What is "ringbill shuffler"

Scaup \Scaup\ (sk[add]p), n. [See Scalp a bed of oysters or mussels.]

1. A bed or stratum of shellfish; scalp. [Scot.]

2. (Zo["o]l.) A scaup duck. See below.

   Scaup duck (Zo["o]l.), 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 ( A. affinis), called also little bluebill, river broadbill, and shuffler; the tufted, or ring-necked, scaup duck ( A. 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 ( A. marila), closely resembles the American variety.