The Black-headed Duck is a South America

South America

South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

n duck allied to the stiff-tailed duck

Stiff-tailed duck

The stiff-tailed ducks are part of the Oxyurinae subfamily of ducks. All have, as their name implies, long stiff tail feathers, which are erected when the bird is at rest. All have relatively large swollen bills.These are freshwater diving ducks...

s in the subfamily Oxyurinae

Oxyurinae

Oxyurinae is a subfamily of the duck, goose and swan family of birds, Anatidae. It has been subject of considerable debate about its validity and circumscription. Most of its members have long stiff tail feathers which are erected when the bird is at rest, and relatively large swollen bills...

 of the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Anatidae

Anatidae

Anatidae is the biological family of birds that includes ducks, geese and swans. The family has a cosmopolitan distribution, occurring on all the world's continents except Antarctica and on most of the world's islands and island groups...

. It is the only member of the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 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

Diving duck

The diving ducks, commonly called pochards or scaups, are a category of duck which feed by diving beneath the surface of the water. They are part of the diverse and very large Anatidae family that includes ducks, geese, and swans....

, its plumage and other peculiarities give away that it is not a very close relative of these, but rather the product of convergent evolution

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

 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 swamp

Swamp

A swamp is a wetland with some flooding of large areas of land by shallow bodies of water. A swamp generally has a large number of hammocks, or dry-land protrusions, covered by aquatic vegetation, or vegetation that tolerates periodical inundation. The two main types of swamp are "true" or swamp...

s lakes and marshes in North Chile

Chile

Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

, Paraguay

Paraguay

Paraguay , officially the Republic of Paraguay , is a landlocked country in South America. It is bordered by Argentina to the south and southwest, Brazil to the east and northeast, and Bolivia to the northwest. Paraguay lies on both banks of the Paraguay River, which runs through the center of the...

, and North Argentina

Argentina

Argentina , officially the Argentine Republic , is the second largest country in South America by land area, after Brazil. It is constituted as a federation of 23 provinces and an autonomous city, Buenos Aires...

, feeding by dabbling on water plants and insects. The Black-headed Duck is of interest as an obligate brood parasite

Brood parasite

Brood parasites are organisms that use the strategy of brood parasitism, a kind of kleptoparasitism found among birds, fish or insects, involving the manipulation and use of host individuals either of the same or different species to raise the young of the brood-parasite...

 because the females never nest and lay their eggs in the nests of other birds instead, earning it the nickname Cuckoo Duck. The hosts are particularly the Rosy-billed Pochard (Netta peposaca), but also other ducks, coot

Coot

Coots are medium-sized water birds that are members of the rail family Rallidae. They constitute the genus Fulica. Coots have predominantly black plumage, and, unlike many of the rails, they are usually easy to see, often swimming in open water...

s (Fulica species), and occasionally even gull

Gull

Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...

s (such as the Brown-hooded

Brown-hooded Gull

The Brown-hooded Gull is a species of gull in the Laridae family. As is the case with many gulls, it has traditionally been placed in the genus Larus....

) and birds of prey. Unlike for example certain cuckoo

Cuckoo

The cuckoos are a family, Cuculidae, of near passerine birds. The order Cuculiformes, in addition to the cuckoos, also includes the turacos . Some zoologists and taxonomists have also included the unique Hoatzin in the Cuculiformes, but its taxonomy remains in dispute...

s, neither the chicks nor adults destroy the eggs or kill the chicks of the host. Instead, after a 21-day incubation, the ducklings fledge

Fledge

Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...

 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.