Guide to North American Birds

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Photo: Arthur Morris/Vireo

Aleutian Tern

Onychoprion aleuticus

An uncommon bird, nesting around the Bering Sea and nearby waters, including much of the southern Alaskan coast and Aleutian Islands. May associate with Arctic Tern, but is far less numerous. Its habits have not been thoroughly studied. Its winter range was completely unknown until the late 1980s; now it is known that many Aleutian Terns spend the winter near the Equator in the western Pacific.

Conservation status	Uncommon and local, colonies vulnerable to disturbance. No obvious trends in population.
Family	Gulls and Terns
Habitat	Northern coasts (summer); open ocean (winter). During most of year apparently at sea, moving south to tropics in winter, although details poorly known. In breeding season along northern coastlines, foraging mostly offshore, nesting on open islands, sandbars, or beaches with dense low ground cover.

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Feeding Behavior

Forages mostly by flying or hovering low over water, dipping down to take items from surface; apparently seldom plunge-dives into water.

Eggs

1-2, sometimes 3. Buff to olive, heavily marked with dark brown. Incubation is probably by both sexes, about 22-23 days. Young: Both parents probably bring food for young. Age at first flight about 25-31 days. Young may remain around colony one or two weeks after fledging; age at independence unknown.

Young

Both parents probably bring food for young. Age at first flight about 25-31 days. Young may remain around colony one or two weeks after fledging; age at independence unknown.

Diet

Includes crustaceans, fish, insects. Diet in summer includes many euphausiid shrimp and other crustaceans, small fish, and insects. Winter diet essentially unknown.

Nesting

Usually nests in small colonies, often associated with Arctic Terns. Unlike most terns, parents do little or nothing to defend nest against predators or intruders, simply departing at approach of danger. May benefit by nesting with Arctic Terns, which are more aggressive in defense of colony. Nest site is close to water on low sandspit, island, or beach, among grasses or other vegetation. Nest is inconspicuous, a shallow depression in moss, matted grass, low vegetation.

Illustration © David Allen Sibley.
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Text © Kenn Kaufman, adapted from
Lives of North American Birds

Migration

Winter range still poorly known, was completely unknown until late 1980s; most apparently winter at sea near the Philippines or Indonesia. Arrives on Alaska breeding grounds in May, departs mostly in August. One seriously lost individual once was found in Britain.