Any of three species (genus Aythya, family Anatidae) of diving ducks. The greater scaup, or big bluebill (A. marila), breeds across Eurasia and most of the Nearctic region. The lesser scaup, or little bluebill (A. affinis), breeds in northwestern North America. Both are popular game birds, 15–20 in. (38–51 cm) long, that winter along the U.S. coasts. Males have a dark breast and grayish back but differ in head colour and wing markings; females are brown with white patches around the blue bill. Scaups eat mainly clams. The third species is the New Zealand scaup (A. novaeseelandiae).