Since I have been belaboring the look-alike goldeneyes in recent posts, I will continue the theme for one more day with the lesser scaup (Aythya affinis) and its “twin” the greater scaup (Aythya marila).
A comment in “Complete Birds of North America” edited by Jonathan Alderfer states, “field marks for scaup are subtle aspects of structure that can be altered by a bird’s behavior and posture”. For example, size: the greater scaup is “noticeably larger”. And if there is only one specimen around? The greater scaup has a more rounded head and the lesser’s head is more angular. The lesser has a small bill with parallel sides while the greater’s bill is longer and expands slightly toward the tip. “Subtle” is right – at least for my level of expertise.
The plumage does little more to clarify the situation. Both species have a black head, but the greater’s head has a green sheen while the gloss on the lesser’s head is purple, of course, the head of the lesser can often appear green. I agree with the guide when it says, ” scaup are truly difficult and can cause much frustration”.
Range and habitat can provide a little clue to identity, but is certainly not a guarantee. The greater scaup is more a bird of coastal bays and inlets preferring deeper water, while the lesser scaup is more common in fresher, shallower interior waters. Although the two species overlap and often form mixed flocks, our area is not usually included in the range maps for greater scaup. However, we do live in one of the few spots in the US West where the lesser scaup is a year-long resident rather than migratory. I always attempt to look carefully when I see a scaup, but the odds are good that one near our home is a lesser scaup.
The lesser scaup, in addition to a black head has a black chest and rear end. The sides are white with more or less fine dark streaking. Its back is a finely barred grey. Yellow eyes and a bluish bill with a black tip, or nail, complete the picture.
There are several possibilities for the derivation of the name scaup. My favorite, that it is from the Scottich scalp meaning clams, mussels or oysters, is appropriate because this medium-sized diving duck sifts through the bottom mud in search of mollusks (clams and mussels) or seeds and other parts of aquatic plants. Scaup also eat insects, crustaceans and small fish, particularly in the winter.
This scaup was photographed in Baum Lake (Shasta County CA). A male scaup is not difficult to identify. Determining the species is the problem.