Rock-wielding monkeys make adjustments when cracking nuts

STRIKE FORCE Wild bearded capuchin monkeys, such as this adult male, adeptly crack open nuts by adjusting the force of each blow made with a pounding stone, a new study finds.

D. Fragazy

By Bruce Bower

April 30, 2015 at 12:00 pm

Wild bearded capuchin monkeys have serious nut-cracking skills. These Brazilian forest-dwellers, already known to pound open nuts with stones, adjust the force of two-handed strikes so as not to smash the soft kernels inside, researchers report April 30 in Current Biology.

Videotapes of 14 monkeys cracking nuts enabled scientists to calculate the height and velocity of each blow. Monkeys needed a handful of stone strikes to remove the nuts’ soft outer hulls and hard inner shells.

Hungry primates didn’t bash nuts with all their might or whack increasingly harder until nuts cracked. Instead, monkeys altered the speed of moderately forceful strikes based on a nut’s condition after preceding strikes. Capuchins, it seems, prefer their snacks intact.

SNACK ATTACK A wild capuchin monkey demonstrates how to use a rock to remove a nut’s soft outer hull and hard inner shell.Mangalam et al./Current Biology 2015