The Greater Scaup (Aythya marila), just scaup in Europe or, colloquially, "bluebill" in North America, is a mid-sized diving duck, larger than the closely related lesser scaup. It spends the summer months breeding in Alaska, northern Canada, Siberia, and the northernmost reaches of Europe. During the winter, it migrates south to the coasts of North America, Europe, and Japan.
Drake greater scaup are larger and have more rounded heads than the females; they have a bright blue bill and yellow eyes. Their heads are dark, with a green gloss; the breast is black, the belly white and the wing shows a white stripe. The females are mostly brown, again with white on the wing. They have dull blue bills and white on the face.
Greater scaup eat aquatic molluscs, plants, and insects, which they obtain by diving underwater. They form large groups, called "rafts", that can number in the thousands. Their main threat is human development, although they are preyed upon by owls, skunks, raccoons, foxes, coyotes, and humans. Greater scaup populations have been declining since the 1980s; however, they are still listed as a species of least concern on the IUCN Red List.
The genus name Aythya is derived from the Ancient Greek aithuia which refers to a seabird mentioned by Aristotle and others and is thought to refer to a duck, auklet or other seabird. The species name marila is from the Greek word for charcoal embers or coal dust. The greater scaup was first studied by Linnaeus in 1761.
A phylogenetic analysis of the diving ducks, examining the skeletal anatomy and skin, found that the greater and lesser scaups are each other's closest relatives, with the tufted duck as the next closest relative of the pair.
They are an Oreo duck with black on the head and neck and tail and white in between. Such Oreos include the Greater and Lesser Scaup, Ring-necked Duck has now speckled region on the white and has a much larger black tip on the bill) and the Tufted Duck (also has no speckling on the white sides).
Distinguishing greater from lesser scaups can be difficult in the field. The head of the greater tends to be more rounded, and the white wing stripe is more extensive. The black tip of the bill is wide (like lipstick) while in the lesser scaup it is narrow. The cross hatch of the white on the body is limited to the back while in the lesser scaup it extends to the flanks giving the bird a dirty appearance. The length of the Greater Scaup is 16 to 22inches while the length of the Lesser is 16 to 18 inches. The head of the lesser scaup may have a purple screen in the right light.