for National Geographic News
The discovery has raised chatter among primate researchers, who say it's the first known case of regular cave use by an ape species.
The unusual behavior is shown by the same chimpanzees recently found to hunt small mammals using sharpened sticks.
Jill Pruetz, an anthropologist at Iowa State University, led the research team behind the new discoveries. Hers is the first long-term observational study of a savanna-dwelling chimpanzee population.
Pruetz said that when she began fieldwork in 2001, at a site known as Fongoli, local Malinke people showed her the caves and told her they were often occupied by chimpanzees during the hottest part of the year.
She was intrigued by the claim, but observing the chimpanzee behavior proved difficult.
"It took years and years for the chimpanzees to get habituated [to the researchers' presence]," Pruetz said. "As soon as we would walk anywhere close, it would scare them out of the caves."
Even with few direct observations, Pruetz's team was able to assess the extent of cave use using clues left behind on sandy cave floors: tracks, droppings, and food remains.
The research showed that cave use was concentrated at the end of the dry season in May and June.
"The behavior appears to be an adjustment to heat stress," Pruetz said.
"No one has ever before published reports of apes in caves," noted William McGrew of Cambridge University in England.
"This is one of those cases in which the apes genuinely surprise us, exceeding our expectations and imaginations."
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