Fairly small, boldly patterned diving duck that lives a seemingly dangerous life near fast-moving water and jagged rocks. Females dull brown with small white patches on face; compare with female scoters but note smaller size and smaller bill of Harlequin. In summer, they are almost invariably seen in pairs on rocky streams where they breed. They gather in small flocks on rocky coastlines in winter. Feeds on insects, fish, and aquatic invertebrates. Frequently dives underwater. Vocalizations are cute, high-pitched squeaks. Western population is more numerous than Atlantic population.