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American Association for the Advancement of Science

Bird 'mobsters' learn from their neighbors

When a cuckoo comes along, hoping to sneak one of its own eggs into a reed warbler nest, the warblers mount an impassioned defense, mobbing the parasitic birds while making loud, raspy calls and snapping their beaks.

The warblers perform this mobbing behavior because they don't want to be tricked into raising the cuckoo's young as their own, which, from the warbler point of view, is a waste of their energy.

New research shows that the warblers learn mobbing behavior by watching their neighbors. But, in a funny twist, they only bother to learn when cuckoos and not other birds -- are on the receiving end of the mobbing.

Nicholas Davies and Justin Welbergen of the University of Cambridge in the United Kingdom set up experiments in which young, inexperienced reed warblers watched their more experienced neighbors' behavior against both cuckoos and harmless, dummy parrots.

The nave warblers adopted the mobbing behavior after watching their neighbors fend off the cuckoos but not the parrots. These findings suggest that the warblers are primed to learn new behavior only when it corresponds to true threats.

This predisposition may benefit warbler populations over the long term, since behavior like mobbing can backfire if used in the wrong situation, by attracting predators, for example.


These findings appear in the 5 June 2009 issue of the journal Science.