The White-winged Scoter nests on freshwater lakes and wetlands in boreal forest, primarily in the northwestern interior of North America, and overwinters along the coasts of the Pacific and Atlantic oceans. This species has a large stocky body and a prominent white speculum on each wing. Males are distinguished by their black plumage and a hump in the middle of their brightly marked bill, and in both sexes the base of the bill is swollen.
When taking off, the White-winged Scoter runs and flies along the surface of the water for a short distance. Once in the air, its flight is swift and direct, powered by a rapid wing beat. Individuals often fly low over the water in lines referred to as strings, but most of their time is spent loafing or swimming on the surface. They feed almost exclusively by diving, generally taking prey on or near the bottom. Mollusks (especially the Blue Mussel, Mytilis edulis) and crustaceans are important foods on wintering areas—generally open coastal environments, especially bays and inlets, where food is likely to be most abundant. On its breeding areas, this species favors large wetlands and lakes, either brackish or freshwater sites. Foods on breeding areas include crustaceans (especially the amphipod Hyalella azteca) and insect larvae distributed along or near the bottom.
The White-winged Scoter is serially monogamous—the male leaves his mate soon after she begins laying eggs. Females sometimes nest in high densities on islands, but more often appear to nest up to several kilometers from water. Nests are typically hidden beneath dense, thorny vegetation, such as gooseberry (Ribes spp.) or rose (Rosa spp.) bushes. Individuals return to the same general area to nest in subsequent years and may even use the same nest bowl. The survival rate of young White-winged Scoter is low, with most mortality occurring in the first few weeks of life.
Although not generally prized by sport hunters, significant numbers are shot each year, especially along the Atlantic Coast of North America where there is a tradition of hunting sea ducks. Because of this species' low rate of recruitment and strong philopatry to nesting areas, disturbance during the nesting season and hunting on breeding areas have the potential to impact local populations. The population status of the White-winged Scoter is poorly known due to remoteness of boreal breeding areas and because some waterfowl surveys pool data for the 3 North American scoter species. See Demography and Populations: Population Status.