Savannah chimpanzees, which can make weapons to hunt other primates for meat, can also seek refuge in caves, much like our earliest human ancestors.
New findings suggest the chimps apparently shelter themselves in caves to hide from the extreme African heat. The cave use was documented by visual observations and photographs.
Primatologist Jill Pruetz at Iowa State University in Ames and her colleagues research savannah chimpanzees (Pan troglodytes verus ). These dwell in environs much like those from which humanity's ancestors are believed to have emerged.
Specifically, the researchers investigated the Fongoli community of 35 savannah chimpanzees in southeastern Senegal, one of the hottest and driest habitats chimps live in today.
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Just finding the chimpanzees in their large, roughly 7,400-acre home range was very challenging at first, Pruetz recalled.
"Going for a week or 10 long days without seeing chimpanzees was normal at the beginning and, as you might imagine, very frustrating at times, especially during the dry season, when heat is such an issue for chimps and humans alike!" she told LiveScience.
The research into chimpanzees' possible use of caves began when Pruetz's field assistant Mboule Camara saw the apes coming from Sakoto cave, the largest cavern within the chimp's home range.
The cave is more than 15 feet deep and located at the head of a shallow ravine that was formed through water runoff from a plateau.
To determine why they might use the cave, Pruetz recorded temperature data within the cave as well as at the different habitats the chimpanzees used, such as the woodlands and grasslands.
She discovered that chimps most often use the stone cave as shelter during the hottest and driest times of the year, from October to May, findings detailed in an upcoming issue of the journal Primates.
It is the first study to document regular cave use by chimps.
Up to 10 degrees cooler
Between 2001 and 2004, average annual daily temperature within the cave was 75.5 degrees Fahrenheit, compared with 85.2 degrees in the woodland locales and 76.2 degrees in grassland areas, both located at the edge of the Sakoto ravine and roughly 100 feet from the cave.
The grasslands were probably cooler due to wind, Pruetz said.
"They'll bring food in and eat it in there and groom. They sort of just hang out and relax," Pruetz said. The chimps apparently used the caves during the day and not at night.
Pruetz recalled talking at a meeting in Japan about chimps using caves.
"Everyone was amazed," she said. "They thought it was great and no one had ever heard of anything like it, except that Jane Goodall actually came up to me after the talk — I was very excited of course — and she said that she heard of an incident in Mali where someone was doing a chimp survey and they surprised a bunch of chimps coming out of a cave."
"But that was the only other instance that anyone, as far as I know, has ever heard of (chimps in caves)," Pruetz said. "And if Jane Goodall hasn't heard of it, then I assume it it's not known to science."
Paleoanthropologist Adrienne Zihlman at the University of California at Santa Cruz told LiveScience: "These chimpanzees are dealing with conditions most chimpanzees don't have to deal with. They are giving a little window to some of the problems that have to be solved if you want to survive in the savannah, and are confronting the kinds of problems that our early human ancestors had to face."
Biologist Rob Shumaker at the Great Ape Trust of Iowa in Des Moines added, "These findings really point out the range of behavioral and cognitive flexibility that exists for chimpanzees."
"These results aren't seen at any other chimpanzee field site, stressing the idea that there's cultural variation between chimpanzees across sites," Shumaker told LiveScience. "They continue to surprise us and teach use new things."
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