The black scoter is a medium-sized sea duck approximately 43–49 cm (17–19 in) long. Males are slightly larger than females and weigh 980– 1100 grams (2.2–2.4 lb). Males are solid black and have a yellow knob on their relatively small bill, whereas females are dark brown with a pale cheek patch and a dark crown. They retain the same plumage year-round. In flight, the undersides of their wings flash silvery gray in contrast to their dark bodies. Their wings make a whistling noise in flight. Males are very vocal and make a continuous mellow, plaintive whistling sound. Females make a low growling sound during courtship.