Lesser scaup by similar-looking "Aythya" hybrids. Except for hybrids between the two scaup species, the most reliable mark is the black bill-tip of hybrids, whereas in the scaups only the very point ("nail") of the bill is black. This is even recognizable at considerable range, as the scaups' bills appear uniformly grey from a distance, whereas those of hybrids look two-colored. European hybrids typically involve the tufted duck ("A. fuligula"), yielding offspring that have a small nape crest unlike any European "Aythya" species. Female and immature hybrids typically lack the white bill base, except in those between lesser scaup and ring-necked duck,
Lesser scaup where the white extends to the eye region. But especially with juveniles, the bi-colored bill of hybrids is most diagnostic. Hybrid combinations that are known from the wild and resemble the lesser scaup are: In theory, each and every "Aythya" species is able to produce potentially fertile hybrids with any other, though due to their different ranges and behavioral cues given during courtship most of these hybrids are only known from birds kept in captivity without conspecific mates. Their breeding habitat is inland lakes and marsh ponds in tundra from Alaska through western Canada to western Montana; few breed east