As the unwary cichlid mom gathers her own eggs into her mouth to brood, she scoops up catfish offspring too. The catfish develop faster, hatch earlier, and then eat their foster siblings. Some ornithologists have estimated that this practice, called brood parasitism, has evolved at least seven times in birds. Some parasites, like the commom cucko, mimic the shading and speckling on the foster parents' eggs. Others, like the cowbird, get away with outrageous mismatches, leaving their cream eggs with black speckles even in nests of solid blue eggs.
Parasitic nestlings range in behavior from piggish to truly murderous.
Some of the cowbirds triumph over their nest mates by merely eating more than their share. Newly hatched honeyguides peck their nestling competition to death with heavy, hooked bills. Not all of the five cowbird species are total deadbeats as parents. Bay-winged cowbirds in South America sometimes take over a nest built by another bird, but they do raise their own offspring. In turn, however, their nests can be parasitized by the screaming cowbird.