Orangutans can learn how to use stone tools as hammers and knives

Captive orangutans that had by no means seen stone instruments might work out methods to use them to hit or lower issues – however they couldn’t get the grasp of constructing them

By Michael Marshall

Captive orangutans that had by no means seen stone instruments have spontaneously picked up rocks and used them as hammers. One particular person additionally used a pointy stone as a reducing device.

The discovering means that even orangutans, which stay in timber and barely encounter stones, can work out methods to make use of them. However there are limits: the animals by no means realized to make their very own instruments out of uncooked stone, even after being proven how.

“We didn’t discover the orangutans might mix these behaviours,” says Alba Motes Rodrigo, who led this analysis whereas on the College of Tübingen in Germany.

Motes Rodrigo and her colleagues studied two male orangutans residing at Kristiansand Zoo and Amusement Park in Norway. The apes got a field containing a chunk of fruit, sealed with rope. They had been additionally given a concrete hammer and a lump of rock. In principle, the orangutans might have used the hammer to knock sharp flakes off the rock, after which used the flakes to chop the rope and attain the fruit. However they didn’t.

The orangutans did hit issues with the hammer, although. “We discovered percussion, which is fascinating as a result of orangutans within the wild very hardly ever work together with stones in any respect,” says Motes Rodrigo. The orangutans may need been taking part in, she suggests.

In a follow-up experiment, Motes Rodrigo gave the orangutans a flint flake sharpened into an axe-like device. “One particular person, after attempting to open the packing containers in several methods, did get this sharp stone axe that I had made myself and used it to chop open the field and procure the reward,” she says. “They’ll spontaneously, with none coaching, recognise {that a} sharp stone can be utilized for reducing and use it as such.”

According to that, in one other experiment Motes Rodrigo gave the orangutans sharp stones, then rewarded them with grapes in the event that they handed them again. This was meant to encourage the orangutans to mentally hyperlink sharp stones with rewards. Afterwards, the orangutan who had lower the rope now took a blunt lump of rock and “began banging it round”. This knocked some sharp flakes off it, so in a way the orangutan had made sharp instruments. Nonetheless, he didn’t do something with them, suggesting he nonetheless didn’t perceive what he had made.

In a last experiment, Motes Rodrigo confirmed three different orangutans methods to make stone instruments. However regardless of repeated demonstrations, they by no means managed it – though one did begin hitting the lump of rock with the hammer. “Clearly, simply remark was not sufficient for this,” she says. “There’s something else that’s lacking there.”

It might be that the orangutans can’t perceive the spatial relations concerned in shaping instruments, or can’t suppose far sufficient forward, she speculates.

Journal reference: PLoS One, DOI: 10.1371/journal.pone.0263343

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