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Study of chimps cracking nuts shows some are much better at it than others

A team of anthropologists at the University of Oxford's School of Anthropology and Museum Ethnography, working with a colleague from Chubu Gakuin University, in Japan, has found that some chimpanzees are better at cracking nuts than others in their same group.

In their paper in the journal Nature Human Behavior, the group describes how they studied thousands of video-recorded attempts by chimps to crack open nuts and what they learned about the chimps' behavior.

Prior research has shown that some chimpanzees have learned to use rocks to crack open nuts, allowing them to eat the insides. In this new effort, the researchers wondered if there are differing degrees of ability among chimps living in the same community. To find out, they studied 3,882 instances of 21 wild chimpanzees cracking open nuts. The videos analyzed by the team were captured by various researchers studying the chimps living in Bossou, Guinea from 1992 to 2017.

To successfully crack a nut, a chimpanzee has to first select a type of nut that can be cracked. Next, the chimp must place the nut on a flat rock in a position that helps to ensure that the nut will crack when struck, rather than fly off to the side.

Then, the chimp must select a rock of the proper size, shape and heft to use as the hammer. And finally, the chimp must be able to bring the rock down onto the nut in a way that will cause it to break open, or crack. Cracking nuts by chimps, the researchers note, is an example of tool use by chimps.

To measure nut cracking ability in chimps, the research team broke it down into five types of ability: how long it took, number of strikes per nut, success rate, number of times a strike moved a nut, and the number of times a chimp gave up on a rock and went to find another one.

In studying the videos, the researchers found clear evidence of some chimps demonstrating better nut-cracking skills. They also found some were truly bad at it—they took twice as long as average. They also noted that the chimps tended to get better at it as they got older. Males and females were also found to be equally adept.

The researchers suggest their findings may show that there are measurable differences in cognitive ability among chimps in a single community.