As if size and strength were not enough to scare off human intruders, gorillas may have another tactic at their disposal: improvised weapons.
Researchers studying western gorillas in Cameroon have documented three cases in which the great apes threw clumps of grass or tree branches at humans.
"At first we didn't think too much of it, but then we realized that this is quite remarkable," said Jacqueline Sunderland Groves, who established the Wildlife Conservation Society research team working in the area.
"I don't think gorillas have been documented using this kind of weaponry before in the wild."
The observations were made during a three-year ecological study of Cross River gorillas (Gorilla gorilla diehli) on Cameroon's Kagwene Mountain.
A paper describing the incidents was recently published in the American Journal of Primatology. In it, the scientists suggest that the animals might have learned their unusual behavior from interactions with humans.
Testing the Waters
Great apes have long been known to use tools. Many studies have shown that wild chimpanzees use a variety of objects, including sticks and rocks, for foraging and other activities.
(Related: "Chimps Use 'Spears' to Hunt Mammals, Study Says" [February 22, 2007].)
Even the throwing of objects at predators or rivals has been seen before—it is considered one of the six primary types of tool use among primates.
At the Limbe Wildlife Center in Cameroon, for instance, captive gorillas have been observed hurling stones and grit toward human visitors, something they may have learned from chimps housed next door.
But captive behavior can differ significantly from behavior in the wild—and observing behavior in wild gorillas is especially difficult, because few groups are habituated to human presence.
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