Experts observing dozens of chimpanzees in Gabon’s Loango National Park expected them to be relaxed around gorillas.
But while both species were generally playful, researchers were surprised to witness occasional vicious attacks.
“At first we only noticed chimpanzee calls and thought we were seeing a typical encounter between individuals from neighboring chimpanzee communities,” said Lara M. Southern, lead author of the study, in A press release.
“But then we heard chest pounding, a characteristic manifestation of gorillas, and we realized that the chimpanzees had encountered a group of five gorillas,” she added, referring to the first attack that the team saw, in 2019.
The two encounters they recorded, which lasted 52 and 79 minutes, saw the chimpanzees forming coalitions and launching attacks on the gorillas.
The silverback gorillas and adult females defended themselves and their offspring. The silverbacks and several adult females escaped, but two baby gorillas were separated from their mothers and killed, the authors wrote.
“Our observations provide the first evidence that the presence of chimpanzees can have a lethal impact on gorillas. We now want to study the factors triggering these surprisingly aggressive interactions,” said Tobias Deschner, primatologist at the Max Planck Institute for Evolutionary Anthropology.
The attacks were particularly surprising considering how the two groups of animals had behaved before. “Interactions between chimpanzees and gorillas have so far been considered relatively relaxed,” said Simone Pika, cognitive biologist at the University of Osnabrück.
“We have regularly observed the two species interacting peacefully in the trees foraging for food. Our colleagues in Congo have even witnessed playful interactions between the two species of great ape,” said Pika.
About 45 chimpanzees were seen for the study, which aimed to analyze their relationships, tool use, communication, and hunting skills, among other characteristics.
The authors suggested that pooling food with other species may have caused the flare-ups. “It could be that the sharing of food resources by chimpanzees, gorillas and forest elephants in Loango National Park could lead to increased competition and sometimes even deadly interactions between the two great ape species,” Deschner said.
Loango National Park is a large protected area on the Gabonese coast in western sub-Saharan Africa. It is home to elephants, buffaloes and a number of other species.
The region is home to the critically endangered western lowland gorilla.
Chimpanzees are an endangered species, according to the International Union for the Conservation of Nature.