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 give away that 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 North Chile, Paraguay, and North Argentina, feeding by dabbling on water plants and insects. The Black-headed Duck is of interest as an obligate brood parasite, never breeding itself but laying its eggs in the nests of other birds instead. The hosts are particularly the Rosybill (Netta peposaca), but also other ducks, coots (Fulica species), and occasionally even gulls and birds of prey. Unlike for example certain 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 after a few hours and are completely independent, leaving their broodmates and fending for themselves.
The Black-headed Duck is not considered threatened by the IUCN.