The greater scaup (Aythya marila) name may come from "scalp", a Scottish and Northern English word for a shellfish bed or from the duck's mating call: "scaup scaup". Known as scaup in Europe or, colloquially, "bluebill" in North America, it is a mid-sized diving duck, larger than the closely related lesser scaup. The species name marila is from the Greek word for charcoal embers or coal dust. The birds in North America are considered a separate subspecies. They look remarkably similar to the Lesser Scaup, with only slight differences in head shape: the Greater Scaup has a rounded head, the Lesser Scaup a peaked head. The only circumpolar diving duck, the Greater Scaup breeds across the tundra regions in North America and Europe. They congregate by the hundreds and thousands along the Pacific and Atlantic coasts during winter.