The Bird That Forges Eggs and Mimics Hawks

A common cuckoo doesn't just drop an egg and leave; it performs a high-speed heist. To ensure the egg is accepted, the female cuckoo mimics the appearance of a hawk to scare the resident bird away from the nest.

While the host bird hides from what it thinks is a predator, the cuckoo swoops in and replaces one of the original eggs with her own in less than ten seconds. Her eggs are biological forgeries, evolved to match the exact color, speckling, and size of the host bird’s species.

This isn't a random trick. Individual cuckoos belong to specific genetic lines called gentes, where each line specializes in mimicking one specific host bird, like a meadow pipit or a reed warbler. A cuckoo raised by a warbler will grow up to lay eggs that look exactly like warbler eggs.

Once the cuckoo chick hatches, the deception turns dark. The blind, featherless chick uses a specialized depression on its back to shove the host's real eggs or chicks out of the nest. It wants the entire food supply for itself.

To keep the "parents" working, the single cuckoo chick can mimic the begging calls of an entire brood of hungry babies. The exhausted host birds will continue to feed a giant intruder that eventually grows to be three times their size.