Lethal chimpanzee attacks on gorillas observed for first time

Chimpanzees and gorillas are generally relaxed around each other in the Loango National Park in Gabon – but recently violent encounters have been documented, according to a study published in the journal Nature.

Researchers from Osnabruck University and the Max Planck Institute for Evolutionary Anthropology in Leipzig are unsure whether the attack came as a result of competition for food or for other reasons, and are continuing to investigate.

The researchers’ work focuses on the behaviour of around 45 chimpanzees in the park, whose group composition, social relations, interactions with neighbouring groups, hunting behaviour, tool use and communicative skills are of interest to the anthropologists.

“Interactions between chimpanzees and gorillas have so far been considered as relatively relaxed,” said Professor Simone Pika at Osnabruck.

“We have regularly observed both species interacting peacefully in foraging trees. Our colleagues from Congo even witnessed playful interactions between the two great ape species.”

So what exactly happened here? As recalled by the study’s first author, Lara Southern, the first attack took place in 2019: “At first, we only noticed screams of chimpanzees and thought we were observing a typical encounter between individuals of neighbouring chimpanzee communities.

“But then, we heard chest beats, a display characteristic for gorillas, and realised that the chimpanzees had encountered a group of five gorillas.”

In the first of the two encounters, which lasted 52 and 79 minutes, the party of 27 chimpanzees formed a coalition to attacked a group of five gorillas.

In the second encounter, also involving a part of 27 chimpanzees, the coalition attacked a group of seven gorillas.

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“The first event occurred after a territorial patrol during which the males made a deep incursion into a neighbouring chimpanzee territory. The second event happened at the start of a suspected territorial boundary patrol,” the study said.

“The first encounter resulted in one dead gorilla infant and three injured chimpanzees; the second resulted in one dead gorilla infant. While there was no indication of consumption of the dead gorilla infant in the first encounter, the infant in the second encounter was almost entirely consumed by one adult chimpanzee female,” according to the study.

It noted: “The main aggressors in both events were adult male chimpanzees.”

According to the researchers the inter-species violence could have been caused by hunting and food competition.

“It could be that sharing of food resources by chimpanzees, gorillas and forest elephants in the Loango National Park results in increased competition and sometimes even in lethal interactions between the two great ape species,” said Dr Tobias Deschner.

“We are only at the beginning to understand the effects of competition on interactions between the two great ape species in Loango,” added Professor Pika.

“Our study shows that there is still a lot to explore and discover about our closest living relatives, and that Loango National Park with its unique mosaic habitat is a unique place to do so.”