Reed Warbler feeding a Common Cuckoo chick by Per Harald Olsen. Some species of birds thrive not by carefully rearing their own young, but by pawning that task off on adults of other species. This is called Brood Parasitism.
Merops is a large genus of bee-eaters, a group of near
passerine birds in the family Meropidae. The members of this Old World
family are characterised by richly coloured plumage, slender bodies and
usually elongated central tail feathers.Source: Bird Photography