An ISU researcher made an amazing discovery about chimpanzees while studying them in Senegal, Africa.

Chimpanzees have been discovered using sharpened sticks to hunt for bush babies, nocturnal animals that hide in tree branches during the day. Researcher Jill Pruetz, assistant professor in anthropology, has observed several cases of chimps poking sticks into openings in tree branches and one case of a chimp successfully skewering a bush baby.

“Once we started following them, then we observed this particular behavior and it was probably the most exciting thing I’ve seen so far at the site,” Pruetz said.

Brent Danielson, associate professor in ecology, evolution and organismal biology, studies small mammals, and said his first impressions were ones of amazement.

“These chimps are using spears and even making spears and going to the extremes of even sharpening [the spears] and that seems, to me, incredible,” Danielson said. “There are not that many animals that make tools in the world, however liberally we define tool-making.”

The chimpanzees bite the sides of the sticks to sharpen them and use the sticks as spears to attempt to incapacitate bush babies. Pruetz said the weapons are needed because once a bush baby has been roused, it can leap away into the trees and avoid capture.

“What we saw with the chimps at my site were that they were actually, for all intents and purposes, trying to disable the bush babies,” Pruetz said. “They were taking these tools and modifying them and then using them to stab into the holes. In some cases they would even modify the tip of the tool, so they were making a sharp tool.”

Although there is only one documented instance of a chimpanzee actually catching a bush baby with a tool, Pruetz said she believes the behavior is actually hunting.

“They use a tool, they pound it in there, they smell it, lick it and then they’ll pound it in there some more. This, to me, is reasonable evidence that they are trying to incapacitate the bush baby because they could break off the limb and just try to grab it,” Pruetz said.

The behavior is also interesting because it is mostly observed in females and younger males instead of in the adult males, the typical hunters. Pruetz said it was a way for the females and younger males to be able to compete for food with the males.

“It would seem like suddenly they have the ability to secure quite a bit more [meat],” Danielson said.

The climate might be the root of this behavior, Pruetz said. Chimps at other sites have been known to eat red colobus monkeys, which do not live at the site because of the heat. The chimps then have to find alternatives for their diet.

“We haven’t studied chimps in this habitat before, so this is a really dry habitat and not a very chimpy habitat,” said Pruetz.

The climate is probably also the source of a few other unique behaviors in the Senegal chimps, such as the attraction to water.

“One other thing that the chimps exhibit at this site is what appears to be sort of a love of water,” Pruetz said.

“Once the rains start in May, the adult males will actually have dominance interactions – they will assert their dominance over the right to soak in these pools of water.”

Pruetz said the chimps also use caves to stay cool during the day in the dry season, another behavior not seen in other groups of chimps.

Pruetz plans to go back to the site in Senegal in May.