Onychoprion aleuticus (S.F.Baird, 1869)

Taxonomy and Physical Description

The Aleutian tern (scientific name Onychoprion aleuticus (S.F.Baird, 1869)) is a medium-sized tern, measuring 32–39 cm (13–15 in) in length, with a 75–80 cm (30–31 in) wingspan, and weighing 84–140 g (2.9–5.0 oz). It has a short pointed bill and a long, deeply forked tail.

Breeding Colony Locations

During breeding season, colonies of Aleutian terns gather along Pacific coastlines of Alaska and Russia. Confirmed breeding colony locations include the coast of the Chukchi Sea (western Alaska), the Seward Peninsula, the Yukon-Kuskokwim River Delta along the Alaska Peninsula, the Aleutian Islands, the Kodiak Archipelago, the Kenai Peninsula, the Copper River delta, and along the Gulf of Alaska.

Breeding Population Estimates

The current estimated worldwide minimum breeding population is 31 000 birds. Most colonies are located in the Siberian region of Russia, with 25 602 birds across 89 colonies, while the remaining 18% of the population (5 529 birds across 111 colonies) occurs in Alaska.

Regional Population Trends

Within the last decade, colony declines and disappearances at individual sites in Alaska have been reported.

Migratory Status

This species is strongly migratory. While its wintering range is not well understood, it is believed to be located off the coasts of Indonesia and Malaysia.

Wintering Sighting Records

Small flocks of Aleutian terns have been increasingly sighted in coastal areas around Hong Kong during spring and fall, around Singapore and Indonesia between October and April, and in the coastal waters of Java, Bali and Sulawesi during December.

Migration Route Indicators

The regular appearance of Aleutian terns off Hong Kong in fall indicates one possible route for southbound migration. This tern differs from closely related species as it is the only one that migrates annually between a subarctic breeding zone and tropical wintering areas in the South Pacific.

Unusual Migratory Context

Only a very small number of Charadriiformes that breed in Alaska have a connection to East Asia. In December 2017, Aleutian terns were spotted for the first time on Australia's eastern coast.

Breeding Habitat Preferences

Aleutian terns typically inhabit partially vegetated sandy beaches, grassy meadows, mossy boglands and marshes. These habitats are found either on isolated rocky islands or along coasts, often near river mouths.

Non-Breeding Habitat

When not breeding, the Aleutian tern is pelagic.