The Lesser Scaup (Aythya affinis) is a small diving duck; smaller than the Greater Scaup.
Adults have a blue bill and yellow eyes. Adult males have a dark head with a purple sheen, a black breast, a light back, a black tail and a white bottom. Adult females have a white band at the base of the bill and a brown head and body.
They breed in marsh ponds throughout Alaska and western Canada. They nest in a sheltered location on the ground near water.
They migrate in flocks and winter in lakes, rivers and sheltered coastal waters along the west coast of North America, the southern United States and northern South America. They are more likely to be found on freshwater than Greater Scaup. These birds move south late in the fall and return in early spring.
They are a rare but apparently increasing vagrant to Western Europe.
These birds dive and swim underwater, occasionally dabbling. They mainly eat mollusks and aquatic plants. It has been reported that this bird and the Greater Scaup have shifted their traditional migration routes to take advantage of the presence of Zebra mussels in Lake Erie. This may pose a risk to these birds because zebra mussels are efficient filter feeders and so accumulate environmental contaminants rapidly.