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A capuchin monkey eating a nut. Courtesy Tambako the Jaguar, flickr.

University of Georgia researchers looked into how the bearded capuchin monkey utilized tools, a skill which is rare in monkeys.

A distant ancestry to humans brought about interest in the bearded capuchin monkey’s use of tools, said Freya Liu, a graduate teaching assistant in the department of psychology and one of the co-authors of the study. Dorothy Fragaszy, the leader of the research and a psychology professor, said the rarity of tool utilization also helped spur research.

Liu said the study focuses on how the monkeys selected tools, social influences on tool usage and how monkeys carried their tools. Researchers examined behavior and compared it to that of humans.

Tool usage is more commonly attributed to chimpanzees, Liu said, which have a closer relation to humans. Four major species of monkey also use tools, Fragaszy said.

The team of researchers observed capuchin monkeys in Piauì, Brazil, focusing on how they used stone tools. The research centered on the use of large rocks to open palm nuts.

To open the nuts, the monkeys first created a small pit on an anvil-type rock surface. The palm nuts were then placed in the pit and cracked open with large rocks. Researchers marked the nuts with a line on the stop meridian in order to track the monkeys’ habits.

Each time the nut was placed in the anvil pit, the stop meridian was in the middle.

“They put it in with the stop meridian facing up almost all the time. They’re very consistent,” Fragaszy said.

In addition to consistency, the monkeys also showed immense strength. Each rock used by the monkeys was about a third of a capuchin monkey’s body weight.

“They can easily lift their own body weight. They’re really strong; they lift like Hercules,” Fragaszy said. 

Researchers conducted an experiment using the nuts with blindfolded humans, who also placed the nut with the stop meridian facing up.

Fragaszy said her team’s research on the skill of capuchin monkeys came from an interest in the skill involved in adjusting one’s action to accommodation.

“If you could only hit a ball when it was pitched in exactly the same way, we wouldn’t call you a skillful batter,” Fragaszy said. “That’s what I mean by skill.”