Brood parasites are birds that lay their eggs in the nests of other bird species, leaving the host parents to raise their young. Brood parasitism is a fascinating reproductive strategy found in several different groups of birds.
Common Cuckoos
The most well-known brood parasites are cuckoos. There are about 140 species of cuckoos worldwide, and many of them are obligate brood parasites, meaning they rely entirely on brood parasitism for reproduction. Some of the most common cuckoo brood parasites include:
- Common Cuckoo – Found in Europe, Asia, and Africa, these birds parasitize a wide variety of small songbirds like warblers, pipits, and larks.
- Yellow-billed Cuckoo – Distributed across North America, these cuckoos lay their eggs in nests of robins, jays, and other mid-sized songbirds.
- Greater Roadrunner – Living in the southwestern United States and Mexico, roadrunners foist their eggs upon many species like the Western Scrub-Jay and Northern Mockingbird.
- Koels – There are several koel species found in Asia and Australia that practice brood parasitism on babblers, crows, and honeyeaters.
Cowbirds
Cowbirds are songbirds that belong to the genus Molothrus and are found exclusively in the Americas. There are seven species of cowbirds and all are obligate brood parasites. Some widespread cowbird brood parasites include:
- Brown-headed Cowbird – Parasitizes over 220 host species across North America including warblers, vireos, sparrows, and blackbirds.
- Shiny Cowbird – Found from Mexico to Argentina, they primarily parasitize larger birds like mockingbirds, thrashers, and finches.
- Giant Cowbird – Occurs in Central America and parts of the Caribbean. Parasitizes big hosts like oropendolas, grackles, and jays.
Honeyguides
Honeyguides comprise a family of near-passerine birds found throughout Africa, the Indian Subcontinent, and southeast Asia. There are 17 species of honeyguides, and all are highly specialized brood parasites that primarily lay their eggs in bee-eater and barbet nests. Some examples include:
- Greater Honeyguide – Occurs widely in sub-Saharan Africa and parasitizes species like barbets, woodhoopoes, and bee-eaters.
- Scaly-throated Honeyguide – Found across central and eastern Africa. Specializes on targeting bee-eater nests.
- Grey-headed Woodpecker – Ranges in the Indian Subcontinent and southeast Asia. Parasitizes barbets, koels, and woodpeckers.
Ducks and Geese
A number of waterfowl species practice brood parasitism including ducks, geese, and swans. The most notorious is the Black-headed Duck of South America which lays its eggs in the nests of coots, grebes, and other waterfowl. Some other waterfowl brood parasites include:
- Ruddy Duck – Parasitizes other diving ducks like canvasbacks, redheads, and lesser scaups in North America.
- Crested Duck – Found in South America, they utilize the nests of marshbirds like coots and gallinules.
- Barnacle Goose – Breeds in arctic regions and often dumps eggs in nests of similar geese species like brent geese.
Old World Sparrows
The subfamily Plocepasserinae features several species of finch-like Old World sparrows that engage in brood parasitism. Most of their hosts are other sparrow species or estrildid finches. Some examples are:
- Diederik Cuckoo – Distributed across Africa, they specialize on parasitizing various weaver species.
- Indian Sparrow – Found on the Indian Subcontinent, they utilize the nests of other sparrows and munias.
- Black-throated Finch – Occurs in Australia, parasitizing hosts like long-tailed finches and parrot finches.
Indigobirds and Whydahs
Indigobirds and whydahs are two groups of estrildid finches found throughout Africa that exhibit brood parasitism. All indigobird and whydah species parasitize specific grass finch or mannikin host species. For example:
- Pin-tailed Whydah – Parasitizes tawny-flanked prinias.
- Shaft-tailed Whydah – Specializes on parasitizing common waxbills.
- Village Indigobird – Lays eggs exclusively in nests of red-billed firefinches.
- Jambandu Indigobird – Parasitizes African firefinches.
Jacanas
Jacanas are tropical wading birds with long toes that allow them to walk on floating vegetation. One jacana species, the African Jacana, occasionally practices brood parasitism, laying eggs in nests of darters, herons, and other jacanas. They are the only shorebirds known to be brood parasites.
Conclusion
In summary, brood parasitism has independently evolved in several distantly related groups of birds including cuckoos, honeyguides, cowbirds, waterfowl, sparrows, and finches. It is an effective strategy that allows the parasites to reproduce without the costs of nest building and chick rearing. The behavior highlights the remarkable diversity of avian reproductive behaviors.