For the care and feeding of its offspring, the common cuckoo outsources.
When she’s ready to lay an egg, a female Cuculus canorus swoops to the unattended nest of a smaller species. She then swallows one of the eggs that’s been laid there and lays one of her own—a behavior known as brood parasitism.
Sometimes potential victims revolt. The parents that inhabit the nest may mob the cuckoo mom, preventing her from dropping off her egg; they may push out cuckoo eggs before they hatch, or they may even abandon the nest.