A small dark duck measuring 14–20 inches (36–51 cm). Male is blue-gray (appearing black at a distance), with chestnut flanks and distinctive white patches on head and body. Female is dusky brown with two or three whitish patches on sides of face. In flight, this species lacks large white patches on wings.
Swift-moving streams in summer; rocky, wave-lashed coasts and jetties in winter.
Six to eight pale buff or cream-coloured eggs in a mass of down concealed in a crevice in rocks along a stream.
Breeds from Alaska and Yukon south to Wyoming and Sierra Nevada of California, and from southern Baffin Island south to Labrador and Gaspe Peninsula. Winters along coasts south to central California and Long Island. Also in Eurasia.
A mouse-like squeak and various low whistles.
During breeding season, the harlequin duck is a bird of swift mountain streams, where it catches the nymphs of stoneflies, caddisflies, and other aquatic insects. In the fall, the birds move to the coast, the preferred habitat where they thrive in rough water of a different kind, riding the surf in toward rocky cliffs, and wrenching mussels, chitons, barnacles, and other attached animals from the surface and diving for crabs and other crustaceans.