Chimpanzees Discovered Making And Using Spears To Hunt Other Primates

Though I just found this but it was published by Science Daily on the 23rd of Feb

Science Daily — Chimpanzees in Senegal are regularly making and using spears to hunt other primates -- without human assistance -- according to research led by an Iowa State University anthropologist. That study, funded by the National Geographic Society, is the first to report habitual tool use by non-humans while hunting other vertebrates.


Tia, who Professor Pruetz reports is an adolescent female chimp who displayed the tool-use hunting behavior frequently. The photo is by Maja Gaspersic, a former grad student from Slovenia who was a past project manager at the Fongoli site. (Credit: Maja Gaspersic / Courtesy of Iowa State University)Ads by Google Advertise on this site

ISU Assistant Professor of Anthropology Jill Pruetz and Paco Bertolani -- a graduate student with the Leverhulme Centre for Human Evolutionary Studies, Department of Biological Anthropology 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." The article will be available online in the professional journal on Thursday, Feb. 22.

"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.

Females lead tool-assisted hunting

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."

They 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."

Four years spent habituating chimps

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. "What researchers used to do once upon a time was to feed the chimps bananas, which got them used to humans very quickly. But this method causes problems. We know nowadays that there are a lot of diseases that can be passed from chimps to people and visa-versa. There are also ethical problems because the chimps at some sites got over-habituated to where they weren't fearful of humans and could cause harm to people."

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 ISU doctoral student in ecology and evolutionary biology from West Palm Beach, Fla., is the project's current site manager.

The research during the study period was supported by grants from the National Geographic Society, Center for the Study of Violence at Iowa State University, ISU Foreign Travel Grant, ISU Faculty Professional Development Grant, and the American Society of Primatologists Conservation Grant.

Note: This story has been adapted from a news release issued by Iowa State University.

Chimps Have Been Found Using Caves For Shelter


Science Daily — Chimpanzees in Senegal apparently have much in common with our earliest human ancestors.

This photo by ISU anthropologist Jill Pruetz shows the view from inside the cave in Senegal where she found evidence of chimpanzee use. (Credit: Image courtesy of Iowa State University)

A month after Iowa State University Assistant Professor of Anthropology Jill Pruetz reported chimpanzees at her Fongoli research site are using spear-shaped tools to hunt, her new study indicates those same chimps are also seeking shelter in caves to get out of the extreme African heat. The National Geographic Society-funded research is the first to document regular chimpanzee cave use.

Pruetz' paper, titled "Evidence of Cave Use by Savanna Chimpanzees (Pan troglodytes verus) at Fongoli, Senegal: Implications for Behavioral Thermoregulation," will be published in an upcoming issue of Primates, a professional journal.

The paper reports that the chimpanzees' cave use was based primarily on indirect evidence -- feeding traces, feces and hairs -- gathered from one cave from January through December 2004. Supplemental data from observational records was also collected from May 2001 through March 2006. Pruetz has also witnessed the chimps entering and exiting the cave.

"I talked about it (chimps using caves) at a meeting in Japan several years ago. I just kind of reported it and everyone was amazed," she said. "They thought it was great and nobody had ever heard anything like it, except that Jane Goodall actually came up to me after the talk and she said that she heard an incident in Mali where someone was doing a chimp survey and they surprised a bunch of chimps coming out of a cave. But that's the only other instance that anyone, as far as I know, has ever heard of it."

Chimps use caves to avoid African heat

In the paper, Pruetz concludes that the chimps' cave use is a response to heat at her Fongoli research site. She collected data on temperatures within Sakoto cave -- the largest cave within her site -- as well as the different habitats used by chimpanzees, such as gallery forest and woodland.

Her research found that chimps primarily use Sakoto cave as shelter during the hottest and driest times of the year, from October through May. The cave is several meters deep and located at the head of a shallow ravine, which was formed through water runoff from a plateau. Between 2001 and 2004, average annual daily temperature within the Sakoto cave was 24.2 degrees Celsius, compared with 29.6 degrees in the woodland habitat and 24.6 in grassland habitat -- both located approximately 30 meters from the cave and at the edge of the Sakoto ravine. Pruetz attributes the lower grassland temperature to wind. In the Sakoto gallery forest habitat approximately 20 meters from the cave, temperatures averaged 26.4 degrees Celsius.

"It seems very much cooler when you go into the cave, but I wanted to make sure I took temperature measurements in the cave and different habitats," said Pruetz. "It is significantly cooler in the cave and the only time they (chimps) use the cave is during the dry season when you have the hottest temperatures outside.

"They're (chimps) just using it as a way to avoid the heat," she said. "They just lie in there and rest. They'll bring food in and eat it in there, and groom. They sort of just hang out and relax."

Maximum temperatures produce primate heat stress

Pruetz wrote in the article that maximum temperatures may be a more important measure of heat stress to primates than average temperatures. And that stress may be what's driving the chimps into the caves, although the explanation may not be that simple.

"While cave use by Fongoli chimpanzees appears to correlate with temperature, a number of factors probably work in association to influence this behavior, underscoring the complexity of the relationship between climate, habitat, and the behavior of hominoids inhabiting a dry, open environment," she wrote.

But maybe it shouldn't be so surprising that chimpanzees are using caves after all.

"It shouldn't be surprising that chimps are using caves," said Pruetz. "If you look at the scientific name of the chimps, the species name is troglodytes, which means cave-dwelling."

Pruetz will return to Senegal in May. She and her Iowa State graduate students plan to measure relative humidity in the different habitats used in this research.

The study was supported by grants from the National Geographic Society, National Science Foundation, Leakey Foundation, U.S. Fish and Wildlife Great Ape Conservation Grant, Primate Conservation Inc., and Iowa State University.

Note: This story has been adapted from a news release issued by Iowa State University.