Why Do Chimpanzees Throw Their Feces?

Like the primate version of Nolan Ryans, chimpanzees have earned a reputation for their surprising throwing skills. But unlike baseballs, it's not a ball they're throwing. These primates often engage in an unsettling behavior, hurling their own feces at unsuspecting bystanders, much like relief pitchers at the end of a tight game. It's another reason why they don’t make ideal pets.

What’s the reason behind this behavior? Could this act of tossing poop actually be an indicator of intelligence?

According to the Jane Goodall Institute of Canada, this behavior is rarely observed in wild chimpanzees that roam freely. While they do throw objects to express frustration, it's typically rocks or sticks. In captivity, however, the lack of available materials forces frustrated or stressed chimps to resort to what’s most abundant: their own poop.

A chimpanzee doesn’t throw feces just because it's easy to access. In captivity, poop-throwing often triggers a reaction, whether from zoo workers or visitors. The chimp learns to associate the action of throwing waste with a response, typically surprise or shock. While this behavior isn’t exclusive to chimps—howler monkeys in Belize also engage in it—chimpanzees are perhaps the most notorious for it. By tossing their feces, chimps discover that they can influence the behavior of others. Throwing a poop projectile usually makes people scatter.

While one might quickly link poop-throwing with low intelligence, the reality could be the opposite. A 2012 study published in Philosophical Transactions of the Royal Society B revealed that chimpanzees who displayed accuracy in their throws had enhanced development in their motor cortex, the part of the brain responsible for coordinating physical actions. These chimps also showed better communication between the motor cortex and Broca’s area, which helps process language in humans. Notably, the left hemispheres of their brains, which control right-hand movements, showed greater development. The chimps with rocket-like aim also turned out to be better communicators within their social groups.

Another sign that poop-tossing might be a sign of intelligence: it may be planned. A 2009 article in Current Biology documented a chimp named Santino, from Furuvik Zoo in Sweden, who displayed real strategic thinking. Santino was known for his aggression (he later killed another male chimp) and for throwing rocks at visitors watching him behind a fence. Zookeepers found that Santino had been gathering rocks from the moat that separated him from the visitors. He did this before the zoo opened, ensuring he had plenty of projectiles. He even broke apart large concrete rocks to create dinner plate-sized missiles. Other chimps have been seen to gather poop in their hands, waiting for an annoying human to walk by.

Chimps can be irritable for many reasons. In the wild, it might be due to interactions with other primates. In captivity, they may grow frustrated by the constant attention of onlookers and the limitations on their movements. If you're observing chimps in a zoo, keep in mind that they might become irritated. And depending on how accurate their aim is, you could feel the consequences.