VIDEO: Scientists had a eureka moment when they studied monkeys using a stone hammer

Capuchin monkeys. Jeff J Mitchell/Getty Images

Wild bearded capuchin monkeys are more dexterous than first thought and carefully adjust the force when using a stone “hammer” to open a nutshell.

US scientists say this controlled hammering makes it less likely that the tasty the kernel inside comes out crushed.

Watch a monkey at work on a nut:

“Wild bearded capuchin monkeys dynamically modulate their strikes based on the outcome of the preceding strike while using stone hammers to crack nuts,” says Madhur Mangalam of the University of Georgia. “Until now, this level of dexterity was not suspected of any monkey.”

Mangalam’s graduate advisor, Dorothy Fragaszy, and her colleagues have studied nut-cracking in wild bearded capuchin monkeys since 2005.

The researchers videotaped 14 capuchin moneys cracking nuts and carefully analysed the footage to determine the height and velocity of each and every strike. It usually takes several strikes with a stone to reach the nut inside.

“It was a eureka moment when we realised that the monkeys modulated the strikes systematically according to the condition of the nut following the preceding strike,” Mangalam says.

“Our finding opens our eyes to the fact that non-human primates modulate their actions with a tool to accommodate the rapidly changing requirements of the task, which is a cognitive accomplishment.”

The research is published in the journal Current Biology.

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