Cracking! Thailand’s macaques hang out on island beaches, cracking open seafood with stones Lydia Luncz

The macaques of southern Thailand have started a new tradition. For at least a century, they have used simple stone tools to smash open shellfish on the seashore. Now the monkeys have begun using stones to crack open oil palm nuts further inland.

The finding means they may be the first non-human primates to have begun adapting their Stone Age technology to exploit a new ecological niche.

Tool use is common in the animal kingdom, but very few animals make routine use of stones as tools. Among non-human primates, just three species are known to do so: the western chimpanzees of West Africa, the bearded capuchins of Brazil and the long-tailed macaques of Thailand. However, in all three cases biologists thought the primates restricted their stone tool use to a specific environmental setting.


“The chimpanzees live in tropical rainforest, and the capuchins in a dry savannah area,” says Lydia Luncz at the University of Oxford. And the macaques spend a lot of time on the beaches of Thailand’s islands, where they use stones to break into shellfish.

But the macaques also roam inland. In 2016, Luncz and her colleagues trekked through Yao Noi Island into an abandoned oil palm plantation. They found what appeared to be stones that had been used as hammers and anvils associated with broken oil palm nuts.

Crackers for nuts

The researchers set up camera traps near the anvils and scattered unprocessed palm nuts nearby. Over a three-week period the cameras recorded both male and female long-tailed macaques visiting the sites. The macaques placed nuts one at a time on the stone anvils and then struck them with the stone hammers until they broke, exposing the nutritious kernel.

A stone hammer and anvil, as used by macaques Courtesy of Lydia Luncz

“We know the macaques use stone tools at the shore – we believe they have transferred that behaviour to a new food source,” says Luncz. “They’ve applied what they know from the shore to a different ecosystem.”

What makes the behaviour all the more remarkable, says Luncz, is that humans only introduced oil palms to the area about 13 years ago. “So this is the first nut-cracking macaque generation on the island,” she says.

Luncz and her colleagues want to work out how the new tradition began. They hope to find older, abandoned sites where the macaques exploited the nuts a few years ago. Then it might be possible to work out how – or if – the monkeys have modified their use of stone tools as they have learned to exploit the oil palm nuts.

Nut now, I’m busy Courtesy of Lydia Luncz

“If we can distinguish those early tools from those now used after years and years of practice, we might see an evolution within the tool,” says Luncz.

Adaptable monkeys

It’s an important finding, says Dorothy Fragaszy at the University of Georgia in Athens. Chimpanzees and humans are also known to use stones to crack oil palm, so cross-species comparisons are now possible.

“They could manage the problem in a similar way,” says Fragaszy. “Or they could adopt different strategies for cracking the nut, depending on their perception of the relation between their movements and the outcome of a strike, and their control of their movements.”

The finding is not surprising, though, says Elisabetta Visalberghi at the Institute of Cognitive Sciences and Technologies in Rome, Italy. Macaques are known to adapt well to different environments. “When their range covers cities or cultivated areas, they exploit the food available there with the manipulative behaviours that they are capable of.”

Visalberghi also points out that the macaques have been observed cracking sea almonds produced by trees along the shore, so it is less of a mental stretch for them to begin cracking oil palm nuts inland.

Our distant hominin ancestors also used simple stone hammers to process foods, and might have adapted those tools to different ecological niches as they expanded and became more successful. “A next step might be to look at whether the long-tailed macaque is a good model for what might have happened in early hominin stone tool use,” says Luncz.

Journal reference: International Journal of Primatology, DOI: 10.1007/s10764-017-9985-6

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