Posted by David Fix (206.13.45.107) on December 17, 2001 at 17:05:21:
I believe both scaup in the upper image are Greater Scaup. Each bird has a heavy-based bill and the highest point of the crown is slightly forward of the eye-- as if a golf ball were imbedded in the front of the skull. The female has an extensive pale swath on the rear of the face, a mark seldom if ever shown by female Lesser Scaup. The bottom bird is clearly a male Lesser Scaup, identified by the head shape, with the highest point of the crown behind the eye and with the characteristic crown shape shown by each sex of this species.