<P> Brood parasitism relieves the parasitic parents from the investment of rearing young or building nests for the young, enabling them to spend more time on other activities such as foraging and producing further offspring . Bird parasite species mitigate the risk of egg loss by distributing eggs amongst a number of different hosts . As this behaviour damages the host, it often results in an evolutionary arms race between parasite and host as the pair of species coevolve . </P> <P> In many monogamous bird species, there are extra-pair matings resulting in males outside the pair bond siring offspring and used by males to escape from the parental investment in raising their offspring . This form of cuckoldry is taken a step further when females of the goldeneye (Bucephala clangula) often lay their eggs in the nests of other individuals . Intraspecific brood parasitism is seen in a number of duck species, where females often lay their eggs in the nests of others . </P> <P> Interspecific brood - parasites include the indigobirds, whydahs, and honeyguides in Africa, cowbirds, Old World cuckoos, black - headed ducks, and some New World cuckoos in the Americas . Seven independent origins of obligate interspecific brood parasitism in birds have been proposed . While there is still some controversy over when and how many origins of interspecific brood parasitism have occurred, recent phylogenetic analyses suggest two origins in Passeriformes (once in New World cowbirds: Icteridae, and once in African Finches: Viduidae); three origins in Old World and New World cuckoos (once in Cuculinae, Phaenicophaeinae, and in Neomorphinae - Crotophaginae); a single origin in Old World honeyguides (Indicatoridae); and in a single species of waterfowl, the black - headed duck (Heteronetta atricapilla). </P> <P> Most avian brood parasites are specialists which parasitize only a single host species or a small group of closely related host species, but four out of the five parasitic cowbirds (all except the screaming cowbird) are generalists which parasitize a wide variety of hosts; the brown - headed cowbird has 221 known hosts . They usually lay only one egg per nest, although in some cases, particularly the cowbirds, several females may use the same host nest . </P>

What kind of bird lays its eggs in another bird's nest
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