Honeyguides Kill Eggs of Own Species to Eliminate Competition

The Honeyguides, just like cuckoos, trick other birds into raising their young. Parasitic birds lay their eggs in other birds' nest and also destroy the host bird's nest to avoid competition. A new study from Cambridge University has found that the honeyguides will even destroy eggs of their own species to eliminate competition for the nest.

Honeyguides (Indicator indicator) are a unique species. One striking feature of these birds is that newly hatched honeyguides murder chicks of the host parents. While the parents puncture the eggs, the chicks kill the young birds with their sharp beaks.

Parasitic birds like cuckoos lay eggs that look like the eggs of the host so they don't realize they are raising a foreign egg. The honeyguides' eggs strongly resemble other eggs of the host species as well.

Cambridge scientists Nick Davies and Michael Brooke suggested 25 years ago that honeyguides' ability to conceal their eggs in hosts' nest evolved to avoid in-species competition.

In the new study, researchers found that, in the wild, honeybirds even kill the young ones of their own species to eliminate competition.

Honeyguides have evolved to lay eggs that are the same size as the host's eggs (usually of a bird called the bee-eater). Bee-eaters are quite dumb and will take care of eggs that are of any size as they have zero differentiating prowesses. It does all the damage with utmost care because if it spoiled the nest too much, the birds would completely abandon the place.

In the experiment, researchers placed a larger foreign egg in a bee-eater's nest and waited for a honeyguide to come and lay its eggs.

They found that the honeyguides pecked more strongly at the foreign egg (the larger one) than the native egg. This experiment supported the hypothesis that honeyguides would kill eggs of their own species.

"I assumed honeyguide egg mimicry had evolved just like cuckoo mimicry, so was bowled over and baffled when little bee-eaters turned out to be pretty dim. When I played the honeyguide and experimentally parasitised their nests, the bee-eaters blithely incubated eggs even much larger than their own. So I was quite wrong, and mimicry probably hasn't evolved to dupe bee-eaters," said Dr Claire Spottiswoode from the University of Cambridge's Department of Zoology and lead author of the study.

"It was only when some of my experiments were parasitised by real honeyguides, and my experimental eggs were pecked to pieces, that the penny dropped - perhaps they need to look like bee-eaters or else other honeyguides will get rid of them, to avoid suffering the same grisly fate that they impose upon their hosts," Spottiswoode added.

"Under these circumstances it makes good sense that honeyguides have a lot to gain from tricking other honeyguides. But we still don't know why bee-eaters parents themselves are so undiscriminating, especially when they pay such high costs of being conned - all your offspring hacked to death, and over a month wasted raising the wrong chick!," Dr Spottiswoode said in a news release.

The study is published in the journal Biology Letters.