The Collaborative International Dictionary of English v.0.48:
Scaup \Scaup\ (sk[add]p), n. [See Scalp a bed of oysters or
1. A bed or stratum of shellfish; scalp. [Scot.]
2. (Zool.) A scaup duck. See below.
Scaup duck (Zool.), any one of several species of northern
ducks of the genus Aythya, or Fuligula. The adult
males are, in large part, black. The three North American
species are: the greater scaup duck (Aythya marila, var.
nearctica), called also broadbill, bluebill,
blackhead, flock duck, flocking fowl, and raft
duck; the lesser scaup duck (Aythya affinis), called
also little bluebill, river broadbill, and shuffler;
the tufted, or ring-necked, scaup duck (Aythya
collaris), called also black jack, ringneck,
ringbill, ringbill shuffler, etc. See Illust. of
Ring-necked duck, under Ring-necked. The common
European scaup, or mussel, duck (Aythya marila), closely
resembles the American variety.