Chimpanzees seek high ground to spy on rivals during warfare

In a study that could reshape our understanding of strategic behavior in non-human animals, researchers have found that chimpanzees in Côte d’Ivoire’s forests utilize high ground to scope out rival groups, echoing one of the oldest human military tactics. 

Complex cognitive abilities 

This research details the remarkable findings from the Taï Chimpanzee Project, shedding light on the complex cognitive abilities of these primates. The project is currently led by study senior author Dr. Roman Wittig from CNRS in France.

Study lead author Dr. Sylvain Lemoine is a biological anthropologist in the Department of Archaeology at the University of Cambridge. He emphasized the significance of this discovery.

“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, and would be favored 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.”

How the research was conducted 

For up to 12 hours per day, teams of researchers followed four groups of chimpanzees that are “habituated” to the presence of humans. Each group consisted of 30-40 adult chimpanzees at any one time. 

Over three years, the researchers meticulously tracked the neighboring chimp groups, accumulating over 21,000 hours of data. 

What the researchers learned 

To establish and protect their territory, chimpanzees performed regular tours of the periphery that form a sort of “border patrol,” explained Lemoine. “Patrols are often conducted in subgroups that stay close and limit noise. As an observer, you get a sense that patrolling has begun. They move and stop at the same time, a bit like a hunt.”

The experts found that chimps were more inclined to climb hills – isolated rocky outcrops known as “inselbergs” – when approaching the border area of their territories, which are often sites of conflicts. 

Significantly, they were twice as likely to do so compared to other times, indicating a deliberate strategic choice rather than random movement.

Chimpanzee territory listening posts

In these elevated areas, the chimps behaved differently. They would remain silent, refraining from foraging or making noise, likely to better detect the sounds of the distant rival groups. 

“These aren’t so much lookout points as listen-out points,” said Lemoine. “Chimpanzees drum on tree trunks and make excitable vocalizations called pant-hoots to communicate with group members or assert their territory. These sounds can be heard over a kilometer away, even in dense forest.”

“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.”

Tactical decisions in chimpanzee territory

The researchers used GPS trackers to map out the chimpanzee territories, aligning their findings with historical maps for accuracy. 

“Chimpanzees often expand their territory by encroaching and patrolling in that of their neighbors. Hilltop information-gathering will help them to do this while reducing risks of encountering any enemies,” said Lemoine. “The border zone between the two groups was in a state of flux.”  

Upon descending from these vantage points, the likelihood of chimps advancing into enemy territory increased significantly with the distance of the rival group, indicating that the high ground reconnaissance served to inform their tactical decisions.

Avoiding confrontation

But why are the chimps taking these risks? More territory can boost food provision and mating chances, explained Lemoine. His previous work suggests that larger chimpanzee groups live in bigger territories with reduced pressure from rivals, which in turn increases birth rates within communities.

The latest research suggests that chimpanzees use hilltop reconnaissance to avoid confrontation, and violence is relatively rare, said Lemoine. However, fights, and even killings, did occur between rival group members.

“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.”

More about chimpanzee territory

Chimpanzee territories are a fascinating subject, as they reflect the complex social structures and behaviors of one of our closest living relatives. 

These territories are areas that are actively defended by a community against intrusion by other groups, and they hold a critical importance in the lives of chimpanzees.

Size and boundaries

Chimpanzee territories can vary greatly in size, depending on the abundance of resources and the number of individuals in a group. They can range from about 5 to over 35 square kilometers. 

The boundaries of these territories are not fixed lines but rather zones of overlap where tensions and conflicts can occur.

Resource distribution in chimpanzee territory

The territories are rich in resources such as food (including fruits, nuts, leaves, and occasionally small animals), shelter, and mating partners. The availability of these resources dictates the movement patterns of the group within their territory.

Patrolling and defense

Chimpanzees actively defend their territories through regular patrols. These patrols are conducted by adult males who walk silently in single file along the periphery of their territory. 

The primary purpose of these patrols is to find and deter intruders, which can sometimes escalate into aggressive encounters.

Social organization in chimpanzee territory

The control of territory is essential for the social organization of chimpanzee groups. Dominant males often lead the patrols and are central to the defense strategies of the group. 

The maintenance of territory directly affects the reproductive success of the males, as females tend to reside within the territories that offer the best protection and resources.

Conflict and cooperation

Territories are often contested among different chimpanzee communities, leading to skirmishes and sometimes even lethal confrontations. 

However, there is also evidence of cooperation and alliances between groups, which can be strategic for the defense against common threats or enemies.

Chimpanzee territory culture

Recent research has suggested that different chimpanzee communities have unique behaviors and traditions that are passed down, which can be associated with their territories. 

These may include specific grooming habits, tool use, or foraging techniques, further demonstrating the complexity of their social structures.

Understanding chimpanzee territories gives us insight into the evolutionary pressures that may have shaped human ancestors’ behavior regarding land ownership, resource allocation, and group defense. The study of these primates continues to inform scientists about the roots of human sociality and territoriality.

The study is published in the journal PLoS Biology.

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