The Aleutian tern (''Onychoprion aleuticus'') is a
migratory bird
Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting b ...
living in the
subarctic region of the globe most of the year. It is frequently associated with the
Arctic tern, which it closely resembles. While both species have a black cap, the Aleutian tern may be distinguished by its white forehead (although juvenile
Arctic terns also have white foreheads). During
breeding season, the
Arctic terns have bright red bills, feet, and legs while those of the Aleutian terns are black.
''Onychoprion aleuticus'' has not been thoroughly studied yet. If its winter migratory range was completely unknown until the late 1980s; it is now known that many Aleutian terns spend the winter near the Equator in the western Pacific. The Aleutian tern breeds in wide-ranging coastal colonies only in
Alaska
Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S. ...
and eastern
Siberia
Siberia ( ; rus, Сибирь, r=Sibir', p=sʲɪˈbʲirʲ, a=Ru-Сибирь.ogg) is an extensive region, geographical region, constituting all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has been a ...
. Although Alaskan and Siberian populations are not well monitored, both are thought to be in significant decline.
Taxonomy
The Aleutian tern, ''Onychoprion aleuticus'' (Baird, 1869) is a bird in the family
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. ...
, a
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 ...
of
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
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 ...
that includes 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,
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 which includes gulls and skimmers and consists of e ...
s and
skimmers. The generic name is from
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
''onux'', "claw" or "nail", and ''prion'', "saw". The specific epithet ''aleuticus'' refers to the
Aleutian Islands
The Aleutian Islands (; ; ale, Unangam Tanangin,”Land of the Aleuts", possibly from Chukchi ''aliat'', "island"), also called the Aleut Islands or Aleutic Islands and known before 1867 as the Catherine Archipelago, are a chain of 14 large v ...
.
It was formerly named ''Sterna aleutica.
[Bridge, E. S.; Jones, A. W. & Baker, A. J. (2005)]
A phylogenetic framework for the terns (Sternini) inferred from mtDNA sequences: implications for taxonomy and plumage evolution
. ''Molecular Phylogenetics and Evolution'' 35: 459–469.''. Indeed, in his 1758 ''
Systema Naturae'',
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 ...
placed the terns in the genus ''Sterna''. However, a phylogenetic analysis found that the species in the ''Onychoprion'' clade, which includes ''O. aleuticus'', ''O. fuscatus'' (
Sooty tern), and ''O. anaethetus'' (
Bridled tern
The bridled tern (''Onychoprion anaethetus'') is a seabird of the family Laridae. It is a bird of the tropical oceans. The scientific name is from Ancient Greek. The genus comes from ' meaning "claw" or "nail", and , meaning "saw". The specific ...
), are related only distantly to the "typical" terns retained in a much-restricted ''Sterna''. Still, in broader terms the
genera ''
Onychoprion
''Onychoprion'', the "brown-backed terns", is a genus of seabirds in the family Laridae. The genus name is from Ancient Greek , "claw" or "nail", and , "saw".
Species
Although the genus was first described in 1832 by Johann Georg Wagler the four ...
'' and ''
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 ...
'' are sisters.
Relationships between various tern species, and between the terns and the other
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 ...
, 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.
Description
The Aleutian tern is medium-sized tern ( long), with a wingspan, a short pointed bill and a long, deeply forked tail.
It weighs 84–140 g (2.9–5.0 oz).
Plumage
Breeding adult and juvenile are the only plumages likely to be encountered in North America. Breeding adult (definitive alternate plumage) has a white forehead, a black cap, a mid-grey mantle with darkish grey underparts, and white rump and tail. Its underwing is whitish, with dark-tipped primaries and a diagnostic dark bar on the secondaries.
The Aleutian tern has a black bill as well as black legs. There are no significant differences between the male and the female.
The
plumage of the non-breeding adult (definitive basic plumage) is poorly known. It is thought to be similar to plumage of breeding adult. It has white underparts, a white speckled crown, and a gray tail with white sides. Whereas the forehead bar disappears in winter, the dark secondary bar remains.
Lee
described juveniles with a white collar, extensive white forehead, white underparts, and gray tail with white outer web of outer tail-feather. They usually do not have clear dark bar on their secondaries.
Molt strategies are very poorly known in Aleutian tern but are presumably similar to other medium-sized, northern-breeding, migratory terns such as much better-studied
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 ...
. The Aleutian tern exhibits a Complex Alternate Strategy:
Voice
The Aleutian tern is associated with different calls reported in the literature. Their call can be distinguished from 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 ...
ones, since it has a higher pitch and is characterized by a soft and rolling whistled tone.
The most distinctive sound is the choppy “''chif-chif-chu-ak''” described by Olsen and Larsson in 1995,
less harsh than the sustained note of the
Arctic tern. Another distinctive sound of the Aleutian tern is a prolonged "''whee-hee-hee-hee"'' stressed on the first syllable.
Aleutian terns also have a call that is similar to call of
Red-necked Phalarope
The red-necked phalarope (''Phalaropus lobatus''), also known as the northern phalarope and hyperborean phalarope, is a small wader. This phalarope breeds in the Arctic regions of North America and Eurasia. It is migratory, and, unusually for a ...
(''Phalaropus lobatus''), which is a short, sharp "''chit"''
'','' possibly uttered during social contact.
The Aleutian tern is generally silent while incubating.
Distribution and habitat
![Chukchi Sea map](https://upload.wikimedia.org/wikipedia/commons/5/5a/Chukchi_Sea_map.png)
During
breeding season, the colonies gather along Pacific coastlines of Alaska and Russia.
More precisely, breeding colonies have been located along the coast of Chukchi Sea (western Alaska), on the Seward Peninsula and Yukon-Kuskokwim River Delta along the Alaska Peninsula, in the Aleutian Island, in the Kodiak Archipelago, on the Kenai Peninsula and Copper River delta, and along the Gulf of Alaska.
The current worldwide minimum breeding population has been estimated at approximately 31 000 birds, with most colonies occurring in the Siberian region of Russia (25 602 birds in 89 colonies) and the remaining 18% occurring in Alaska (5 529 birds in 111 colonies). However, within the last decade, there have been reports of colony declines and disappearances at individual sites in Alaska.
A small population spends the Southern Spring and Summer on the east coast of Australia
This species is strongly
migratory, and although the wintering range is poorly known, it is believed to lie off Indonesia and Malaysia.
Small flocks of the species have been increasingly sighted in coastal areas around Hong Kong in spring and fall, around Singapore and Indonesia between October and April, and in coastal waters of Java, Bali and Sulawesi during December.
The regular appearance of Aleutian terns in fall off Hong Kong suggests one possible route for southbound migrants.
The Aleutian tern stands out from its congeners because it is the only species to show an annual migratory behaviour between a
subarctic breeding zone and tropical wintering areas in the South Pacific. Only a very small number of
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 ...
breeding in Alaska appear to have a connection to East Asia. In December 2017, they were spotted for the first time on
Australia's eastern coast.
Habitat
The Aleutian tern usually lives in partially vegetated sandy beaches and grassy
meadow
A meadow ( ) is an open habitat, or field, vegetated by grasses, herbs, and other non- woody plants. Trees or shrubs may sparsely populate meadows, as long as these areas maintain an open character. Meadows may be naturally occurring or arti ...
s, mossy
boglands and
marsh
A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found a ...
es, either on isolated rocky islands or along coasts, often near river mouths. The Aleutian tern is
pelagic
The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...
when it is not breeding.
Status
Trends in the Aleutian tern distribution indicates that overall, the species seems to undergo rapid declines over generations. Indeed, the numbers at known colonies in Alaska have declined 8.1% annually since 1960, which corresponds to 92.9% over three generations, with large colonies experiencing greater declines than small colonies.
The Aleutian tern has therefore been listed as a “Vulnerable” species. Precise factors of declines are unclear but likely include habitat modification,
predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
, egg harvesting and human
disturbance.
Moreover, wintering area in Southeast Asia could be related to breeding population declines because this region undergoes several ecological stresses from unregulated fishing, coastal development, and
pollution
Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, the ...
. Aleutian terns are very sensitive to disturbance at colonies and may seasonally or even permanently abandon their colonies in response to human disturbance.
Conservation
The Aleutian tern has been designated as a species of concern by several agencies and NGOs (
Alaska Department of Fish and Game
The Alaska Department of Fish and Game (ADF&G) is a department within the government of Alaska. ADF&G's mission is to protect, maintain, and improve the fish, game, and aquatic plant resources of the state, and manage their use and development in ...
,
Audubon Alaska,
U.S. Fish and Wildlife Service
The United States Fish and Wildlife Service (USFWS or FWS) is an agency within the United States Department of the Interior dedicated to the management of fish, wildlife, and natural habitats. The mission of the agency is "working with othe ...
,
The North American Waterbird Conservation Plan). In 2007, an Aleutian tern Working Group was organized in Alaska in order to examine the necessity to develop an accurate population estimation method and therefore prioritizing the management of the species and the identification of its migration pathway. In 2010, they began to deploy geolocators on Aleutians terns from colonies in
Alaska
Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S. ...
. The lack of data on breeding biology and ecological behaviours limits the development of
conservation
Conservation is the preservation or efficient use of resources, or the conservation of various quantities under physical laws.
Conservation may also refer to:
Environment and natural resources
* Nature conservation, the protection and managem ...
actions for the species. Further research should focus on the monitoring of populations and colonies in Alaska, Russia and South Pacific regions and the understanding of the main causes of the recent decline of the species.
Behaviour
Breeding and Parental Behaviour
Aleutian terns 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.
Pairs form on the breeding area, shortly after arrival. The pairs build the nest during the last half of May and first half of June, shortly before egg-laying.
The typical clutch size is 2 eggs (occasionally 1 or 3).
The nest is a shallow depression usually built on low vegetation such as mosses, lichens, field horsetail, cottongrass, hairgrass or coastal bluegrass.
Both parents incubate the eggs and feed the chicks, although the female does more
incubating and less fishing than her partner.
Aleutian terns are reported to spend less time brooding chicks than do
Arctic terns; consequently, Aleutian tern mortality rate is higher during the chick stage.
The eggs typically have an elongate ovate shape
and range from length. Their color ranges from a clay/olive green to a honey yellow,
they tend to be darker than eggs of other terns. Distinctive large and smaller black spots are irregularly marked over the egg.
After a three-week incubation period, the eggs hatch from early June until late July. Several days after hatching, young birds move to taller vegetation before moving with adults to staging areas along coast (
semiprecocial juvenils). After 4–5 weeks, the chicks start
fledging
Fledging is the stage in a flying animal's life between hatching or birth and becoming capable of flight.
This term is most frequently applied to birds, but is also used for bats. For altricial birds, those that spend more time in vulnerable c ...
.
Aleutian terns are easily disturbed from nests. As soon as an intrusion is detected, the adults fly off the nest. They are much slower at returning to nests after being disturbed than are
Arctic terns, taking up to 30 min to return.
It sometimes nests among
Arctic terns, which, like most white terns, are fiercely defensive of their nest and young and will attack large predators. The Aleutian tern, however, is not aggressive in defence of its nests or young.
Courtship
The
courtship display
A courtship display is a set of display behaviors in which an animal, usually a male, attempts to attract a mate; the mate exercises choice, so sexual selection acts on the display. These behaviors often include ritualized movement ("dances"), ...
of the Aleutian tern has never been thoroughly described, but all terns are thought to display the same strategies of courtship: ceremonial “fish flight,” “low flight,” “high flight,” and ground “parade”.
The Aleutian tern pre-courtship flights have been described in literature. Beginning on May, several terns participate in a synchronous ascending spiral flight, before the beginning of courtship in early June.
Pairs
Concentration, also known as Memory, Shinkei-suijaku (Japanese meaning "nervous breakdown"), Matching Pairs, Match Match, Match Up, Pelmanism, Pexeso or simply Pairs, is a card game in which all of the cards are laid face down on a surface and tw ...
do not always copulate at the colony; indeed, Mickelson et al. observed Aleutian terns that were courting on surrounding beaches of the Copper River Delta (Alaska), away from colonies.
Diet and Foraging
Aleutian terns primarily feed on small fish, but their diet also includes
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 ...
s,
insect
Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s and
zooplankton
Zooplankton are the animal component of the planktonic community ("zoo" comes from the Greek word for ''animal''). Plankton are aquatic organisms that are unable to swim effectively against currents, and consequently drift or are carried along by ...
. They
forage
Forage is a plant material (mainly plant leaves and stems) eaten by grazing livestock. Historically, the term ''forage'' has meant only plants eaten by the animals directly as pasture, crop residue, or immature cereal crops, but it is also used ...
mostly by flying, hovering low over water and swooping down or surface-dipping into the water to take their food from the surface.
Only contact- and surface-dipping have been observed, even in places where other species have been seen plunge-diving.
Indeed, terns are considered as poor swimmers because of their small webs and short legs.
Aleutian terns usually forage in shallow water, including tidal rips, along rivers, and over inshore marine waters. Occasionally adults and fledgling juveniles catch insects by hawking over freshwater ponds.
This species can forage in nearshore marine waters up to offshore from Seward Peninsula, and up to offshore from other colonies.
Individuals occasionally attempt to steal fish from other adults bringing fish to chicks.
Aleutian terns are skilled flyers and can take insects out of the air while flying.
Flight
Aleutian terns fly very gracefully; their flight is strong and undeviating, and their wing beats are slower than those of
Arctic
The Arctic ( or ) is a polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenland), Finland, Iceland, N ...
and
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 ...
s. They mostly fly above the ocean rather than above mainland.
Similarly to other terns species, the Aleutian tern walks relatively slowly because of its short legs.
Social behaviour
Aleutian terns are highly social. Usually, their
nest
A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...
s are settled within loose mixed-species colonies.
Monospecific colonies or isolated pairs are rare. Colony size usually ranges from 4–150 pairs, but up to 700 pairs on Sakhalin Island (Siberia). The Aleutian terns frequently nests with Arctic Terns in Alaska
and Common Terns in Siberia. It also happens that colonies of Mew Gull (''Larus canus'') are close to the Aleutian tern nests.
Less aggressive than Arctic terns; ''Onychoprion aleuticus'' is frequently chased at colonies and often excluded from mixed-species foraging areas by Arctic terns.
The latter can also jeopardize the Aleutian tern foraging activity by stealing its food.
Predators and parasites
Eggs and chicks of the Aleutian tern have been reported to be preyed on by the following list of predators:
*
Arctic fox
The Arctic fox (''Vulpes lagopus''), also known as the white fox, polar fox, or snow fox, is a small fox native to the Arctic regions of the Northern Hemisphere and common throughout the Arctic tundra biome. It is well adapted to living in ...
(''Vulpes lagopus'')
*
Coyote (''Canis latrans''),
Dog
The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...
s (''Canis familiaris''),
*
River otters (''Lutra canadensis''),
*
Weasel
Weasels are mammals of the genus ''Mustela'' of the family Mustelidae. The genus ''Mustela'' includes the least weasels, polecats, stoats, ferrets and European mink. Members of this genus are small, active predators, with long and slender b ...
s (''Mustela'' spp.),
*
Brown bear
The brown bear (''Ursus arctos'') is a large bear species found across Eurasia and North America. In North America, the populations of brown bears are called grizzly bears, while the subspecies that inhabits the Kodiak Islands of Alaska is ...
s (''Ursus arctos''),
*
Norway rats
The brown rat (''Rattus norvegicus''), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. One of the largest muroids, it is a brown o ...
(''Rattus norvegicus''),
*
Bald Eagles (''Haliaeetus leucocephalus''),
*
Parasitic Jaegers (''Stercorarius parasiticus''),
*
Glaucous-winged Gulls (''Larus glaucescens''),
*
Short-eared Owls (''Asio flammeus''),
*
Black-billed Magpies (''Pica pica''),
*
Northwestern Crows (''Corvus caurinus''),
*
Common Ravens (''Corvus corax)''
If Aleutian terns frequently fly high over the colony when disturbed by humans, they can nonetheless aggressively chase avian predators (but not as aggressively as
Arctic terns do). Some chicks may also be killed by
Arctic terns;
[https://www.fws.gov/r7/mbsp/mbm/seabirds/pdf/asis_complete.pdf U.S. Fish and Wildlife Service 2006] however, breeding success in the species is lower in the absence of Arctic terns as they often rely on their aggressivity to chase potential predators from the colony.
See also
*
Wildlife of Alaska
The wildlife of Alaska is both diverse and abundant. The Alaskan Peninsula provides an important habitat for fish, mammals, reptiles, and birds. At the top of the food chain are the bears. Alaska contains about 70% of the total North American br ...
References
External links
The North American Waterbird Conservation Plan
{{Taxonbar, from=Q793494
Onychoprion
Native birds of Alaska
Birds of the Aleutian Islands
Aleutian tern
Aleutian tern
Birds of North Asia