Cowbird Cowbirds deposit their eggs in the nests of over 220 bird species. If the egg is accepted into the brood, the cowbird doesn't disrupt the family further. But if the egg is rejected, cowbirds trash the nest, destroying the host's eggs. This brutal behavior led ecologists to dub the species "mafia birds." Cowbird eggs hatch earlier than host eggs, and although the parasitic hatchling rarely attacks other nestlings, it cries louder, demanding a greater share of the food—which it almost always gets. This frequently leads to the starvation of host nestlings. Caption: This cowbird nestling (right) is poised to outcompete its companion wren host nestling.