Chimpanzee the Hunter

When I talk about my time in the field, and how wonderful and fascinating chimpanzees are, one thing that often surprises people is that chimps eat meat. Listeners are truly shocked—"Wait what?" they say, "Chimps eat other animals?" They do, I say. They eat piglets, and small deer, but mostly monkeys. The chimps of Ngogo, Uganda, spend a good amount of time hunting monkeys—often opportunistically, when they encounter some while traveling—and eat their prey raw. It can be a grisly scene. Chimps everywhere tend to target a monkey called the red colobus. There are many other monkeys, and even another kind of colobus—the black-and-white colobus, very beautiful. But the reds are preferred, and the chimps of Ngogo have hunted them almost to extinction. The chimpanzees in the next territory over seem to do this less: Red colobus monkeys thrive over there.

I think many people imagine chimpanzees living peaceful lives in harmony with the natural world, causing no harm, free from the pressures and stresses of modern life—our simpler and better selves. The forest really is beautiful, with a wild freedom that is hard to describe once I’m back home in New York. And chimps do indeed spend many hours per day in peaceful harmony. They have very strong social bonds within their community and families, and form long-term individual bonds with specific others—what we humans would call friends. They spend many others, too, in dramatic aggression. Usually when chimpanzees are hunting meat, a group of them do it together, and there are elements that look a lot like strategy.

Natural Variations

Like us, much of chimpanzees’ behavior depends on their environment. How many are living together in their community? How large is their territory, or how tightly squeezed? What kinds of other animals and plants do they live with, and what is the weather like? Chimps that live near termite mounds will “fish” for those termites, using little stick tools they fashion. Termites don’t build mounds at Ngogo, so we don’t see that behavior there. There are a number of other chimp communities surrounding Ngogo, which means there are places for young females to move along to, when they hit puberty. And at Ngogo, this is the usual thing for females to do, to emigrate when they’re about 11. At other places where chimps have been closely observed—in Tanzania, for example—there are fewer emigration options, and it is more common for young females to stay put.

This is to say that there are likely reasons that red colobus are hunted so enthusiastically at Ngogo, and not elsewhere. Maybe red colobus were so plentiful at Ngogo that they were easier to find and catch, or maybe chimpanzees are so plentiful at Ngogo (and the group size is very large) that forming effective hunting parties was easier than elsewhere. That same large chimpanzee group size might also amplify the social-political benefit of meat-sharing, something we know chimpanzees make use of. Or maybe other aspects of Ngogo—like an unusual abundance of high-quality plant food—mean that chimps there have the time, energy, and nutritional resources to engage in risky things like hunting.

Hunting in the wild

One of the first times I saw meat-eating was after adult male Morton caught an infant monkey, having chased its mother until she dropped it in a panic. He killed it quickly and gave half to another male named Basie, who in turn let some drop down to his brother who sat below. One piece that made it to that brother, DJ, was the tiny skullcap, the top half of a white tennis ball. DJ tilted his head sideways and pierced it with his canine. I arrived to the scene after another hunt once, hurrying over from the next valley when I heard the commotion, just in time to see a powerful male tear off a piece for Cecilia—one of the rare females who participated in hunts herself. That particular prey was a black-and-white colobus monkey with a very long and beautiful tail—the tail was scooped up by a 4-year-old, who played with it for two days.

Morton had caught that monkey himself, but sometimes chimps take advantage of others’ hunts, too, to enjoy meat for free. Early in my time at Ngogo, me and my research partner found the chimpanzees Brownface and Damien early in the morning, having a lazy day: in five hours, they moved only twice. Brownface mostly sprawled on the ground, eyes half-shut, and Damien snacked quietly above on figs. Suddenly from the valley there was a wild, high-pitch screaming—Brownface lifted his head to listen but made no other move. My voice drifted across the clearing to ask A. if the screaming was cats; he shook his head no, baboons. Before I could form another question, Brownface leapt into a full tear through the forest—we sprinted after him, sweating, packs bouncing, clothes tearing on thorns, my compass on its string caught a branch and sliced the damp skin under my ear, and we lost him descending the steep valley side. In the mysterious way he has of predicting where they’re headed, A. changed direction and we angled, puffing, up the far slope. Brownface soon emerged 100 feet away, a small deer hanging limply from his mouth. The baboons had killed it and Brownface had stolen it. The two chimps settled in a tree, and we listened underneath to their grind and tear for the next three hours.

Why do it at all?

Chimpanzee are not what’s called “obligate” meat-eaters, like sharks or lions. That means they (like us) don’t need to eat meat, rather they do it if the opportunity arises. Meat eating can have both nutritional benefits and social ones. Unlike fruit, which grows in abundance with plenty for everyone, a freshly killed monkey is a coveted, finite resource that can be divided up for political gain. To reward an ally who had your back (or might, later), or endear you to a fertile female.

Humans can’t digest raw meat very well—our ancestors started cooking a long time ago, and we lost the ability—but chimps can, are highly motivated to eat it, and are skilled hunters. They are also intensely social, and can make good use of coordination and sharing—to an end that many people find uncomfortable and surprising. Food for thought.