Lesser Scaup

Aythya affinis

The Lesser Scaup and the Greater Scaup are difficult to distinguish, even for experienced observers. Head shape is one way to differentiate them, but winter habitat can help too. If seen in favorable light, during the breeding season in alternate plumage, there is a greenish sheen to the Greater Scaups’ head, while the Lesser Scaup’s sheen is purplish. If viewed in profile, the Greater Scaup’s head is rounded at the crown. The Lesser’s (if in an alert pose) is flattened behind the crown. When seen from a distance, such identifiers are difficult to sort out, and often experienced surveyors will list scaup species in their reports. The nail at the end of a duck’s bill is another useful diagnostic feature. You must have the bird in hand for a measurement. The Greater Scaup’s nail is wider. A more general guideline mentioned in the literature to differentiate the two species is that the Greater Scaup is more of a saltwater bird and the Lesser is more of a freshwater bird. However, this rule seems to break down on the Texas Gulf coast, where the Lesser Scaup is present in greater numbers during the non-breeding season.

During southern California winters, we often find Lesser Scaup on our inland lakes, and Greater Scaup in salt water environs, such as San Diego Bay. When I visited Texas, I learned the scaup gathered in large numbers on the saltwater lagunas between the barrier islands and the mainland were Lesser Scaup, and not the Greater Scaup I first assumed. It seems that winter habitat preferences differ between eastern and western scaup populations.

Pair bonds often occur on the winter grounds and last until the hens lay their eggs. Then the males collect in bachelor groups to molt, leaving the hens in charge of child-rearing. Most of these ducks breed in Alaska and western Canada, but others breed in the northern tier of the western states. They spend winters from the Pacific Northwest and mid-Atlantic coasts south through the southern USA, Mexico, and Central America, the West Indies and Caribbean and slightly into northern South America.

Taxonomists regard the Lesser Scaup as monotypic (i.e. there are no subspecies).

While I was winding up my 2005 Alaska adventure, I stopped at Midway Lake in east-central Alaska and met a Lesser Scaup hen with ducklings in tow. It was the only image of this species I collected on the expedition.