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Chimps hunting with tools
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Jill Pruetz's study on Senegal chimpanzees is the first to
report habitual tool use by non-humans while hunting other vertebrates.
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Chimpanzees in Senegal are regularly making and using spears to hunt
other primates - without human assistance - according to research led
by Jill Pruetz, assistant professor of anthropology.
That study, funded by the National Geographic Society, is the first to
report habitual tool use by non-humans while hunting other vertebrates.
Pruetz and Paco Bertolani, a graduate student at the University of Cambridge
in England, documented 22 cases of the chimps fashioning tools to use
in hunting smaller primates in cavities of hollow branches or tree trunks.
They made the discovery at their research site in Fongoli, Senegal, between
March 2005 and July 2006.
A paper on the study, authored by Pruetz and Bertolani and titled "Savanna
chimpanzees (Pan troglodytes verus) hunt with tools," will be published
in the March 6 edition of Current Biology.
"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 my project manager (Bertolani)
and he told me that he saw a female hunt with tools. When he looked through
original data that was collected, 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."
Chimpanzees forcibly jabbed tools into hollow trunks or branches multiple
times and smelled and/or licked them upon extraction. Only two of the
22 reported cases were seen as playful - in the case of an infant male
- or exploratory in nature. In all other cases, chimps were judged by
the researchers to use such force in inserting the tool that prey within
the tree could have been injured. They witnessed just one case in which
a chimpanzee extracted a bushbaby - a smaller primate - through use of
the spear.
Despite the fact that hunting is predominantly an adult male chimpanzee
activity, only one adult male (of 11 males in the community) was observed
in the tool-assisted hunting. The reported incidents included one adult
female, one adult male, three adolescent females, two adolescent males,
one juvenile female, one juvenile male, and one infant male.
"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 authors conclude that these findings support a theory that females
might have played a role in the evolution of tool technology among the
earliest humans. Those technologies included hunting-related behavior,
in addition to 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," they wrote. "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."
In order to make their observations, Pruetz and her team spent four years
"habituating" the chimpanzees - familiarizing them with humans
- over their 63-square-kilometer Fongoli study site. That process has
changed over the years.
"You have to spend hours and hours attempting to follow them and
keeping up with them and basically getting them used to you so they think
you're just a benign presence," Pruetz said.
Pruetz and her Iowa State graduate students are continuing their chimpanzee
research in Senegal through additional National Geographic Society and
Iowa State grants. Stephanie Bogart, an Iowa State doctoral student in
ecology and evolutionary biology from West Palm Beach, Fla., is the project's
current site manager.
--Mike Ferlazzo, News Service
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Jill Pruetz
Around LAS
March 5-25, 2007
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