For the first time, researchers have observed wild chimpanzees making and using tools for hunting. What’s more, it’s mostly the female chimps and juveniles that adopt this style of attack, which occasionally nabs a small mammal that the chimp then eats.
The discovery that tool-assisted hunting among chimps includes females and youngsters challenges the traditional idea that such behavior in people and their ancestors evolved as a solely male pursuit, say anthropologists Jill D. Pruetz of Iowa State University in Ames and Paco Bertolani of the University of Cambridge in England.
Pruetz and Bertolani studied 35 chimps living at Fongoli, a savanna site in southeastern Senegal. Between March 2005 and July 2006, the researchers recorded 22 instances of tool-aided hunting. In these cases, individual chimps made spearlike tools out of tree branches and then thrust the implements into cavities in hollow tree trunks and branches where bush babies sleep during the day.
Although most of the observed hunting attempts failed to snare the palm-size mammals, the investigators recorded one instance of a female chimp immobilizing a bush baby by jabbing it with a sharpened branch, pulling the animal out of its nest, and eating it.
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Chimps at Fongoli followed as many as five steps in fashioning their weapons, Pruetz and Bertolani report in the March 6 Current Biology. After inspecting a tree cavity and breaking off a branch about 0.6 meter long, chimps trimmed off leaves and side branches, frequently stripped bark off the branch, and used their teeth to sharpen one end into a point. Of the 10 chimps that used these tools to hunt bush babies, only one was an adult male.
At other sites, researchers have reported that teams of male chimps, using only their hands and mouths, hunt and kill red colobus monkeys and then divvy up the meat. Male chimps at Fongoli similarly hunt vervet monkeys that live nearby, Pruetz says.
The foresight and intelligence of Fongoli chimps wielding sharpened branches to disable tiny but elusive prey probably matches that of human ancestors living more than 3 million years ago, the scientists assert. However, archaeological sites rarely preserve tools made of wood. The oldest such weapons yet found are 400,000-year-old wooden spears unearthed at a German site.
Hunting with makeshift spears at Fongoli represents “yet another example of chimpanzee cultures,” comments anthropologist Linda F. Marchant of Miami University in Oxford, Ohio. She says that different chimp communities develop unique behavioral traditions much as human groups devise distinctive customs (SN: 9/3/05, p. 158: Available to subscribers at Chimps ape others to learn tool use).
In the late 1970s, bits of bush baby bones turned up in fecal studies by Marchant and her colleagues at a site near Fongoli. The researchers concluded that chimps ate bush babies, although the team observed no hunting such as that now reported at Fongoli.
“We want to compare this surprising behavior of the Fongoli chimps to that of chimps living in other habitats,” Pruetz says.
Anthropologist Adrienne Zihlman of the University of California, Santa Cruz says that the new evidence supports her view that females played a major role in the evolution of tool use. The Fongoli study shows that “females are innovators, socially central, and maintain traditions because they nurture and socialize the young,” she says.