UKBirds

Greater Scaup

Aythya marila

The Greater Scaup, just Scaup in Europe, or colloquially "Bluebill" in North America for its bright blue bill, is a mid-sized diving duck though it is larger than the closely related Lesser Scaup. It is a circumpolar species, which means that its range circles one of Earth's poles. It spends the summer months breeding in Alaska, northern Canada, Siberia, and the northernmost reaches of Europe. During the winter, it migrates south down the coasts of North America, Europe, and Japan.

Drake Greater Scaup are larger and have more rounded heads than females; they have a bright blue bill and yellow eyes. They have dark heads with a glossy green tint, white undersides and wings with white on the tips. The females are mostly brown, with white bands located on their wingtips. They have a blue bill that is slightly duller then the drake's.

Greater Scaup nest near water, typically on islands in northern lakes or on floating mats of vegetation. They begin breeding at age two, but start building nests in the first year. The drakes have a complex courtship procedure, which takes place on the return migration to the summer breeding grounds and concludes with the formation of monogamous pairs. Females lay a clutch of six to nine olive-buff colored eggs. The eggs hatch in 24 to 28 days. The down-covered ducklings are able to follow their mother in her search for food immediately after hatching.

Greater Scaup eat aquatic mollusks, plants, and insects, which they obtain by diving underwater. They form large groups, called "rafts", that can number in the thousands. Their main threat is human development, although they are preyed upon by owls, skunks, raccoons, foxes, coyotes, and humans. Greater Scaup populations have been declining since the 1980s; however, they are still listed as a species of least concern on the IUCN Red List.

The adult Greater Scaup is 39-56 cm (15-22 in) long with a 71-84 cm (28-33 in) wingspan and a body mass of 726-1,360 g (1.60-3.0 lb). It has a blue bill and yellow eyes and is 20% heavier and 10% longer than the closely related Lesser Scaup. The male has a dark head with a green sheen, a black breast, a light back, a black tail, and a white underside. The drake or male Greater Scaup is larger and has a more rounded head than the female. The drake's belly and flanks are a bright white. Its neck, upper chest, and tail feathers are a glossy black, while its lower flanks are gray. The drake also has a white speculum on its wings. The adult female has a white band and brown oval shaped patches at the base of the bill, which is a slightly duller shade of blue than the drake's bill. Females have grey on both their legs and feet. They have a brown body and head, with white bands on their wingtips. Juvenile Greater Scaup look similar to adult females. The Greater Scaup drake's eclipse plumage looks similar to its breeding plumage, except the pale parts of the plumage are a buffy gray. Distinguishing Greater from Lesser scaups can be extraordinarily difficult in the field, especially in terms of plumage, although (depending on posture) their general shape is slightly different.