What is a brood parasite?

A brood parasite is an animal that does not raise its own young – it relies on other animals to look after its babies. The most famous brood parasite is the Cuckoo because some Cuckoos lay their eggs in the nest of other species of birds.

The Cuckoo is a medium-sized bird in the Cuculidae family. Some species of Cuckoo raise their own young, but other species of Cuckoo do not. Scientists from Stanford University estimate that about 40% of Cuckoo species around the world are brood parasites, in which the female does not make a nest – instead, she lays her eggs in the nest of other species of birds. 

Birds, insects, and fish are often the types of animals that can be brood parasites. They use different methods to get other species to raise their young.

For example, some Cuckoos uses egg mimicry to trick another bird. The Cuckoo’s eggs look like the eggs of another bird – in size, colour, or shape – and the other bird (called the host bird) does not know the difference. Sometimes, the host bird can tell the difference and rejects a Cuckoo’s egg but pushing it out of the nest.

Some ducks and geese are brood parasites.

The Mochokid Catfish (Synodontis multipuncatus), from Lake Tanganyika, is a brood parasite. After the eggs are spawned, the host Catfish thinks that the eggs are hers and puts them in her mouth – this is called mouthbrooding. The eggs then hatch inside the host Catfish’s mouth before the host’s own eggs, because the baby Mochokid Catfish eat many of the host’s real eggs. The host fish spits out the hatched live babies and they become independent and look after themselves. Other fish, like the female Cyprinid Minnow (Pungtungia herzi), in Japan, lays her eggs in the same reeds as a host fish. The host fish then protects the eggs along with her own eggs.

There are also solitary Cuckoo Bees and Cuckoo Wasps that lay their eggs in the nest of other bees.

Scientists think that the reason Cuckoos are brood parasites is because it gives them more time for feeding and laying more eggs, instead of spending time raising their young, but this idea has not been definitely shown to be true. Some scientists think it might be due to protecting their eggs because their young would have a stronger chance of surviving with birds that are effective parents. 

However, the act of brood parasites is not clearly understood across all species. And while 40% of Cuckoos are brood parasites, Stanford University scientists estimate that ony about 1% of all the world’s species of birds are brood parasites.

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM