for National Geographic News
"Oh hey, what's that over there?"
This classic means of distracting someone might not work so well among human thieves. For tufted capuchin monkeys, however, the trick could be a clever way to snatch a free meal.
Anthropologist Brandon Wheeler wanted to know whether the fruit-eating monkeys engaged in tactical deception, a practice thought to be important in primate evolution.
So he set up platforms in the trees of Argentina's Iguazú National Park and filled them with highly prized banana slices.
As the tufted capuchins ate together, individuals of relatively low social rank—which didn't always have access to the food—would sometimes make loud alarm calls to warn the rest of the group of an incoming predator.
But usually there was no danger in sight, Wheeler found. Instead, when nearby monkeys dropped their food and ran, the one that had sounded the false alarm moved in to scoop up the bounty.
Monkey Curse Word?
The scientists aren't yet sure whether such trickery is truly intentional, said Wheeler, a graduate student at Stony Brook University in New York State.
It's possible a monkey really thinks some threat is present when it sounds the alarm. But the caller quickly realizes that there's no danger and redirects its attention to the food, Wheeler speculated.
After this happens a few times, a monkey might learn to repeat the behavior even when the animal is sure there are no predators around—but that remains to be proven.
It's also possible that the alarm call isn't meant as an alarm but is "kind of like a monkey curse word," Wheeler said.
(Related: "Monkeys Use 'Sentences,' Study Suggests.")
The monkeys normally scream the call in high stress situations such as predator encounters, he explained.
"I suspect that these feeding situations are stressful for subordinate individuals, because they sit there and watch dominant individuals eat delicious food but have little chance of getting any themselves," Wheeler said.
The stress may build up to the point where a monkey reacts vocally, and others mistake the outburst as an alarm. Measuring the monkeys' stress hormones, he said, might help the researchers find out if this is the case.
Findings published online June 3 in the journal Proceedings of the Royal Society B.
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