Thursday, February 19, 2009

Birds' strategic mobbing fends of parasitic invaders

When I first read this headline I was thinking fleas and lice – but we’re talking cuckoos. A study recently published looks at how reed warblers are further adapting to the attentions of cuckoos. Evolution has progressed to the extent that cuckoos now lay eggs similar to those of reed warblers so that they are not rejected. The strategy now employed by reed warblers to prevent their hosting a cuckoo chick is to ‘mob’ the invading female cuckoo thus preventing any eggs from being laid. However, it’s not simply a question of mobbing every cuckoo in sight. The study found that mobbing cuckoos in high-risk areas had the benefit of preventing laying, offset against the actions attracting predators. In low-risk areas there were no such benefits with mobbing appearing to attract further cuckoos (and predators).
The strategic defense employed by reed warblers – mobbing, or not, according to the likelihood of being parasitized – has been likened to a military ‘defense-in-depth-strategy’. Next it’ll no doubt be close body combat and guerrilla tactics throughout the reedbed.
Article appears in Current Biology

Reed warbler feeding a parasitic common cuckoo chick in a nest. (Credit: Photo Per H. Olsen/Wikimedia Commons, Public Domain Image)

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