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Chimps make an extra effort to warn their oblivious friends when deadly snakes are nearby

Chimps make an extra effort to warn their oblivious friends when deadly snakes are nearby


Dude, look out

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A chimp in Uganda’s Budongo Forest sees the fake snake.
A chimp in Uganda’s Budongo Forest sees the fake snake.
Video: Taï Chimpanzee Project

Chimpanzees live in dense forests filled with poisonous snakes and other threats — but luckily, they’ve got each other’s backs.

New research shows that when chimpanzees see a poisonous snake, they make an extra effort to alert other chimps that are unaware of the danger by making alarm calls and pointing out the location of the snake by gazing at it. That suggests that chimps communicate — and cooperate — with each other in more complex ways than previously thought possible.

Previous studies have shown that chimps warn others of danger, and are more likely to stop making alarm calls after the other chimps have climbed to safety. But today’s study, published in Science Advances, goes an extra step: it shows that chimps change their behavior — and adapt their alarm calls — based on whether the other chimps are aware of the danger. In other words, chimps take other animals’ perspective into account when communicating. And that’s pretty much what people do: when we talk, we consider what information is available to others.

“There seems to be more going on in chimpanzee communication — and possibly in other animal communication, especially the vocalization part — than has been assumed possible before,” says study co-author Catherine Crockford, a researcher at the Max Planck Institute for Evolutionary Anthropology.

“They were convincing enough to scare our field assistants.”

Crockford got the idea for her research while spending hours in Uganda’s Budongo Forest, and observing chimps alerting each other of poisonous snakes. First, she and her team created fake snakes out of chicken wire and plaster that resembled deadly gaboon and rhinoceros vipers. “They were convincing enough to scare our field assistants,” she says. The researchers then placed the fake snakes where chimpanzees were expected to pass by, setting up a video camera to record their reactions. One-third of the animals were observed alarm calling other chimps in their group; then they indicated the snake’s position by gazing back and forth from the snake to the other chimps, continuing to do this until the others had seen the snake.

In a second experiment, the researchers also played prerecorded calls — either an alarm hoo or a rest hoo. The two calls influenced how the chimps reacted: those that had heard the rest call a few seconds before coming across the fake snake — which suggested that a nearby group member was unaware of the snake — gave more warnings, making more alarm calls and using body language. The findings suggest that when a chimp thinks its fellows don’t know about the danger, the chimp will make an extra effort to make sure they’re informed. In other words, its vocalizations seem to change based on what the other chimps know or don’t know.

“They really have these strong friendships.”

The findings add to our understanding of how animals communicate with each other. They also tell us a bit about human evolution: it suggests that relatively complex forms of communication may have emerged before humans developed a language. “I think it helps us learn much more about ourselves, how our brains work,” Crockford says. And perhaps even more about how we interact with each other.

The chimps in the study were found to give more warnings about the snake if the other chimps were friends or kins. “They really have these strong friendships,” Crockford says. These friendships help individuals thrive: chimps and other primates who are more socially connected are found to have more offspring, Crockford says. “The motivation to keep friends [safe], to stop them being taken away by others, probably occupies quite a lot of their day and their brain work,” she says. “It’s a really crucial part of survival.”