Keep still, you nut! Bearded capuchins open nutshells by placing them on a log or a stone and smashing down on them with a rock, as if using a hammer and
an anvil. But how do the monkeys keep the round nuts still on the surface before the rock comes down? To find out, a team of primatologists rolled some
palm tree nuts to see where each stopped, marked which surfaces were stable with a permanent marker, and then gave the nuts to capuchins in Piaui, Brazil.
The monkeys placed the nuts in the stable position at which they stopped rolling 84% of the time, the researchers report today in a study in PLOS ONE. The scientists say the monkeys seem to get information about which side is more stable by
tapping the nuts against the smashing surface before placing them down, an action that had seemed unrelated. This shows, they say, that the monkeys
skillfully know how to adjust each individual nut for optimal smashing, like a batter in baseball adjusts his swing for individual pitches.
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