|MadSci Network: Zoology|
For the brood parasite mother the advantage is that no energy is expended to raise the offspring. Also, one individual's offspring are spread across many parents, thereby increasing the chances that two offspring will survive to reproduce. As for limits to opportunities to parasitize many parasitic species get around this by not being species-specific in the nests they use. Individual birds are generally limited to the nests of specific host species but this does not necessarily hold for the parasitic species. Also, it appears that brood parasites tend to pick on smaller birds as hosts. This would allow higher population densities for the hosts as opposed to the parasites. Thus the brood parasites tend not to be limited by nest availability (natural selection has reinforced behaviors that limit host specialization). More generally, the process of laying eggs in a nest that is not one's own is actually quite common among birds. When individuals of the same species are involved this is referred to as "egg dumping" rather than brood parasitism. Genetic tests of offspring and their brood parents has indicated that many avian females do this. These genetic tests also indicate that paternity is not as clear cut as once thought. Even among birds where both parents raise the offspring one can find fathers caring for clutches that aren't their own.
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