Adults have white underparts, though the rest of the plumage goes through a complex moulting process. The male has a long pointed tail and a dark grey bill crossed by a pink band. In winter, the male has a dark cheek patch on a white head and neck, a dark breast and white body. In summer, the male is dark on the head, neck and back with a white cheek patch. The female has a brown back and a relatively short pointed tail. In winter, the female's head and neck are white with a dark crown. In summer, the head is dark. Juveniles resemble adult females in autumn plumage, though with a lighter, less distinct cheek patch.
Habitat and Distribution
Their breeding habitat is in tundra pools and marshes, but also along sea coasts and in large mountain lakes in the North Atlantic region, Alaska, northern Canada, northern Europe and Russia. They are migratory and winter along the eastern and western coasts of North America, on the Great Lakes, coastal northern Europe and Asia, with stragglers to the Black Sea. The most important wintering area is the Baltic Sea, and about 4.5 million birds gather.
They feed by diving for mollusks, crustaceans and some small fish. Although they usually feed close to the surface, they are capable of diving to depths of 60 m.
The nest is located on the ground near water; it is built using vegetation and lined with down.
Calls and Songs
The males are vocal and have a musical yodelling call ow, ow, owal-ow.