Black headed duck

The black-headed duck (Heteronetta atricapilla) is a South American duck allied to the stiff-tailed ducks in the subfamily Oxyurinae of the family Anatidae. It is the only member of the genus Heteronetta.

This is the most basal living member of its subfamily, and it lacks the stiff tail and swollen bill of its relatives. Overall much resembling a fairly typical diving duck, its plumage and other peculiarities indicate it is not a very close relative of these, but rather the product of convergent evolution in the ancestors of the stiff-tailed ducks. It is a small, dark duck, the male with a black head and mantle and a paler flank and belly, and the female pale brown overall.

They live in swamps lakes and marshes in northern Chile, Paraguay, and northern Argentina, feeding by dabbling on water plants and insects. The black-headed duck is an obligate brood parasite (meaning the female does not build a nest). It lays its eggs in the nests of other birds, instead, earning it the nickname cuckoo duck. The hosts are (particularly) rosy-billed pochard (Netta peposaca), other ducks, coots (Fulica species), and occasionally even gulls (such as the brown-hooded gull) and birds of prey. Unlike some cuckoos, neither the chicks nor adults destroy the eggs or kill the chicks of the host. Instead, after a 21-day incubation, the ducklings fledge and after a few hours are completely independent, leaving their broodmates and fending for themselves, because the brood parasitic passerines (family Viduidae and genus Molothrus) are altricial, while black-headed duck ducklings are precocial.

The black-headed duck is not considered threatened by the IUCN.