Wild bearded capuchin monkeys are more skilled than anyone in cracking nuts, shows a new study by Indian-American psychologist Madhur Mangalam.
The monkeys are known to use stone "hammers" to crack nuts.
The monkeys are quite careful about the amount of force delivered to those nuts.
They adjust the force applied with each strike based on the condition of the nutshell, making it less likely that they will end up smashing the tasty kernel inside.
"Wild bearded capuchin monkeys dynamically modulate their strikes based on the outcome of the preceding strike while using stone hammers to crack nuts," said Madhur Mangalam of the University of Georgia at Athens, US.
In the new study, the researchers videotaped 14 capuchin moneys cracking nuts.
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They carefully analysed the tapes to determine the height and velocity of each and every strike.
It typically takes several strikes with a stone to reach the nut inside.
"It was a 'eureka' moment when we realized that the monkeys modulated the strikes systematically according to the condition of the nut following the preceding strike," Mangalam pointed out.
They had expected the monkeys to maintain the force of their strikes within a certain range, or possibly to increase it until the nuts cracked.
"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," Mangalam concluded.
The study appeared in the journal Current Biology.