for National Geographic News
Researchers have observed and photographed wild gorillas using sticks and stumps to navigate a swampy forest clearing in the Republic of the Congo. The images provide the first documented use of tools among wild gorillas.
In one instance, a female gorilla named Leah tried to wade across a pool of water but found herself waist deep after just a few steps. She retreated, grabbed a branch sticking out of the water, and used it to gauge the water's depth before wading deeper.
According to the researchers, Leah repeatedly tested the depth as she walked about 33 feet (10 meters) out into the pool, before returning to shore and her wailing infant.
In another instance, a female named Efi detached a stump from a bush and used it for support as she dug for herbs. She then made a bridge with the stump to help her cross a muddy patch of ground.
"It was quite surprising to me and my team to make this observation," said Thomas Breuer, a conservation biologist with the New York-based Wildlife Conservation Society, in an e-mail interview.
Breuer is currently in Congo, where the observations were made at Mbeli Bai in Nouabal-Ndoki National Park.
The researchers report their observations in the October 1 issue of the journal Public Library of Science: Biology. The photographs will also be featured in the new National Geographic Television series Wild Chronicles, airing Saturday on PBS.
"This is a spectacular finding, new and astonishing, especially since gorillas have long been regarded as somehow less smart than the other great apes," Frans de Waal, director of the Yerkes National Primate Research Center at Emory University, commented via e-mail.
Craig Stanford, an anthropologist who studies ape behavior at the University of Southern California in Los Angeles, agreed that the finding is a great surprise.
"We didn't expect that at all," he said. "Gorillas don't do a lot of things other great apes do. They don't eat meat or hunt. They lead a more sedentary life."
Prior to this finding, all the other great apes had been observed using tools. Captive gorillas have been shown to use tools, but observing the behavior in wild gorillas has proven difficult.
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