Aleutian Tern

The Aleutian tern (Onychoprion aleuticus), a medium-sized seabird, graces the subarctic skies with its presence. It measures 32–39 cm in length, with a wingspan of 75–80 cm, and tips the scales at a modest 84–140 g. This tern is characterized by its short pointed bill and a long, deeply forked tail, which it carries with elegance as it soars above the ocean.

Identification Tips

During the breeding season, the adult Aleutian tern can be identified by its striking white forehead, contrasting with a black cap. Its mantle is a mid-grey, and the underparts are darkish grey, while the rump and tail are white. The underwing is predominantly whitish, with dark-tipped primaries and a distinctive dark bar on the secondaries. The bill and legs of this tern are black, a feature that distinguishes it from the bright red extremities of the Arctic tern during the same period.

Habitat

The Aleutian tern is a pelagic bird when not breeding, favoring partially vegetated sandy beaches, grassy meadows, mossy boglands, and marshes. It is often found on isolated rocky islands or along coasts, particularly near river mouths.

Distribution

This migratory bird breeds along the Pacific coastlines of Alaska and Russia, with colonies scattered from the Chukchi Sea to the Gulf of Alaska. In winter, it travels to tropical waters near the Equator in the western Pacific, with sightings reported from Hong Kong to Indonesia and as far as Australia's eastern coast.

Behaviour

Aleutian terns are colonial breeders and exhibit site fidelity. They are known for their graceful flight, strong and undeviating, with slower wing beats than their Arctic and Common tern counterparts. On land, their movement is somewhat slower due to their short legs.

Song & Calls

The Aleutian tern's vocal repertoire includes a high-pitched, soft, rolling whistle, with a distinctive "chif-chif-chu-ak" call that is less harsh than that of the Arctic tern. Another call is a prolonged "whee-hee-hee-hee," stressed on the first syllable. They are generally silent while incubating.

Breeding

Breeding pairs form shortly after arrival at the breeding grounds, with nest construction occurring in late May to early June. The typical clutch size is two eggs, which are incubated by both parents. The eggs are elongate ovate, ranging in color from clay/olive green to honey yellow, with distinctive black spots. Chicks are semi-precocial and start fledging after 4–5 weeks.

Similar Species

The Aleutian tern is often confused with the Arctic tern, especially outside the breeding season when plumage differences are less pronounced. However, the white forehead and black bill and legs during the breeding season are key identifiers.

Diet and Feeding

The diet of the Aleutian tern consists mainly of small fish, crustaceans, insects, and zooplankton. They forage by flying low over water and dipping to the surface to catch prey, rarely engaging in plunge-diving due to their poor swimming ability.

Conservation status

The Aleutian tern is currently listed as "Vulnerable" due to rapid declines in population over generations. Threats include habitat modification, predation, egg harvesting, human disturbance, and ecological stresses in their wintering areas. Conservation efforts are underway, including research to understand the causes of decline and to develop effective management strategies.