Chimpanzees use high ground to gather information about rival groups and reduce the risk of confrontation, a study suggests.
Until now, using elevated terrain to observe other groups was seen as a tactic unique to humans, and often deployed in warfare.
But a three-year-long study has shown that when chimpanzees approached the outskirts of a rival group’s territory, they were more than twice as likely to climb hills than when they were travelling towards their own territory.
And when on a hilltop, these primates were more likely to spend time resting and refrain from eating noisily – allowing them to hear the distant sounds made by their rivals, according to researchers.
After descending from a hill, the chimpanzees tended follow a course of action that would reduce the risk of encountering their rivals.
While other mammal species such as meerkats use high ground to keep watch for predators or call to mates, researchers said this is the first time an animal other than humans has been found to use elevation to monitor enemies.
Dr Sylvain Lemoine, a biological anthropologist from the University of Cambridge’s Department of Archaeology, said: “Tactical warfare is considered a driver of human evolution.
“This chimpanzee behaviour requires complex cognitive abilities that help to defend or expand their territories, and would be favoured by natural selection.
“Exploiting the landscape for territorial control is deeply rooted in our evolutionary history.
“In this use of war-like strategy by chimpanzees we are perhaps seeing traces of the small-scale proto-warfare that probably existed in prehistoric hunter-gatherer populations.”
For the study, the researchers monitored the movements of chimpanzee groups at the Tai National Park in Cote d’Ivoire using GPS trackers.
Using the data from the trackers, the scientists were able to create maps of two chimpanzee territories that border each other.
Dr Lemoine said: “To establish and protect their territory, chimpanzees perform regular tours of the periphery that form a sort of ‘border patrol’.
“Patrols are often conducted in subgroups that stay close and limit noise.”
Analysis showed that following their hilltop stint, the chimpanzees were 40% more likely to advance into enemy territory when rivals were 500 metres away, 50% more likely when rivals were 1000m away, and 60% more likely when rivals were 3000m away.
While the study suggests that chimpanzees use hilltop observations to avoid confrontation, the researchers also found that fights – and even kidnappings – occasionally occurred between rival group members.
Dr Lemoine said: “Occasionally, raiding parties of two or three males venture deep into enemy territory, which can lead to fighting.
“Confrontations between rival chimpanzees are extremely noisy.
“The animals go into an intimidating frenzy, screaming and defecating and gripping each other’s genitals.”
The research is published in the journal Plos Biology.