Western chimpanzee (Pan troglodytes verus) spear hunting

One popular and enduring image of the human past is that of a lone hunter, spear in hand, standing up to a mammoth or other fearsome beast. This is not just imagination either, as we have direct evidence for wooden spears dating back some 300,000 years in Germany (where they were likely wielded by our Neanderthal-like relatives), while some of the oldest known cave art—from Sulawesi over 40,000 years ago—appears to show spear-hunting of a small water-buffalo.

All of which made the summers of 2005 and 2006 rather unusual. Jill Pruetz of Iowa State University had been habituating the wild chimpanzees of Fongoli, in southeastern Senegal, since 2001. Habituation is a slow process, during which wild animals gradually become familiar with researchers watching them from a distance, allowing their natural behaviour to be observed.

In 2006 the Fongoli community was made up of 15 female and 20 male chimpanzees, from infants to adults. As they ranged widely across the area’s grasslands and woodlands, the researchers began noting a particular behaviour around hollow trees.

Chimpanzees—both males and females—would carefully explore cavities within the trees. They would then break off a nearby branch, stripping back the twigs and leaves to leave a long, thin ‘spear’. Sometimes this tool-making process even included narrowing the branch tip into a point using their teeth. Returning to the cavity, the chimpanzee would then repeatedly and forcefully drive the branch into the hollow, occasionally pausing to withdraw and sniff the end of the tool.

Their target? The galago (Galago senegalensis)—a small fellow primate with large, nocturnal eyes and ears. This distinct appearance and size has earned them the common name of bushbaby, and they reach only a few hundred grams when fully grown. During the day, galagos hide while they sleep, with tree cavities offering excellent protection.

Capture

Not all spearing attempts resulted in a tasty bushbaby snack. In fact, most did not. But the behaviour was so widespread among this community that it was clearly not a random event. By the time of a follow-up report in 2015, Pruetz and her colleagues had amassed data on over 300 cases of tool-assisted hunting at Fongoli.

Almost all of these hunts took place around or during the June-September wet season at the site. Only a few chimpanzees over two years of age didn't at least try spear-hunting, although they weren’t successful in actually capturing a galago until they passed age 7 (at which point they are considered ‘adolescents’).

The age difference matters. While adult females and males successfully captured a galago after spearing it around a fifth of the time, adolescents achieved that goal fewer than one in twenty times. And females hunt more often with tools than the males.

All chimpanzee communities capture mammalian prey and share meat, although it is a minority of their overall diet. Across Africa, however, only the Fongoli chimpanzees are currently known to hunt with hand-held tools. And at Fongoli this quirk is reserved for bushbabies—other prey such as vervets, baboons, monkeys and mongoose are eaten there, but those are chased down and caught directly by hand.

It isn’t clear whether galagos are usually stunned, incapacitated or killed by the spearing chimpanzees. Good practice at field sites dictates keeping a safe distance away from the animals, to avoid unintentional transmission of disease from human to chimpanzee, or stressing an animal who would need to monitor whether an encroaching observer is a threat. As a result, a bushbaby’s condition can be difficult to accurately gauge when it is hauled from a cavity, but the animals (the chimpanzees, if not the galagos) are safer and healthier.

What we do know is that the bias towards female tool-use in hunting at Fongoli deserves closer attention. When we picture that lone human hunter armed with a spear, deep in human prehistory, how often do we automatically imagine them as male?

Meat is an important resource for chimpanzees—given a choice vertebrate meat is often preferred over other food types—and the Fongoli bushbabies offer an opportunity for female hunters to get in on the feast. At other sites, the larger, dominant male chimpanzees have received greater attention from researchers as the controllers of meat capture and sharing. Pruetz and her colleagues suggest that the more open, savannah-like environment at Fongoli means that focusing on the enclosed bushbabies (with attendant tool-use) raises the chances of a female hunter catching and then eating meat.

To the extent that chimpanzees are used as stand-ins for human evolution, therefore, we would do well to consider that image of the male hunter as no more than a hypothesis. Like all hypotheses, it needs evidence, and an awareness of the male-dominated academic and science communication worlds from which it originated, if it is to be properly assessed. Spear-hunting is as much about intelligence and preparedness as it is about standing up to a rogue mammoth.

Coda: is this hunting?

You may be wondering whether spearing a sleeping galago in its cavity is actually hunting per se. Rest assured that the scientists did not apply that label lightly, and ultimately they decided that:

we consider this hunting because the prey is mobile rather than sedentary, the prey can be aggressive, and regardless of size, Fongoli chimpanzees show aversion to being bitten by a Galago.

In fact, the Fongoli chimpanzee spear hunt is arguably much more worthy of the term ‘hunting’ than a modern human with a long-range rifle killing a lion or deer. There is danger, the prey can (and does) escape, and it requires skills that take years to develop. Only a human-centred bias would deny that the chimpanzee hunt, therefore, and removing those biases is the first step towards meaningful understanding of the natural world.

Further viewing: Here’s a short video from National Geographic of one of the first Fongoli hunts, narrated by Jill Pruetz:

Sources: Schoch, W. et al. (2015) New insights on the wooden weapons from the Paleolithic site of Schoningen. Journal of Human Evolution 89: 214-225. || Aubert, M. et al. (2019) Earliest hunting scene in prehistoric art. Nature 576: 442–445. || Pruetz, J. & P. Bertolani (2007) Savanna Chimpanzees, Pan troglodytes verus, Hunt with Tools. Current Biology 17: 412–417. || Pruetz, J. et al. (2015) New evidence on the tool-assisted hunting exhibited by chimpanzees (Pan troglodytes verus) in a savannah habitat at Fongoli, Sénégal. Royal Society Open Science 2: 140507. || National Geographic (2007) Chimps Use Tools to Hunt Mammals. https://video.nationalgeographic.com/video/00000144-0a1e-d3cb-a96c-7b1f94080000.

Main image credit: Pruetz et al. 2015 doi: 10.1098/rsos.140507