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. See more
videos.