The Black-headed Duck (Heteronetta atricapilla) is a South American duck found in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. It is the most basal member of its subfamily, Oxyurinae, lacking the stiff tail and swollen bill characteristic of its relatives. Typically resembling a diving duck, it is about 35 cm long, with males averaging 510 g and females 565 g. The male has a glossy black head and upper neck, while the female has a dark brown head and whitish throat.
This duck thrives in freshwater marshes, mainly where sedge (Scirpus californicus) is dominant. It is partially migratory, residing year-round in much of its range, and feeds by diving, mainly on seeds and snails. Uniquely, it is an obligate brood parasite, laying eggs in the nests of various host birds without harming them. After about 25 days of incubation, ducklings are precocial and independent shortly after hatching. The black-headed duck is usually silent but emits low calls during courtship.
