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Doing Well by Doing Good

Watching out for others may not be a burden after all, at least for the African mongoose. In today's Science, researchers report that what some had touted as selfless behavior by the rabbit-sized mammal--keeping watch over its fellows as they dig for grubs and other food, and sounding an alarm when a predator approaches--is actually rather selfish.

Scientists had assumed that the willingness of a mongoose to stand guard was driven by the evolutionary benefits of protecting one's relatives, as sentinels were thought to be more visible--and vulnerable--to predators. But ecologist Peter Bednekoff of Eastern Michigan University in Ypsilanti questioned that assumption. He suggested that keeping watch might actually be the safest place in a group, because guards have more time to escape a predator. Accordingly, he predicted that few sentinels would be killed by predators, that a sentinel would be no more likely to guard its kin than unrelated mongooses, and that animals would be more likely to guard once they'd eaten their fill.

Zoologist Tim Clutton-Brock of the University of Cambridge and his colleagues field-tested these predictions in the Kalahari Gemsbok Park in South Africa. While logging more than 2000 hours observing mongoose groups, the researchers never saw a sentinel killed. Rather, most guards positioned themselves near a burrow and were the first to duck underground after sounding an alarm--their "watchman's song." Mongooses unrelated to others in a group spent neither more nor less time on guard duty, and animals were more likely to keep watch after they'd filled their bellies.

The paper shows "quite beautifully" that the altruistic mongooses have found ways to minimize the cost of their apparent selflessness, says behavioral ecologist Susan Alberts of Duke University. But, she notes, it does not explain why the animals don't return to their holes and rest--as truly selfish animals might--rather than guarding their groupmates and giving their watchman's song.