Brood parasitism in birds

Ever been out on a bird walk and encountered birds exhibiting some extraordinary behaviours? Nature never ceases to amaze! Every moment outdoors has its surprises. Such was Jeam Agutu’s experience during a birding trip in Homa Bay. A White-browed Robin Chat feeding a Red-chested Cuckoo chick? Where did this relationship begin, and how did it happen?

This bird behaviour is called brood parasitism. It occurs when one bird lays eggs in the nest of another bird (the host). The host then plays foster parent to the chick of the parasitic bird. Brood parasitism occurs only in birds of different species. About one per cent of the world’s birds are brood parasites. They include some cuckoos, a duck, honeyguides, whydahs and indigobirds.

But how do they manage to lay their eggs in other birds’ nests? Brood parasites may spend long hours patiently watching their hosts’ nest, anticipating an opportunity. Time is of the essence when the chance arises. The brood parasite lays its eggs in quick succession.

Some species even remove some of the host’s eggs. Others lay identical eggs to their specific host, making it difficult for them to distinguish the intruder’s eggs.

The eggs of brood parasites develop quickly and are usually the first to hatch. The nestlings of some species even kill the young of the unsuspecting host bird to get all attention.

In the case of the Village Indigobird that lays eggs in the nests of Red-billed Firefinches, the young indigobirds and firefinches grow up and feed together.