One of the male chimpanzees tracked for the study (Credit: Roman M. Wittig/Tai Chimpanzee Project)

Humans and chimpanzees share 98.8 percent of their DNA, so it's not surprising that they display similar behaviors and traits. They include communicating through gestures and vocalizations, and using tools to complete tasks. Now, new research reveals that chimpanzees employ human-like military tactics to evaluate risk and expand their territories.

For their study, Dr. Sylvain Lemoine and his team at the University of Cambridge observed the behavior of two western chimpanzee groups at West Africa's Tai National Park. The researchers used GPS trackers to follow the chimps for 8 to 12 hours daily from 2013 to 2016. They found that both groups regularly patrolled the edges of their territories. Like humans, they formed small groups and moved closely in a coordinated manner. The chimps also seemed to seek out higher ground along the borders. While on these hills, they sat quietly listening for sounds from their rivals.

The Tai National Park chimpanzees attentively listen for sound from rival chimpanzees (Credit: Roman M. Wittig/Tai Chimpanzee Project)

The border between chimp communities is not set in stone. Their daily presence in an area is what matters. Hence, when there was a low risk of conflict, such as fewer rivals, the patrolling chimpanzees felt more confident to enter and take over part of their neighbor's territory.

"They use the high spots to find the right conditions where they can take the risk — or not — of attacking," Dr. Lemoine said.

The scientists state that many animals climb to higher ground to keep watch for predators. However, chimpanzees are the first animals, other than humans, to strategically use elevation to assess the risks of a conflict with another group.

The chimpanzees leaving a hilltop after listening for their rivals (Credit: Roman M. Wittig/Tai Chimpanzee Project)

"Tactical warfare is considered a driver of human evolution," said Dr. Lemoine. "This chimpanzee behavior requires complex cognitive abilities that help to defend or expand their territories."

The scientists revealed their findings in the journal PLOS Biology on November 2, 2023. Though they only studied West African chimpanzees, the team believes that other chimps probably use similar tactics to take control of each other's territory.