A brood parasite is an organism that relies on another organism to raise and care for its young.
In birds, the brood parasites are those species which lay their eggs in the nests of other species (known as host species). There are about 100 species which are brood parasites; that is close to 1% of all bird species!
The cuckoos are the best known brood parasites. In southern Africa the two best known and most widespread cuckoos are Klaas’s Cuckoo (which uses batises, warblers and sunbirds as hosts) and Diderick Cuckoo (hosts are mainly weavers, bishops and sparrows). There are about 60 cuckoo species which are brood parasites.
All 20 species in the family Viduidae (the whydahs, indigobirds and the Cuckoo Finch) are brood parasites. This family is endemic to Africa south of the Sahara Desert. Most the whydah and indigobird species have a single regular host species: Pin-tailed Whydah parasitises Common Waxbill; Shaft-tailed Whydah parasitises Violet-eared Waxbill; Dusky Indigobird parasitises African Firefinch, … In contrast to the other members of the family Viduidae, the Cuckoo Finch parasitises many species, mainly cisticolas and prinias.
The honeyguides are also brood parasites. They lay their eggs in the nests of a wide variety of species. There are 17 species of honeyguide, with 15 in Africa south of the Sahara Desert and two in southern Asia. Greater Honeyguide has been recorded using 20 hosts, all of which breed down holes, either in banks or trees, with African Hoopoe being most frequently recorded. They are all cavity-nesters. Lesser Honeyguide uses mainly the barbets as hosts.
Amazingly, there is a single duck species which is a brood parasite. The Black-headed Duck of southern South America lays it eggs in the nests of a variety of waterbird species, including the local species of coot.