Members of a troop of chimpanzees living at a site called Fongoli in southeastern Senegal have been observed by scientists fashioning tree branches into spears and using them to hunt and kill bushbabies. The researchers, a combined team with members from the U.S. the U.K. and Germany have published their observations and findings in Royal Society Open Science.
In their seven year study of the chimps living at the site, the researchers spotted chimpanzees breaking off tree branches, tearing off smaller branches and leaves, removing the weak tips and sometimes gnawing on the ends to sharpen them. The spears (which were on average about 75 centimeters long) were then used to stab bushbabies sleeping in their nests in tree hollows. The poking, the team reports was not lethal, instead, it caused injuries to the bushbabies which was enough to allow the chimps to bite and kill them with relative ease.
Bushbabies are small primates with big eyes and sharp teeth, and serve as a primary protein source for the chimps living in that part of Africa, where other sources are rare. The researchers began their study in 2007, observing chimp behavior up until last year. During that time period they recorded 308 spear hunting events, which they noted, was more common for females than males—they accounted for 61 percent of the total. The researchers suggest this is likely the case because it is more difficult for females to chase down prey because they almost always have offspring clinging to their bodies. To date, the chimps are the only known animal to use a tool as a weapon to hunt a “large” animal, other than humans—chimps in other troops have been seen to use twigs as tools to help collect termites, but scientists do not count that as hunting.
The researchers also found that the troop at Fongoli was a much more cooperative collective than has been found in chimp troops in other parts of Africa—dominant males, for example, allow females and smaller males to keep and eat what they kill, rather than stealing it from them. That might help explain the development of tool use, which the team speculates, likely began with females. They also suggest the same might be said for early humans, who developed weapons use in a very similar environment.