern species also do not show darker wingtips in flight.
The immature plumages of Arctic Tern were originally described as separate species, Sterna portlandica and Sterna pikei.
Reproduction
Tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...
near water. It often forms mixed flocks with the Common Tern
Common Tern
The Common Tern is a seabird of the tern family Sternidae. This bird has a circumpolar distribution, breeding in temperate and sub-Arctic regions of Europe, Asia and east and central North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. It is sometimes...
. It lays from one to three eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
per clutch, most often two.
Fledge
Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...
after 21–24 days. If the parents are disturbed and flush from the nest frequently the incubation period could be extended to as long as 34 days.
When hatched, the chicks are downy
Down feather
The down of birds is a layer of fine feathers found under the tougher exterior feathers. Very young birds are clad only in down. Powder down is a specialized type of down found only in a few groups of birds. Down is a fine thermal insulator and padding, used in goods such as jackets, bedding,...
. Neither altricial
Altricial
Altricial, meaning "requiring nourishment", refers to a pattern of growth and development in organisms which are incapable of moving around on their own soon after hatching or being born...
nor precocial
Precocial
In biology, the term precocial refers to species in which the young are relatively mature and mobile from the moment of birth or hatching. The opposite developmental strategy is called "altricial," where the young are born or hatched helpless. Extremely precocial species may be called...
, the chicks begin to move around and explore their surroundings within one to three days after hatching. Usually, they do not stray far from the nest. Chicks are brooded by the adults for the first ten days after hatching. Both parents care for hatchlings. Chick diets always include fish, and parents selectively bring larger prey items to chicks than they eat themselves. Males bring more food than females. Feeding by the parents lasts for roughly a month before being weaned off slowly. After fledging, the juveniles learn to feed themselves, including the difficult method of plunge-diving. They will fly south to winter with the help of their parents.
Arctic Terns are long-lived birds that spend considerable time raising only a few young, and are thus said to be K-selected
R/K selection theory
In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity or quality of offspring...
. The maximum recorded life span
Maximum life span
Maximum life span is a measure of the maximum amount of time one or more members of a population has been observed to survive between birth and death.Most living species have at least one upper limit on the number of times cells can divide...
for the species is 34 years, although the average lifespan is about 20 years A study in the Farne Islands estimated an annual survival rate of 82%.
Ecology and behaviour
The diet of the Arctic Tern varies depending on location and time, but is usually carnivorousCarnivore
A carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
. In most cases, it eats small fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
or marine crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. Fish species comprise the most important part of the diet, and account for more of the biomass consumed than any other food. Prey species are immature (1–2 year old) shoaling species such as herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, cod
Cod
Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...
, sandlances, and capelin
Capelin
The capelin or caplin, Mallotus villosus, is a small forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat a great deal of krill and other crustaceans...
. Among the marine crustaceans eaten are amphipods, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s and krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
. Sometimes, these birds also eat molluscs, marine worms, or berries
Berry
The botanical definition of a berry is a fleshy fruit produced from a single ovary. Grapes are an example. The berry is the most common type of fleshy fruit in which the entire ovary wall ripens into an edible pericarp. They may have one or more carpels with a thin covering and fleshy interiors....
, and on their northern breeding grounds, insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s.
Arctic Terns sometimes dip down to the surface of the water to catch prey close to the surface. They may also chase insects in the air when breeding. It is also thought that Arctic Terns may, in spite of their small size, occasionally engage in kleptoparasitism
Kleptoparasitism
Kleptoparasitism or cleptoparasitism is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food...
by swooping at birds so as to startle them into releasing their catches. Several species are targeted—conspecifics, other terns (like the Common Tern), and some auk
Auk
An auk is a bird of the family Alcidae in the order Charadriiformes. Auks are superficially similar to penguins due to their black-and-white colours, their upright posture and some of their habits...
and grebe
Grebe
A grebe is a member of the Podicipediformes order, a widely distributed order of freshwater diving birds, some of which visit the sea when migrating and in winter...
species.
While nesting, Arctic Terns are vulnerable to predation by cats and other animals. Besides being a competitor for nesting sites, the larger Herring Gull
American Herring Gull
The American Herring Gull or Smithsonian Gull is a large gull which breeds in North America. It is often treated as a subspecies of the European Herring Gull but is now regarded as a separate species by some authorities.Adults are white with gray back and wings, black wingtips with white spots,...
steals eggs and hatchlings. Camouflaged eggs help prevent this, as do isolated nesting sites. While feeding, skua
Skua
The skuas are a group of seabirds with about seven species forming the family Stercorariidae and the genus Stercorarius. The three smaller skuas are called jaegers in North America....
s, gulls, and other tern species will often harass the birds and steal their food. They often form mixed colonies with other terns, such as Common
Common Tern
The Common Tern is a seabird of the tern family Sternidae. This bird has a circumpolar distribution, breeding in temperate and sub-Arctic regions of Europe, Asia and east and central North America. It is strongly migratory, wintering in coastal tropical and subtropical regions. It is sometimes...
and Sandwich Terns.
Conservation status
AEWA
The Agreement on the Conservation of African-Eurasian Migratory Waterbirds is the largest of its kind developed so far under the Bonn Convention. It was concluded on 16 June 1995 at The Hague, the Netherlands and entered into force on 1 November 1999 after the required number of at least fourteen...
applies. The species reduced population in New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
in the late nineteenth-century because of hunting for the millinery trade. Exploitation continues today in western Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
, where the species has reduced population greatly since 1950.
At the southern part of their range, the Arctic Tern has been reducing in numbers. Much of this is due to lack of food. However, most of these birds' range is extremely remote, with no apparent trend in the species as a whole.
'Birdlife International has considered the species to be at lower risk since 1988, believing that there are approximately one million individuals around the world.
Cultural depictions
The Arctic Tern has appeared on the postage stamps of several countries and dependent territories. Territories include the Åland IslandsÅland Islands
The Åland Islands form an archipelago in the Baltic Sea. They are situated at the entrance to the Gulf of Bothnia and form an autonomous, demilitarised, monolingually Swedish-speaking region of Finland...
, Alderney
Alderney
Alderney is the most northerly of the Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide. The area is , making it the third-largest island of the Channel Islands, and the second largest in the Bailiwick...
, and Faroe Islands
Faroe Islands
The Faroe Islands are an island group situated between the Norwegian Sea and the North Atlantic Ocean, approximately halfway between Scotland and Iceland. The Faroe Islands are a self-governing territory within the Kingdom of Denmark, along with Denmark proper and Greenland...
. Countries include Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, and Cuba
Cuba
The Republic of Cuba is an island nation in the Caribbean. The nation of Cuba consists of the main island of Cuba, the Isla de la Juventud, and several archipelagos. Havana is the largest city in Cuba and the country's capital. Santiago de Cuba is the second largest city...
.
External links
- Arctic Tern videos, photos & sounds on the Internet Bird Collection
- Cornell Laboratory of Ornithology Species Account
- ARKive images