These sneaky little birds lay their eggs in other species' nests, leaving someone else to raise their young. After choosing an unsuspecting victim, the female cowbird lurks about until the foster mom leaves her nest. Then the cowbird lays a single egg in the nest and ditches one of the eggs already there. Taking after mom's unscrupulous nature, cowbird nestlings squawk loudly to demand food at the expense of the other nestlings. Sometimes, the cowbird chicks even nudge their foster siblings out of the nest, where they fall to an untimely death.
Cowbirds prefer to hang out in open fields and parasitize many nests along forest edges.
Many forest songbirds have suffered huge population declines in recent years, in part because of flourishing cowbird numbers. A great pincushion waddling on stubby legs, Australia's short-beaked echidna resembles a cross between a porcupine and an anteater. Throwing her mammalian classification to the wind, the echidna mom lays one grape-sized, leathery egg straight into her own pouch. Mom seems gracious enough, until her wee one develops its spine 50 days later. Mom only comes to visit every five days or so, and each time she leaves, she buries her echidna toddler well.