The Greater and Lesser Scaups are somewhat hard to distinguish. The greater is about 18" long and the lesser is 17.5". The Greater Scaup has a greenish cast in the black feathers whereas the Lesser has a purplish cast. The Greater's head is a little more round. Both varieties are found in our area (Vancouver, Canada) but the Greater is more common here than the Lesser.
This is a manipulated image. The whole image has been converted to black and white except the beak, eye and a small patch under the eye. The reduction of the colour brings out the texture in the feathers - although this is far more noticable in a large print than in the images made for the web.