Tracking Senegal’s famous hunting chimps


The world took notice in 2007 when Iowa State University anthropologist Jill Pruetz announced the discovery of African chimpanzees that use sharpened sticks to hunt smaller animals—an activity previously deemed exclusive to humans. But exactly how the chimps make and use their tools of death was less certain until UIndy student Trisha DeWitt showed up.

After a month of preparation in Costa Rica, six weeks in Senegal’s 100-degree-plus temperatures, and further research back on the UIndy campus, DeWitt found some answers. On a thesis project (DeWitt recently completed her master’s degree in human biology), advised by Professor Christopher Schmidt, she spent 160 hours observing, photographing, and shooting rare video of the tool-making chimps at the Iowa State professor’s National Geographic-supported research and conservation site in the savannas of western Africa.

DeWitt noted, among other things, that chimps of all ages in the small community make their tools quite methodically, breaking off live branches of a certain length, then stripping and sharpening the sticks by running them side-to-side through their teeth, in a motion similar to that used by violinists. On the hunt, she says, a chimp will forcefully drive the pointed end into a tree cavity in hopes of striking some prey—most likely an adorable bush baby—then pull the tool out to sniff or lick for clues.

“They don’t use the tool to kill the bush baby,” DeWitt says. “They only use it to detect if it’s there or to immobilize it.”

To complete the project, she also collected several teeth from deceased chimps for analysis using the UIndy Department of Anthropology’s white-light confocal imaging profiler, a high-tech microscope that her adviser, Schmidt, obtained with a grant from the National Science Foundation. Electronically viewing the tooth surfaces at high magnification, she found not only the vertical etching that occurs from eating, but also deep horizontal grooves on the rear side of the incisors, suggesting that the chimps use their very front teeth, not their molars or premolars, to shape the sticks. The findings could suggest new approaches to the study of early human development.

“This is very preliminary,” says DeWitt, who grew up in southern Indiana. “I’m building a basis for future research that can bridge the gap between primatology and dental microwear studies.”

DeWitt, who plans to pursue a doctoral degree, now works for ACL Laboratories in the Chicago area, processing medical specimens. She has submitted her thesis work for publication in Folia Primatologica, the official journal of the European Federation for Primatology.