Chimpanzees don’t only forage for fruit; from time to time they also seek out opportunities to acquire protein-rich meat.

To catch their agile monkey prey in the canopy, chimpanzees are better off having companions hunting alongside them. And to be especially successful, new research published this week in Science Advances indicates that communication is key. Chimpanzees hunting in the tree canopy. Photo by Ian Gilby/ASU

Similar to humans, chimpanzees use communication to coordinate their cooperative behavior — like during hunting. When chimpanzees produce a specific vocalization, known as the “hunting bark,” they recruit more group members to the hunt and capture their prey more effectively.

Hunting barks make the chase more effective

By studying more than 300 hunting events recorded over the last 25 years at the Kanyawara chimpanzee community in Uganda, researchers — including ASU primatologist Ian Gilby — have discovered that by making bark vocalizations, the wild apes catalyze group hunting, rendering this form of cooperative behavior more effective.

Gilby is a research associate with the Institute of Human Origins and associate professor in the School of Human Evolution and Social Change. Gilby is also the director of the Jane Goodall Institute Research Archive and Database at ASU. 

Scientists have been debating for years whether hunting in chimpanzees involves any real coordination between hunters or whether each individual simply chases their own prey independently. This new research shows that hunts featuring the occurrence of specific hunting calls play out very differently from hunts where this signal is not produced.

“Strikingly, following the production of hunting barks, we observed more hunters joining, greater speed in beginning the chase and a shorter time to make the first capture,” says study author Zarin Machanda of Tufts University, who heads up the Kanyawara Chimpanzee Project.

“Chimps who produce hunting barks inform those nearby about their motivation to hunt, and this information may persuade reluctant individuals to join, boosting the overall chances of success,” said Joseph Mine, a PhD student at the University of Zurich who led the study.

“However,” cautions Gilby, who is an expert on chimpanzee hunting behavior, “purely observational studies like these can only give us hints about what is happening in the minds of these apes. Rather than serving to coordinate a complex, cooperative act, these barks may simply advertise that a particular chimpanzee has decided to hunt, which in turn, increases the potential success rate of other hunters, even if they don’t actively work together.

"The more hunters there are, the greater the likelihood that hunters acting in their own self-interest will make a kill.”

Co-evolution of communication and cooperation

The evolutionary biologists considered a wide array of other factors that may affect the outcome of a hunt, including the presence of skilled hunters or potential distractions, but the occurrence of hunting barks retained a key role.

“We can see from the multitude of hunting events that sometimes the chimps are just not interested in hunting as a team. But when they are especially motivated, they communicate with their group members and engage in the hunt collectively,” says Simon Townsend, a researcher at the University of Zurich who helped lead the study.

The findings offer new insights into the evolution of the amazingly complex form of communication that we see in humans today: language. It is widely accepted that communication and cooperation are tightly linked and co-evolved in humans. Over time, as one became more complex, so did the other, generating a feedback cycle that ultimately led to language. 

Evolutionary roots at least 7 million years old

However, it remains unknown how far back into humans’ evolutionary past this relationship can be traced.

The research group believes the results indicate that the relationship between vocal communication and group-level cooperation is ancient and that the link seems to have been in place for at least 7 million years — since the last common ancestor with chimpanzees.

"Vocal signals facilitate cooperative hunting by wild chimpanzees" published in Science Advances. Joseph G Mine, Katie E Slocombe, Erik P Willems, Ian C Gilby, Miranda Yu, Melissa Emery Thompson, Martin N Muller, Richard W Wrangham, Simon W Townsend, Zarin P Machanda. July 29, 2022. DOI: 10.1126/sciadv.abo5553