Fairly small, boldly patterned diving duck that lives a seemingly dangerous life near fast-moving water and jagged rocks. Male is striking and unmistakable. Female is dark brown with small white patches on face; compare with female scoters but note smaller size and smaller bill of Harlequin. In summer, almost invariably seen in pairs on rocky streams where they breed. Gathers in small flocks on rocky coastlines in winter. Feeds on insects, fish, and aquatic invertebrates. Frequently dives underwater. Vocalizations are cute, high-pitched squeaks. In North America, more numerous in the west than in the east; also occurs in eastern Asia and Iceland.