Chimpanzees Observed Using Spears to Hunt Other Primates

A recent study in the scientific journal Current Biology has documented reports by researchers who were studying groups of wild chimpanzees in Fongoli, Senegal, between March 2005 and July 2006. The researchers made a startling discovery. In 22 separate cases, chimpanzees were observed fashioning wooden tools to jab and poke at smaller primates who were hiding in hollow tree trunks.

The authors of the study, which was funded by the National Geographic Society, were Jill Pruetz and Paco Bertolani working with the Leverhulme Centre for Human Evolutionary Studies in Cambridge, UK. The authors concluded that their findings were so startling that they could have wider implications in the context of human evolution, because chimpanzees have never before been observed using tools to hunt other animals.

Pruetz, who is assistant professor of anthropology at Iowa State University, said that in other research studies there had been hints that this behavior might occur, but it was never actually documented. However, she said, "While in Senegal for the spring semester, I saw about 13 different hunting bouts. So it really is habitual."

In most of the cases observed by Pruetz and Bertolani, the chimps broke off a living branch from a tree, trimming the side branches and leaves to make a spear. They carried out four or five steps to manufacture the spear, sometimes also trimming the ends of the branch and stripping off the bark. Occasionally chimps used their teeth to sharpen the tip of the spear.

After fashioning the tool, the chimps used it more as a spear rather than just a probe. Pruetz and Bertolani wrote that they observed the chimps poking into holes with enough force that any animal hiding inside would have been injured. The chimps jabbed the spears repeatedly, over and over again into caverns in trees. After removing the tool from a cavity, a chimp would often lick the end of it or smell it. In one case, the researchers witnessed a chimpanzee using a spear to extract a bushbaby from a hollow tree. However, they did not photograph the activity or document it on film in any way.

One caveat stated by the researchers in terms of the Senegal study is that many areas where chimpanzees live are also inhabited by the colobus monkey, which is a favorite prey of chimpanzees. But there are no colobus monkeys in Senegal, so it may be that the chimpanzees there had to adopt a new strategy for hunting in order to catch bushbabies, who frequently hide in tree cavities and nooks.

Another startling discovery by Pruetz and Bertolani was that more often that not, the fashioning of spears and using them to hunt was carried out by females, particularly adolescent females. Scientist have long believed that adult males are the principal hunters in chimpanzee groups. "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," said Dr. Pruetz. "The last ones to pick up are adults, mainly the males."

The reason for this, according to Dr. Pruetz, is that young chimps spend a lot of their time with their mothers, and they learn skills such as these from their mothers. "It’s a niche that males seem to ignore," said Pruetz. In conclusion, the authors suggest that their findings from the study might support the theory that human females may have played a similarly important role in the evolution of tool technology during the development of the human race.