Editing Lesser scaup (section)

====Hybridization====
Particularly in the case of vagrant birds in Europe, the identification is complicated by similar-looking ''[[Aythya]]'' [[hybrid (biology)|hybrid]]s. 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, 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:
* The occurrence of hybridization between lesser and greater scaup in the wild is disputed. Such hybrids could only be identified with certainty by [[DNA sequence]] comparison however. But while they may exist unnoticed, they cannot be frequent, as the species are largely [[sympatric]] and closely related, yet remain distinct, with no signs of significant [[introgression]].
* Hybrids between lesser scaup and ring-necked ducks are recognizable by very dark wings contrasting with a light grey underside more than in the lesser scaup but less than in the ring-necked duck.
* Hybrids between the lesser scaup and the [[redhead (duck)|redhead]] (''A. americana'') are recognizable by the lack of contrast between wings and belly and the dull brownish head.
* Hybrids between the tufted duck and the [[common pochard]] (''A. ferina'') are almost indistinguishable from lesser scaup, though neither parent species resembles ''A. affinis''.
In theory, each and every ''Aythya'' species is able to produce potentially [[fertility|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.<ref name = carboneras1992 /><ref name=Madge/>