Lesser and greater scaup are counted together in annual aerial surveys because the two species are hard to distinguish at a distance. There are, however, a number of differences. Size is one, as lesser scaup are about 20 percent smaller than greater scaup. Drakes of both species appear similar from afar, with dark heads, white flanks, and gray backs. But greater scaup have white on their primary and secondary feathers extending nearly to the tip of the wing, while lesser scaup only have white on their secondaries. Up close, the drake lesser scaup's head has a purplish iridescence, while the sheen on the greater scaup's head is green. The greater scaup also has a rounder head, wider bill, and larger black nail at the tip of the bill. Both hens are brown with a white crescent patch at the base of their bill.