The image of a chimpanzee hunting party is about as primal as it gets: Groups of brawny, violent males storming through the jungle, mercilessly attacking and mauling their prey. While that’s often the case, researchers conducting a study in Fongoli, Senegal, have painted an alternative picture: There, they found the only known instances of chimpanzees using tools to hunt vertebrate prey – and more often than not, it’s the females doing it.
“It’s just another example of diversity in chimp behavior that we keep finding the longer we study wild chimps,” said Jill Pruetz from Iowa State University. “It is more the exception than the rule that you’ll find some sort of different behavior, even though we’ve studied chimps extensively.”
Since 2007, Pruetz and her team have observed more than 300 tool-assisted hunts. While both males and females were observed using tools, 175 of those hunts were by females. The chimps were observed using short spears or prods while hunting bush babies, their primary source of protein in an otherwise barren area. While the spears aren’t used to kill the small primates, they injure or otherwise flush them out of hiding so the chimps can apprehend and kill them by hand.
Bush babies are smaller than the monkeys hunted by most chimpanzee populations, and are prone to hiding in nooks and crannies in tree hollows. The animals also happen to have very sharp teeth, and as such the chimps are reluctant to risk getting bitten. Often, males and females were seen working in concert: The female would flush the bush baby out of hiding with her stick, at which point the more opportunistic male could capture it. It’s believed that because females often have offspring in tow, it’s more difficult for them to chase down and dispatch prey animals.
This behavior has only been documented in this particular group of chimpanzees, which puzzles researchers a bit. Why did these chimps develop these techniques? One explanation is that because their prey is unique, they may have had extra incentive to develop a new skill. There’s also the question of why other populations haven’t learned how to use tools in this way. Pruetz says a different social atmosphere may have something to do with it.
“At Fongoli, when a female or low-ranking male captures something, they’re allowed to keep it and eat it. At other sites, the alpha male or other dominant male will come along and take the prey. So there’s little benefit of hunting for females, if another chimp is just going to take their prey item.”
This is not the first instance of chimpanzees being observed using tools in the wild. Famously, they’re known to use small sticks to “fish” for termites inside logs, though spearing a bush baby is obviously a different matter. Pruetz and her colleagues believe the Fongoli chimp behavior may give us insight into the very earliest days of hominid evolution.