Monkey hammers | Day 258

Bearded capuchin monkeys (Cebus libidinosus) are more skilled than you probably realised. Our little Central American cousins are omnivores, subsisting largely on fruit, but small birds, insects, and even frogs are also on the menu.

So are nuts, even ones encased in really tough shells.

In fact, capuchins are notorious for their nut-cracking skill, using nothing more than just a hard surface – an anvil – and a hefty rock. Watch this video below for a lovely demonstration.

While capuchin monkeys cracking nuts with stones isn’t really news, recently scientists did discover something remarkable about this behaviour. There is a reason why it took that monkey in the video so long, and why it wasn’t smashing harder.

Last year two researchers from the University of Georgia spent some time in Piauı, Brazil, where they recorded videos of 14 wild capuchin monkeys cracking nuts on a log anvil, using stones that ranged in weight from 500 grams to slightly over a kilo. Each time, the monkeys took several strikes to crack open the nuts.

By using video analysis software, the researchers tracked two main parameters of each strike – how high the monkeys held the stone when poised for the hit, and the maximum velocity of the stone as it was striking down. The results were recently published in Current Biology.1 What they found was that capuchins don’t just whack nuts until they are open. Instead, they determine how much force the nut needs depending on how successful the previous hit has been, and how hard the nut is. Several moderate strikes are better than a single huge one, because there is a better chance to preserve the flesh of the nut. It also turns out to be more efficient in terms of energy use.

“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,” study co-author Madhur Mangalam explained in the press statement. “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.”

In other words, capuchins aren’t just adorable. They are also far more dexterous than we thought.


Show 1 footnote

  1. Sorry about the paywall. The abstract is pretty comprehensive though.

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