Cuckoo The cuckoo is perhaps the best-known brood parasite. Natural selection has resulted in mimicry—cuckoo eggs look like host eggs. Yet the cuckoo's egg generally hatches sooner and its nestling grows faster than those of the host. Cuckoo nestlings also fight for their place in the nest. The nestlings are known to wriggle under host eggs and chicks and tip them out of the nest. As the sole survivor, the cuckoo nestling then monopolizes the host parent's care. Caption: Don't be fooled by size: The wren (left) is foster mother to this cuckoo chick.