Washington, Feb 1 : Cross River gorillas in Cameroon have been spotted hurling clumps of grass or tree branches at human intruders, a man-like behaviour which has never earlier been observed in the animal.
According to National Geographic News, researchers documented three cases in which the gorillas on Cameroon's Kagwene Mountain used the vegetation as "weapons" against human intruders, who had provoked them.
"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," she added.
In one of the three documented instances, the researchers observed a local hunter stumbling upon a group of gorillas. When the hunter tried to scare off the gorillas by banging his machete on the ground, the group stayed put.
The unexpected thing about the incident was that when the hunter began picking up stones and throwing them at the gorillas, the gorillas responded by picking up chunks of grass and throwing them back at the hunter.
"This went on for an hour," said Sunderland Groves. "The gorillas seemed more curious than frightened," she added.
As for an explanation for this unusual behaviour, scientists suggest that the animals might have learned it from interactions with humans.
According to the researchers, the highly endangered gorillas' mountainous habitat reaches into farms and the animals might have come into at least visual contact with humans fairly regularly.
"These gorillas are surrounded by so many people, maybe throwing things is part of their learned behavior," said Groves.
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.
Though the apes have been observed throwing objects at predators or rivals before, there is no documentation of western gorillas using tools in an aggressive way, which makes the Cameroon observations the first of its kind.
"This new observation certainly merits further follow up and contributes to our growing understanding of gorillas' tool-use abilities," said Elizabeth Lonsdorf, director of the Center for the Study and Conservation of Apes at the Lincoln Park Zoo in Chicago.