Wednesday, July 16, 2008

"About 56 of the Old World species and 3 of the New World species are brood parasites, laying their eggs in the nests of other birds. The best-known example is the European Common Cuckoo. The cuckoo egg hatches earlier than the host's, and the cuckoo chick grows faster; in most cases the chick evicts the eggs or young of the host species. The chick has no time to learn this behavior, so it must be an instinct passed on genetically.

Female parasitic cuckoos specialize and lay eggs that closely resemble the eggs of their chosen host. This also seems to have been aided by natural selection, as some birds are able to distinguish cuckoo eggs from their own, leading to those eggs least like the host's being thrown out of the nest."

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