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 ).