Zoologists have debated whether birds that look out for predators while the rest of their flock feeds are behaving selfishly or cooperatively. But few have asked why these winged watchmen draw attention to themselves by making particular calls.
Andrew Radford at the University of Bristol, UK, and his colleagues observed groups of pied babblers (Turdoides bicolor; pictured) in the Kalahari in Africa, and recorded the sentinels' sounds. Playing the calls back, they found that the group ate more when a watchman sang; the flock also spread out more and looked up less often.
Because the foraging gains of other birds seem to explain the behaviour, the authors argue that it is an example of cooperation. The close kinship between guard and guarded suggests that sentinel duty is a means by which individuals increase their genetic contribution to future generations.
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Animal behaviour: A reassuring tune. Nature 453, 4–5 (2008). https://doi.org/10.1038/453004f
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DOI: https://doi.org/10.1038/453004f
