Europe's common cuckoo doesn't raise its own young. Instead, the mother lays an egg in another bird's nest, such as a reed warbler's, and leaves.
Soon after hatching, the cuckoo chick pushes the warbler's eggs or chicks out of the nest and is raised alone.
Then it fakes a crowd. Its rapid begging call sounds like a whole nest of hungry chicks, and the warblers feed it like one.