Chimps found using spears

Chimps found using spears

Feb. 22, 2007
Courtesy National Geographic Society
and World Science staff

Chimps in Senegal are regularly making and using spears to hunt
other, small primates, without human help, according to research
led by an anthropologist.

It’s the first study to report regular tool use by non-humans
while hunting other vertebrates, according to the U.S. National
Geographic Society, which helped fund the work.

Anthropologist Jill Pruetz of Iowa State University in Ames,
Iowa, and Paco Bertolani, a graduate student at the University of
Cambridge, U.K., documented 22 cases of chimps making spears to
use in hunting down smaller primates in cavities of hollow
branches or tree trunks.

Chimps made the spears of live branches that they trimmed, then
sharpened with their teeth, Pruetz and Bertolani said. They found
the activities at Fongoli, Senegal, in 2005 and 2006.

A paper on the findings is to appear in the March 6 issue of the
research journal Current Biology. The paper was online
biology.com/ content/article/ abstract? uid=PIIS09609822 07008019> in
the journal starting today.

“We came upon the discovery quite unexpectedly, ” said Pruetz.

“There were hints that this behavior might occur, but it was one
time at a different site. Then I talked to [Bertolani] and he
told me that he saw a female hunt with tools. When he looked
through original data… we realized he had other evidence and
observations of them probably doing the same thing. While in
Senegal for the spring semester, I saw about 13 different hunting
bouts. So it really is habitual.”

Chimps repeatedly jabbed tools into hollow trunks or branches and
smelled and/or licked them upon extraction, the researchers said.
Two of the 22 cases were judged as merely playful-in the case of
an infant male-or exploratory. In all other cases, the scientists
said the chimps poked with such force that prey could have been
injured. They described just one case in which a chimp extracted
a bushbaby, a smaller primate, using a spear.

Although hunting is predominantly an adult male activity with
chimps, only one adult male of 11 males in the chimp community
was seen in the tool-assisted hunting, the investigators said.
The rest were adolescent or younger chimps of both sexes.

“In the chimp literature, there is a lot of discussion about
hunting by adult males, because basically, they’re the only ones
that do it, and they don’t use tools,” said Pruetz.

“Females are rarely involved. And so this was just kind of
astounding on a number of different levels. It’s not only chimps
hunting with tools, but females-and the ones who hunted the most
with them were adolescent females.

“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,” she said. “This is because immatures learn from the
ones they are most affiliated with, their mothers.”

The findings support a theory that females might have played a
role in the evolution of tool technology among early humans,
Pruetz said. Those technologies would have included both hunting-
and gathering-related activities. “The combination of hunting and
tool use at Fongoli, behaviors long considered hallmarks of our
own species, makes the population especially intriguing,” wrote
the scientists in the Current Biology paper.

“The observation that individuals hunting with tools include
females and immature chimpanzees suggests that we should rethink
traditional explanations for the evolution of such behavior in
our own lineage. Learning more about the unique behaviors of
chimpanzees in such an environment, before they disappear, can
provide important clues about the challenges facing our earliest
ancestors.”