Black-throated Loon

The black-throated loon (Gavia arctica), also known as the Arctic loon or black-throated diver, is a migratory aquatic bird of the northern hemisphere. It is characterized by its striking breeding plumage, with a grey head and hindneck, a prominent black throat with a soft purple gloss, and black upperparts adorned with white squares on the mantle and scapulars. The underparts are predominantly white. This species exhibits sexual monomorphism, meaning males and females are similar in appearance.

Identification Tips

In breeding plumage, the adult black-throated loon can be identified by its black throat and foreneck, grey head, and white-striped sides. The juvenile resembles the non-breeding adult but is more brown overall with a buffy scaling on the upperparts. The flanks are white, which distinguishes it from the similar Pacific loon.

Habitat

During the breeding season, the black-throated loon favors isolated, deep freshwater lakes in northern Europe and Asia. In the non-breeding season, it migrates southward to ice-free sea coasts, often found in inshore waters along sheltered coasts.

Distribution

The black-throated loon breeds across northern Europe and Asia, with wintering grounds along the north-east Atlantic Ocean and the eastern and western Pacific Ocean coasts.

Behaviour

This loon is adept at taking off from water surfaces by pattering along a "runway" and is known for its barking "kwow" flight call. It nests on the ground or on emergent vegetation near lakes, with a tendency to reuse nest sites.

Song & Calls

The male's breeding song is a loud, rhythmic whistling, accompanied by a "áááh-oo" wail and a growling "knarr-knor" at night. An alarm call of a rising "uweek" can be heard at the nest.

Breeding

The black-throated loon starts breeding in April in the southern part of its range, delaying until after the spring thaw in the north. It constructs an oval-shaped nest near the lake, laying a clutch of two brown-green eggs, which are incubated for 27 to 29 days. Chicks are mobile upon hatching and are fed by both parents.

Diet and Feeding

As a top predator in some subarctic lakes, the black-throated loon feeds on fish, insects, molluscs, crustaceans, and occasionally plant matter. It forages alone or in pairs, diving no deeper than 5 meters, with most dives resulting in successful prey capture.

Conservation status

The black-throated loon is currently listed as Least Concern by the IUCN, despite a declining population. It is protected under the Migratory Bird Treaty Act of 1918 and the Agreement on the Conservation of African-Eurasian Migratory Waterbirds.

Similar Species

The Pacific loon is similar but lacks the white flanks seen in the black-throated loon.

Predators and parasites

The black-throated loon is vulnerable to predation by mammals such as red foxes and avian predators like hooded crows. It can also be parasitized by nematodes like Eustrongylides tubifex.

Threats

Threats to the black-throated loon include acidification and heavy-metal pollution of breeding lakes, oil pollution, fishing nets, and sensitivity to coastal wind farms. The adult mortality rate is estimated at 10% annually.