Fairly common sea duck; feeds by diving. Breeds on tundra lakes; winters at sea in coastal bays, estuaries, harbors. Rarely seen inland on fresh water, mainly during migration periods. Occurs locally in flocks of hundreds, but also found as singles and small groups. Male distinctive: wholly black with raised knob at base of bill, yellow wedge on top of bill. Female dark brown overall with pale cheeks. In flight looks all-dark, often flying in rather tight groups low to fairly high over the sea.