The name of the greater scaup (Aythya marila) – just scaup in Europe or, colloquially, "bluebill" in North America – is thought to be derived from its habit of feeding on broken shells, called scaup. Alternatively, the name may come from its display call of "scaup scaup". Its diet chiefly consists of mollusks, especially mussels; it also eats crustaceans such as crabs, and various insects and worms. Unlike its look-alike relative the Lesser Scaup, the Greater Scaup is found across Eurasia as well as North America. 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. The nest of a Greater Scaup is usually lined with a thick layer of down plucked by the mother from her own breast.