Rather than reproducing themselves, some birds choose to make sure the family genes are passed on by protecting the nests of their close relatives.
A new study shows that 9 percent of all bird species include non-breeders that help drive off birds like cuckoos, which lay their eggs in the nests of other birds.
“Birds like cuckoos are called brood parasites, which means they are reproductive cheats. They lay their eggs in the nests of other birds, imposing the costs of rearing on their hosts, who often lose their entire brood of chicks as a result,” says Naomi Langmore the lead investigator at Australia National University.
“Biologists have long wondered how this strategy, termed cooperative breeding, could be evolutionarily successful,” she says.
“When it comes to guarding the nest, if there is extra help for the breeding pair, it enhances protection against brood parasites, and the chances that their own chicks will survive,” say Michelle Hall and Raoul Mulder, coauthors on the study from the department of zoology at the University of Melbourne.
For the study, published in the journal Science, researchers looked at data from over 100 families of superb fairy wrens living at Serendip Sanctuary, near Melbourne and Campbell Park, near Canberra.
Extended bird families
The data showed that nests of larger family groups were less likely to contain cuckoo eggs than nests of small family groups.
Experiments with model cuckoos conducted at Serendip Sanctuary showed that bigger host groups of birds aggressively mob the invading cuckoos at their nests much more than smaller groups.
The global distribution of cooperative breeders and brood parasites is tightly linked and concentrated in two major geographic hotspots: Australasia and sub-Saharan Africa, says Hall.
“Understanding this interaction between cooperative breeding and brood parasites also helped explain the uneven global distribution of cooperative breeding birds.”
Source: University of Melbourne