Aleutian Tern
[order] CHARADRIIFORMES | [family] Laridae | [latin] Onychoprion aleuticus | [UK] Aleutian Tern | [FR] Sterne des Aleoutiennes | [DE] Aleuten-Seeschwalbe | [ES] Charrn Aleutiano | [NL] Aleoetenstern
Subspecies
Monotypic species
Physical charateristics
Measuring 30-32 cm long with a 73-75 cmd wingspan, the Aleutian Tern weighs only 3.9 ounces. In breeding plumage, this fairly small seabird is grey over most of its body with a white tail and underwing. Contrasting with the white forehead and face, the black cap and bill connect through a thick line passing through the black eye. The short legs are also black. In nonbreeding plumage, the Aleutian Tern is grey above and white below. Its black cap withdraws to cover the back of the head and the nape and to just touch the back of the eye with a thin, black strip. In flight, this tern appears deep chested and flies directly, with deep wing beats.
Listen to the sound of Aleutian Tern
[audio:http://www.aviflevoland.nl/sounddb/A/Aleutian Tern.mp3]
Copyright remark: Most sounds derived from xeno-canto
| wingspan min.: | 73 | cm | wingspan max.: | 75 | cm |
| size min.: | 30 | cm | size max.: | 32 | cm |
| incubation min.: | 21 | days | incubation max.: | 23 | days |
| fledging min.: | 29 | days | fledging max.: | 23 | days |
| broods: | 1 | eggs min.: | 2 | ||
| eggs max.: | 3 |
Range
Eurasia, North America : North Pacific coasts
Habitat
During the breeding season and perhaps for migratory staging, the Aleutian Tern lives over coastal waters. Here, it forages over shallow, oceanic waters, estuaries, rivers, and freshwater ponds. Breeding colonies require remote locations with even terrain: islands, tundra, arctic and subarctic meadows, river deltas, and sandy spits. A variety of vegetation may provide some concealment for nests: grasses, sedges, deep moss, low shrubs, and rushes. The nonbreeding habitat is probably the open ocean.
Reproduction
Nesting occurs in a variety of habitats (e.g. islands, shrub-tundra, grass or sedge meadows, and freshwater and coastal marshes). The nest is generally a depression in short or matted vegetation and nests are widely scattered in the colony. Courtship displays have rarely been observed, but all terns are known to engage in ritualized flights, feeding, and walking. In loose colonies near the coast, regularly mixed with other tern species like the Arctic Tern, the Aleutian Tern makes a simple bowl nest by depressing grasses, sedge, sand, or even fine gravel. The nest is sometimes lined with grass stems. Both sexes have brood patches and probably take turns incubating 1-3 light yellow eggs, marked with dark brown speckles and blotches. In about 3 weeks, the downy hatchlings emerge capable of leaving the nest, if necessary. Two weeks after hatching, the young hide in nearby vegetation and fledge at 1 month old. The parents continue to feed them through the fall, when juveniles gather before migration.
Feeding habits
Small fish, crustaceans, and insects are the preferred foods for Least Terns; small mollusks and marine worms are eaten as well. Least Terns forage over water, hovering briefly before plunging in to catch tiny prey just below the surface; they sometimes dip to pluck prey from the surface or to catch insects in flight.
Conservation
This species has a large range, with an estimated global breeding Extent of Occurrence of 50,000-100,000 km2. It has a large global population estimated to be 30,000-35,000 individuals (Wetlands International 2002). Global population trends have not been quantified, but the species is not believed to approach the thresholds for the population decline criterion of the IUCN Red List (i.e. declining more than 30% in ten years or three generations). For these reasons, the species is evaluated as Least Concern.
In North America, this tern breeds only in Alaska from the Kasegaluk Lagoon along the northwest coast to Glacier Bay on Alaska’s southern coast. Colonies are not faithful to one coastal site but are found most often from Point Hope south around the Seward Peninsula and into the Yukon-Kuskokwim River Delta, Cape Newenham, the Alaska Peninsula, and predator- free Aleutian Islands. Colonies are also scattered at several sites along the Siberian coast. The winter range and migratory routes are unknown. Observations in the 1990’s suggest that it winters and/or migrates near the coasts of Hong Kong, Singapore, and several Indonesian Islands (Karimun, Bintan, Java, Bali and Sulawesi).
In North America, this tern breeds only in Alaska from the Kasegaluk Lagoon along the northwest coast to Glacier Bay on Alaska’s southern coast. Colonies are not faithful to one coastal site but are found most often from Point Hope south around the Seward Peninsula and into the Yukon-Kuskokwim River Delta, Cape Newenham, the Alaska Peninsula, and predator- free Aleutian Islands. Colonies are also scattered at several sites along the Siberian coast. The winter range and migratory routes are unknown. Observations in the 1990’s suggest that it winters and/or migrates near the coasts of Hong Kong, Singapore, and several Indonesian Islands (Karimun, Bintan, Java, Bali and Sulawesi).
Migration
Little information. Arrives in breeding areas mid-May and leaves by mid-Sept. Non-breeders presumably pelagic, dispersing into Bering Sea and N Pacific. No Neartic records outside Alaska, and only accidental in Commander Is and Japan. Winter records from Philippines, and recorded as migrant Hong Kong, but main wintering areas still unknown. One extraordinary record of vagrancy: an adult in Britain in May 1979.
Distribution map
