Sarah Knapton
Thu, 2 November 2023
Researchers spent three years following two neighbouring chimpanzee groups in the West African forests of Côte d'Ivoire - University of Cambridge
It might be considered the original example of “gorilla” warfare.
Chimpanzees have been spotted using hilltops to conduct reconnaissance missions before invading enemy territory.
The tactic was thought to be uniquely human, demonstrating a sophisticated level of intelligence and understanding about the importance of vantage points.
But researchers at the University of Cambridge say it is now clear that one of the oldest military strategies exists in our closest relatives.
“Tactical warfare is considered a driver of human evolution,” said Dr Sylvain Lemoine, a biological anthropologist from Cambridge’s Department of Archaeology.
“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.”
Dr Lemoine says chimpanzee behaviour requires complex cognitive abilities that help to defend or expand their territories - University of Cambridge
Researchers spent three years following two neighbouring chimpanzee groups in the West African forests of Côte d’Ivoire, and found they were often involved in skirmishes on the no-man’s-land between the borders of their territories.
The groups consisted of around 30 to 40 chimpanzees, who were found to protect their turf with regular border patrols around the periphery.
But their behaviour changed when they were considering entering the contested frontier zone.
In advance of a dangerous incursion, the chimpanzees would climb hills and grow quiet in their eating and foraging so they could pick up the sound of neighbouring groups.
When it was clear that the enemy chimps were far away, the group was more likely to descend the hill and enter the disputed zone.
Experts said it suggests that chimpanzees on high ground use sounds to gauge the distance of rivals, and decide whether to make an incursion, or avoid a costly fight.
The animals make excitable vocalisations to communicate with group members or assert their territory - iStockphoto
“These aren’t so much lookout points as listen-out points,” added Dr Lemoine.
“Chimpanzees drum on tree trunks and make excitable vocalisations called pant-hoots to communicate with group members or assert their territory. These sounds can be heard over a kilometre away, even in dense forest.”
She added: “It may be that chimpanzees climb hilltops near the edge of their territory when they have yet to hear signs of rival groups. Resting quietly on an elevated rock formation is an ideal condition for the auditory detection of distant adversaries.”
Chimpanzees often try to expand their territory by sending raiding parties into enemy zones to gradually establish a presence when the other group is elsewhere.
More territory means more access to food and even better mating chances, but fights and even kidnappings are always a risk during a land grab, so a hilltop recce can help avoid a lethal confrontation.
Ahead of a dangerous incursion, the chimps would climb hills and grow quiet in their eating and foraging so they could pick up the sound of neighbouring groups - University of Cambridge
The team found that chimpanzees stopped on peripheral hills 58 per cent of the time when heading towards the disputed border region, but only 25 per cent of the time when moving back towards their territory.
Following a hilltop mission, the likelihood of advancing into enemy territory increased from 40 per cent when rivals were 500 metres away, to 50 per cent when rivals were at 1,000m, to 60 per cent when rivals were at 3,000m.
The type of hills near the border used for reconnaissance are known as “inselbergs”, isolated rocky outcrops that break up the forest canopy.
Other mammal species such as meerkats use high ground to keep watch for predators or call to mates but Cambridge researchers say the new study is the first to show an animal other than humans employing strategic use of elevation to assess potential conflict.
The research was published in the journal Plos Biology.
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