Chimpanzees Hunt Using Primitive Spears

Researchers have documented 22 cases of wild chimpanzees fashioning wooden spears to poke at smaller primates sheltering in cavities of hollow branches or tree trunks. Chimpanzees have not been previously observed hunting other animals with tools.

"There were hints that this behaviour might occur, but it was one time at a different site," said Jill Pruetz, assistant professor of anthropology at Iowa State University, US and the study's lead author. Pruetz and her colleague, Paco Bertolani, made the discovery at their research site in Fongoli, Senegal, between March 2005 and July 2006.

"While in Senegal for the spring semester, I saw about 13 different hunting bouts. So it really is habitual."

In one case, Pruetz and Bertolani, from the Leverhulme Centre for Human Evolutionary Studies in Cambridge, UK, witnessed a chimpanzee extract a bushbaby with a spear. In most cases, the Fongoli chimpanzees carried out four or more steps to manufacture spears for hunting. In all but one of the cases, chimps broke off a living branch to make their tool. They would then trim the side branches and leaves. In a number of cases, chimps also trimmed the ends of the branch and stripped it of bark. Some chimps also sharpened the tip of the tool with their teeth.

Adult males have long been regarded as the hunters in chimp groups, but Pruetz and Bertolani wrote that females, particularly adolescent females, and young chimps in general were seen exhibiting this behaviour more frequently than adult males.

"It's classic in primates that when there is a new innovation, particularly in terms of tool use, the younger generations pick it up very quickly. The last ones to pick up are adults, mainly the males," said Pruetz. This is because young chimps pick the skill up from their mothers, with whom they spend most of their time.

"It's a niche that males seem to ignore," said Pruetz.

The authors conclude that their findings support a theory that females may have played a similarly important role in the evolution of tool technology among early humans.

This study was published in the journal Current Biology.

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