The Scaup-Ducks, of which some six or eight forms are recognized, are by some placed in the same genus with those last mentioned, and by others in a separate genus (Fuligula). In these birds the culmen is as long as the outer toe with its claw, the bill is wider at the tip than at the base, and the head and neck in the adult males is black, while the speculum is white or bluish gray tipped with black. Perhaps the best-known species is the Scaup-Duck (F. Manila), a bird from eighteen to twenty inches long, found from western Europe to Kamchatka and throughout North America. It breeds in the extreme northern parts of its range, penetrating to lakes and rivers often at a considerable distance from the sea. It is more or less gregarious at all seasons, and feeds on shell-fish, crustaceans, and aquatic plants. Its voice is described as very harsh and discordant, resembling the word scaup, screamed in a loud tone. The nest is placed near water and the eggs are from six to nine in number, of a pale greenish gray color. It is found over North America generally, breeding in the far North, Dail having found it nesting near the mouth of the Yukon, making but a rude excavation on the ground and lining it with a few straws.. MacFarlane did not find it in Arctic America, although it probably nests there, nor did Mr. Bent find it in North Dakota, although it is reported as nesting occasionally in Minnesota and Manitoba. In winter it comes far south, being abundant along the California coast, and on the Atlantic coast from Long Island to northern South America, preferring the salt-water marshes. The Lesser Scaup-Duck (F. Affinis), also of North America, is smaller than the last and has the head in the male glossed with purple instead of green. Its habits are similar to those of its larger relative, and, although its main nesting ground is in the far North, it not infrequently nests from Iowa and Manitoba northward. It, however, has a greater preference for fresh water and was observed by Mr. Bent about the larger lakes in North Dakota, where he found several nests. These were usually on islands and were concealed in the taller prairie grass or under low bushes. The eggs number from nine to fifteen and are of a rich dark buff or coffee-color. It appears that the males desert the females after incubation begins and flock by themselves in the sloughs or small ponds.
Other forms are the Chinese Scaup-Duck F. Affinis Mariloides) of eastern Asia, the New Zealand Scaup (F. novce-zealandice), the Ring-necked Duck (F. Collaris) of North America, which takes its name from the presence of a chestnut collar about the neck, and finally the Crested Scaup-Duck (F. Fuligula) of the eastern part of the Old World, which may be known by the long, pendent occipital crest. Several fossil forms have also been described from the upper Tertiary of France and Italy.