The Black-headed Duck (Heteronetta atricapilla) is a unique interspecific brood parasite among birds where the host species provides parental care for incubation only. Despite this unique system, there are few studies on this species biology and the list of hosts remains incomplete. We present information about breeding phenology of the Black-headed Duck and an updated list of hosts obtained from a comprehensive review of egg collections deposited in the most important natural science museums of Argentina. We include five new hosts to the list: Great Grebe (Podiceps major), Maguari Stork (Ciconia maguari), White-cheeked Pintail (Anas bahamensis), South American Stilt (Himantopus mexicanus), and Long-winged Harrier (Circus buffoni). We found that solitary nesting host species were more likely to be parasitized earlier during the breeding season than colonial nesting species. The Black-headed Duck has an extended breeding season in central Argentina (Aug–Feb) as it is able to use a variety of hosts that breed in different times during the breeding season. With this contribution, the new list rises to 23 documented hosts of the Black-headed Duck belonging to eight different waterfowl orders.