Brood parasitism

A shiny cowbird chick (left) being fed by a rufous-collared sparrow

A host species (Eastern phoebe) which takes no notice of egg appearance. So the brood parasite egg (brown-headed cowbird egg) does not need to look like the host eggs.

Brood parasites are animals, usually birds, which trick other species to raise their young. The best-known example is the cuckoo. Brood parasitism works because the parasite develops faster than the resident eggs, kills its nestmates and turfs them out of the nest. The adult birds cannot tell the difference in the young, and spend their time raising the offspring of another species. In some cases, the parasite has the ability to make the begging cheeps of the host species.

The strength of defences and counter-adaptation rely on the species' ability to evolve. Some host species have very strong rejection defences. This makes the parasitic species evolving to have very close mimicry. But in other species, hosts do not reject the foreign egg. As a result, the parasitic species shows no egg mimicry.

Similar methods are used by some fish and insects.

Brood Parasitism Media

• Shiny cowbird parasiting masked water tyrant in Brazil

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  Four clutches of reed warbler eggs, each containing one visibly larger cuckoo egg

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  Kirbyan mimicry, in which a brood parasite mimics its host

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  The goldeneye often lays its eggs in the nests of other females, one of 74 species of Anseriformes to do so.

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  A Eurasian reed warbler raising a common cuckoo

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  A black-collared starling feeding an Asian koel

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  The catfish Synodontis multipunctatus is a brood parasite of several mouthbrooding cichlid fish.

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  A cuckoo bee from the genus Nomada