Deadly clashes between groups of chimpanzees and gorillas observed

Two adult males of the Loango Chimpanzee Project (Photo courtesy LCP, Lara M. Southern. All rights reserved)
Two adult males of the Loango Chimpanzee Project (Photo courtesy LCP, Lara M. Southern. All rights reserved)

An article published in the journal “Scientific Reports” reports the observation of two clashes that took place in the Loango National Park, Gabon, between groups of chimpanzees and gorillas that led to the death of two gorilla infants and the injury of three chimpanzees. Lara M. Southern, Tobias Deschner, and Simone Pika reported the chronicle of these two unprecedented clashes since until the first clash the relationships between the two species seemed even friendly. Among the possible explanations is a decline in the availability of fruit that affected various parts of Gabon due to climate change and may have triggered the competition for food up to these outbreaks of violence.

Dr. Tobias Deschner, a primatologist at the Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany, has been leading the Loango Chimpanzee Project since 2005. Together with Professor Simone Pika, a cognitive biologist at the University of Osnabrück, he observes the behaviors of a group of about 45 chimpanzees to study their interactions, their habits, their use of tools, and communication skills. Ph.D. student Lara M. Southern worked with them during the time of the clashes reported in the article.

The interactions of the chimpanzees also include those with the gorillas of the area, with whom the relationships were considered rather relaxed. Other researchers in Congo even saw playful interactions between the two species while deadly clashes have never been documented. That changed in 2019.

The first confrontation took place on February 6, 2019. A group of 18 chimpanzees met 5 gorillas and immediately began exchanges of aggressive screams, which lasted several minutes. Subsequently, the menacing screams left the field to physical violence. The silverback, an adult male gorilla, injured a female chimpanzee while an infant gorilla was killed by chimpanzees. The battle ended with the retreat of the surviving gorillas.

The second clash took place on December 11, 2019. A group of 27 chimpanzees came across a female gorilla, immediately joined by a silverback, two adult females with infants, and a juvenile gorilla. Human observers were spotted by the silverback and were forced to move away to avoid getting attacked too. In this case, the physical confrontation occurred in particular between some of the chimpanzees and a female gorilla, forced to retire without her infant. Another unprecedented behavior on the part of the chimpanzees was to eat the killed gorilla infant.

The behaviors observed in chimpanzees are different from those they have during hunting. Clashes with gorillas characterized by behaviors such as forming coalitions against another group and infanticide suggest competition for food at a time when there was a certain scarcity of the foods that are part of the diet of both species.

The researchers offered some hypotheses about the cause of the chimpanzee’s aggressive behaviors. The environmental deterioration that resulted in a decline in fruit availability in several areas of Gabon may have spurred competition for food. It’s known that chimpanzees can be violent but the attacks observed were conducted by large groups that could face the gorillas in clashes that are far out of the ordinary.

Loango National Park offers the opportunity to observe great apes in a natural habitat. Studies of their behaviors take a very long time, so the researchers are just beginning to understand certain interactions, including the ones related to competition for food that can lead to physical violence.

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