Lesser scaup that looks strongly curved or even angular due to the small crest. When the birds raise their heads, these differences are most easy to spot, and after observing the two species in direct comparison it usually becomes easy to recognize. In fact, in alternate plumage the lesser scaup drake may appear identical in shape and size to a drake of the ring-necked duck ("A. collaris"); the black back and wings of that species are hard to confuse with the light ones of the lesser scaup male though. Particularly in the case of vagrant birds in Europe, the identification is complicated
Lesser scaup more often than those of the greater scaup—particularly during flight—but their call is weaker, a guttural "brrtt, brrtt". Lesser scaup are often hard to distinguish from the greater scaup when direct comparison is not possible, but in North America a large scaup flock will often have both species present. Females, juveniles and drakes in eclipse plumage are hard to identify; there is considerable overlap in length between the two species, but greater scaup are usually noticeably more bulky. Lesser scaup females and immatures tend to have less white around the bill, but this too varies considerably between individual birds. The