The Greater Scaup is a holarctic breeding diving duck that winters along the North American coasts in large numbers.  Breeding throughout much of the boreal and arctic regions of the world, Greater Scaup barely touch the northern rim of the Neotropics in winter when small numbers winter along the Pacific Coast to Baja California, Mexico .  Males are black on the rear end, head, and neck with a grizzled gray back, while females are largely brown with white at the base of the bill.  Though often rather difficult to separate from Lesser Scaup in the field, Greater Scaup can be identified by large size, a high forehead, rounded crown, broad bill, and white extending through the secondaries and into the inner primaries as shown in flight.  Though there are many exceptions, Greater Scaup are more likely to be found in large groups on saltwater in winter while Lessers tend to prefer freshwater.