The Sulawesi Cuckoo (usually referred to as the Sulawesi Hawk-Cuckoo, but more related to the Typical Cuckoos) is endemic to Sulawesi Island, in Indonesia. Like the other Cuckoos, this species is what’s known as a brood parasite. While a nest is unattended by the occupants, they’ll come in, lay an egg, and leave. This is then repeated with several other nests in the area, until the clutch is laid. Depending on the species, the adult cuckoo may eject the occupant’s eggs prior to laying her own, or the cuckoo chick may eject its nest mates once it hatches.
Because the chicks of brood parasites are larger and hatch earlier than the host’s eggs, they divert all attention from the host’s eggs. Birds (passerines especially) are pretty much “hey there’s a screaming chick, better feed it”, so little songbirds sometimes end up caring for and raising these big ol’ cuckoo chicks without knowing something’s off. Or maybe they do know and just can’t do anything about it, but who am I to tell? Host birds are at least clever enough that if a female cuckoo lays her egg in the nest of a bird that has differently-colored eggs from her, they other bird typically ejects the cuckoo egg and lays another clutch of her own.
Transactions of the Zoological Society of London. 1874.