Birds learn from neighbours how to defend nests

June 5th, 2009 - 2:04 pm ICT by ANI  

Washington, June 5 (ANI): A new study by scientists at the University of Cambridge has shown that inexperienced reed warblers learn how to stop cuckoos from laying eggs in their nests by watching how other members of their species deal with the parasitic birds.

Reed warblers live with the threat that a cuckoo will infiltrate their nest, remove one of their eggs, replace it with a cuckoo egg, and leave cuckoo chicks to be raised by the unsuspecting reed warblers.

New experiments show that reed warblers will attack or “mob” cuckoos on their territory to prevent them from laying eggs in their nests and inexperienced birds learn from observing the mobbing behaviour.

This social learning was specific to cuckoos but not to harmless control birds, such as parrots, suggesting that the warblers are primed to learn defensive behaviour only in response to true threats.

“Our previous work showed that reed warblers distinguish cuckoos from other nest enemies and adjust their defences according to local parasitism risk. Our current work demonstrates that reed warblers can use social information to fine-tune their defences to the nature of the local threat,” said Dr. Justin Welbergen, co-author of the study.

It had previously been established that cuckoos (the parasites) and reed warblers (the hosts) are engaged in a co-evolutionary arms race. Once one had evolved an advantage, such as the reed warblers’ ability to eject the cuckoos’ eggs from their nests, the other would evolve a counter tactic, such as the cuckoo evolving eggs similar to those of the warbler.

However, although genetic adaptations were to be expected, it was a surprise to the scientists that social learning provided another mechanism by which the warblers rapidly increased their nest defence.

“Studies of co-evolutionary arms races between brood parasites and hosts have emphasized genetic adaptations and counter adaptations; however, our field experiments show that transmission through social learning provides a mechanism by which hosts can adjust their nest defence and so respond rapidly to changes in parasitism,” Welbergen said.

The findings are reported in June issue of the journal Science. (ANI)

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