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Some Birds Become 'Maiden Aunts' to Defend Relatives' Chicks against Cuckoos

Dec 20, 2013 06:09 AM EST
Cooperatively-breeding speckled warbler (left) feeding a black-eared cuckoo fledgling (right).
(Photo : David Cook/ Australian National University )

Birds know that there is safety in numbers, which is why some choose against laying eggs and instead become 'maiden aunts' to protect their relatives' chicks against cuckoos, a new study from Australia reported.

The study, conducted by biologists at the Australian National University and their colleagues at the University of Melbourne, found that birds have evolved co-operative breeding to protect their chicks against parasite birds such as cuckoos.

In about nine percent of bird species, some choose to take care of relatives' chicks instead of producing their own brood, according to Dr Naomi Langmore of the ANU Research School of Biology. Biologists often found it hard to explain such behavior.

Earlier research has shown that the cuckoo lays eggs in other birds' nest. Their hatchlings are born murderers, who instinctively push the hosts' eggs out of the nest.

The latest study shows that the maiden aunts help the species survive by fighting brood parasite birds.

The present study used 'superb fairy-wrens' (Malurus cyaneus) to understand cooperative breeding practice. Researchers found that Horsfield's bronze-cuckoo (Chalcites basalis) couldn't lay their eggs if there were three or four wrens guarding the nest. The wrens fought-off the invaders with intensity greater than that showed against hawks or brown snakes, The Australian reported.

"Hosts were able to escape parasitism more frequently when they mobbed together in a large group, rather than defending their nest as a breeding pair," Dr Langmore said in a news release.

The study is published in the journal Science.

In North America, the Scrub-Jay, Gray-breasted (Mexican) Jay, Groove-billed Ani, and Acorn Woodpecker adopt cooperative breeding, according to a Stanford University essay.

Cooperative breeding and brood parasitism is more common Australasia and sub-Saharan Africa.

"In these two regions, hosts of brood parasites are much more likely to be cooperative breeders than unparasitised species, suggesting that brood parasites could place pressure on host species to take up cooperative breeding to better defend themselves," Dr Langmore said.

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