Chimpanzees Use Military Tactics on Rivals

For decades, biologists and anthropologists believed that complex military strategy was unique to humans. While animals fight for territory, the use of tactical maneuvering, such as reconnaissance and risk assessment, was thought to require human-level cognition. However, a groundbreaking study published in the journal PLOS Biology has turned this assumption upside down. Researchers have observed wild chimpanzees in West Africa using high ground to spy on rival groups, a tactic strikingly similar to human military reconnaissance.

This behavior suggests that the cognitive building blocks for warfare may have existed in the common ancestor of humans and chimpanzees millions of years ago. By analyzing movement patterns and decision-making in the dense forests of Côte d’Ivoire, scientists have provided the first evidence of non-human animals using terrain for tactical advantage during territorial conflicts.

The Taï National Park Study

The research took place in the Taï National Park in Côte d’Ivoire (Ivory Coast), a dense tropical rainforest that is home to several communities of western chimpanzees. Led by Sylvain Lemoine, a biological anthropologist at the University of Cambridge and the Max Planck Institute for Evolutionary Anthropology, the team spent three years tracking two neighboring chimpanzee communities.

Between 2013 and 2016, researchers followed the animals for more than 21,000 hours. They used GPS trackers and direct observation to map the chimps’ movements, specifically focusing on how they interacted with the border zones between their territories. The terrain in Taï National Park features rocky outcrops known as “inselbergs,” which rise above the forest canopy. These formations became the focal point of the study.

The data revealed a clear pattern. The chimpanzees did not climb these hills randomly. They specifically ascended these inselbergs when traveling toward the boundaries of their territory. This behavior indicates a deliberate effort to gather information before proceeding into potentially hostile zones.

High Ground Reconnaissance

In human warfare, taking the high ground is a fundamental tactic. It provides a vantage point to spot enemy movements and assess strength. The study found that chimpanzees use inselbergs for the exact same purpose, although their primary tool is hearing rather than sight.

Because the Taï forest is incredibly dense, visibility is limited. Chimpanzees cannot see rival groups through the thick vegetation. Instead, they climb the rocky outcrops to escape the noise of the canopy and listen for the “pant-hoots” of enemies.

The researchers noted specific behavioral changes during these reconnaissance missions:

• Radio Silence: While on the high ground, the chimpanzees remained remarkably quiet. They suppressed their own vocalizations to avoid detection while listening for rivals.
• Extended Pauses: The patrol groups spent measurable time resting on these summits, seemingly processing the auditory information they gathered.
• Directional Focus: The animals turned their attention toward the known territory of their rivals, indicating they were specifically scanning for threats.

This acoustic surveillance allowed the chimpanzees to estimate the distance and number of rival individuals nearby.

Risk Assessment and Strategic Advancement

The most critical part of the study was not just that the chimps gathered information, but how they acted on it. The research team found a direct correlation between what the chimps heard and how they moved afterward. This decision-making process mimics a military concept known as risk assessment.

When the chimpanzees on the hill heard rivals that were far away (approximately 3 kilometers or more), they were likely to advance into the enemy territory. This suggests they felt safe enough to encroach on rival land to forage or patrol.

Conversely, if they heard rivals that were close (within 1 kilometer), or if the rival group sounded numerous, the reconnaissance team would retreat or avoid the area entirely. This behavior aligns with “Lanchester’s Square Law,” a military theory that predicts combat outcomes based on the relative size of opposing forces. The chimpanzees instinctively understood that engaging a large or nearby enemy force carried a high risk of injury or death.

Implications for Human Evolution

The findings from Sylvain Lemoine and his team offer a new window into the evolutionary history of warfare. The ability to use the environment for tactical advantage requires complex cognitive skills. It involves anticipating the location of enemies, understanding the value of information, and making collective decisions based on incomplete data.

Since chimpanzees and humans split from a common ancestor roughly 6 to 7 million years ago, this study implies that the cognitive roots of warfare are ancient. It suggests that strategic violence is not purely a product of human culture or civilization but may be a deep-seated evolutionary adaptation used to secure resources and territory.

The chimpanzees in the Taï National Park demonstrate that “primitive” warfare is far more sophisticated than random aggression. It involves planning, patience, and the strategic use of geography.

Defining Territory and Border Patrols

The stakes of these tactical maneuvers are high. Chimpanzee communities are fiercely territorial. Losing territory often means a loss of food resources and access to mates. In extreme cases, a larger group may systematically wipe out a smaller community to annex their land.

The border patrols observed in the study function similarly to a border guard. Adult males typically form these patrol units. They move in single file, silent and alert. The use of the inselbergs allows them to expand their territory safely. By confirming that enemies are distant, they can push the “front line” of their territory forward, securing more fruit trees and resources for their females and offspring.

When they detect a threat through their hilltop surveillance, they do not engage in a suicidal charge. They withdraw to protect the core of their community. This balance of aggression and caution is the hallmark of successful military strategy.

Frequently Asked Questions

What specific species of chimpanzee was observed in the study? The study focused on western chimpanzees (Pan troglodytes verus), a subspecies found in West Africa. These populations are known for their distinct behaviors, including nut-cracking and complex social structures.

Did the chimpanzees fight when they encountered rivals? While the study focused on reconnaissance, lethal aggression does occur. If a patrol group encounters a lone individual from a rival community, they may attack and kill them. However, the high-ground tactic is used primarily to avoid dangerous clashes with large enemy groups.

How do the researchers know the chimps were listening? The researchers correlated the sounds recorded in the forest with the behavior of the chimps. They analyzed the acoustic environment and found that the chimps were most likely to advance when rival sounds were distant or absent, and most likely to retreat when rival sounds were loud and close.

Is this behavior found in other animals? While many predators use stealth, the specific use of topography (terrain) for gathering information to make strategic decisions about territory is rarely observed outside of humans and primates. Meerkats use sentries, but that is generally for predator avoidance rather than territorial expansion against rivals.