A medium-sized diving duck with a rounded head is the greater scaup (Aythya marila), just scaup in Europe or, colloquially, “bluebill” in North America. It breeds in Alaska, northern Canada, Siberia, and the northernmost reaches of Europe during the summer months. It migrates south to the coasts of North America, Europe, and Japan throughout the winter. There is also a larger, more oval, green-tinted head in male scaup than male lesser scaup. A shiny black head, tinted green, has a male greater scaup. Glossy black is the collar, breast, and upper mantle, and white is the flanks and the belly, often with gray vermiculations on the lower flanks. With fine black vermiculations, the back is whitish, and black is the tail and upper- and under-tail coverts. The wing has a broad white speculum covering almost all of the main and secondary spans. With a black nail, the bill is a light blue-grey, the legs and feet are gray and the iris is gold. With a 71-84 cm (28-33 in) wingspan and a body mass of 726-1,360 g (1,601-2,998 lb), the adult greater scaup is 39-56 cm (15-22 in) long. The adult female, with white wing markings similar to those of the male but slightly duller, has a brown body and head. At the base of the bill, it has a white band and brown oval-shaped patches that are a much duller shade of blue than that of the drake. Similar to adult women, juvenile greater scaup appears similar. A mottled brown-and-gray body and a blackish head: Non-breeding males look like a cross between a female and a breeding male.
To feed on aquatic plants and animals, Greater Scaup dive. The main diet items are mollusks in coastal areas. Seeds, leaves, stems, roots, and tubers of aquatic plants (sedges, pondweeds, musk grass, wild celery), etc are important things in freshwater ecosystems. Greater Scaup forms big flocks on bays, streams, and larger wetlands during migration and winter. With each other, they prefer to form tight groups and often mix with other diving ducks. At the age of two, they start breeding but begin constructing nests in the first year. On the return migration to the summer breeding grounds, the drakes have a complex courtship that ends with the formation of monogamous pairs. Females lay six to nine olive-buff-colored eggs in a clutch. Within 24 to 28 days, the eggs hatch. Since they are difficult to differentiate during aerial surveys, greater and lower scaup are counted together. Greater Scaup is projected to constitute about 11 percent of the population of continental scaup. Greater Scaupes are also entangled in fishing nets, so every year large numbers of them drown in nets. Greater Scaup will catch avian influenza, so the potential for future outbreaks to threaten higher populations of scaup. Since the 1980s, the population of Scaup has gradually decreased. The key factors leading to the decline are thought to be pollutants, lower female survival, and decreased recruitment due to changes in breeding habitat or food resources. In North America and Europe, the Greater Scaup is a common game bird. They are hunted for both sport and commercial purposes in Denmark, Germany, Greece, France, the United Kingdom, and Ireland, and Iran.