The black-headed duck (Heteronetta atricapilla) is a South American duck in subfamily Oxyurinae of family Anatidae. It is found in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay.
Taxonomy and systematics
The black-headed duck is the only member of genus Heteronetta and has no subspecies. It is closely related to the "stiff-tailed" ducks of genera Nomonyx, Oxyura, and Biziura. its plumage and other peculiarities indicate it may not be a very close relative of the other stiff-tailed ducks, but rather the product of convergent evolution from the ancestors of the stiff-tailed ducks.
The black-headed duck is about long. Males weigh an average of about and females . The species has a distinctive shape, with a long body and disproportionately short wings. Its bill has a black maxilla and an orange mandible; the maxilla has a rosy patch at its base during the breeding season. Adult males have a glossy black head and upper neck and a white chin. Their upperparts are deep brownish black with cinnamon or pale rufous speckles and vermiculation. The folded wing shows two white bars. Their underparts are whitish with brown mottling and appear silvery. Adult females have a dark brown head and neck and a whitish throat, and are otherwise like the male. Immature birds are similar to the female but have more rufous upperparts, more yellowish underparts, and a pale eye stripe.
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File:Heteronetta atricapilla 117507900.jpg|Male
File:Heteronetta atricapilla 250320228.jpg|Female
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Distribution and habitat
The black-headed duck has two separate ranges. One is the western side of central Chile. The other is from extreme southern Bolivia south through central Paraguay to central Argentina and east through southern Uruguay into southernmost Brazil.