Chimpanzees have been observed attacking and killing gorillas in the wild for the first time.
Researchers working in the Loango National Park in the west African country of Gabon witnessed two lethal encounters in which ‘coalitions’ of chimps clashed with gorilla troops, and their findings were published this week in the journal Nature.
In both incidents, the outnumbered adult gorillas came under assault from up to 20 adult and adolescent chimps, and as they attempted to flee they became separated from their infants – who were subsequently killed.
Previously, observed interactions between gorillas and chimps had been relaxed and even playful.
The report authors said more research was necessary to confirm the cause of the deadly attacks.
But they suggest depleted food resources in the Loango National Park, exacerbated by the effects of the climate crisis, could be to blame for growing tensions between the species.
“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,” Tobias Deschner, a primatologist at the Max Planck Institute for Evolutionary Anthropology, and one of the report authors, said.
Other national parks in Gabon have experienced a ‘fruit famine’ in recent years that has upended delicate ecosystems. The chances of an elephant encountering ripe fruit have decreased by 81% since the 1980s, according to a study published earlier this year.
Researchers from Osnabruck University and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have been studying the behaviour of around 45 chimpanzees since 2014.
Each chimp is given a name, and their group composition, hunting behaviour, use of tools, and ability to communicate are carefully documented.
PhD student and lead report author Lara M. Southern observed the first violent attack in 2019.
"At first, we only noticed screams of chimpanzees and thought we were observing a typical encounter between individuals of neighbouring chimpanzee communities,” she wrote.
“But then, we heard chest beats, a display characteristic for gorillas, and realised that the chimpanzees had encountered a group of five gorillas.”
Southern watched a group of 18 chimpanzees encounter five gorillas – a silverback, three females and an infant – in a thicket.
The silverback charged and severely injured a female adolescent named Gia.
Then, a group of 10 chimps surrounded the silverback “and repeatedly jumped down on and hit him whilst screaming and barking”, Nature stated.
The infant became separated from the escaping adults and was beaten and killed by the chimps.
In the second lethal encounter, chimps and gorillas were observed in a series of attacks in trees.
After a silverback fled from another group assault, a group of chimps tried to pull an infant gorilla from its mothers’ arms. It became separated from the mother, and was also killed.
The study authors said they were only just beginning to understand the interactions between the two great ape species, and more research was required.
“Our observations provide the first evidence that the presence of chimpanzees can have a lethal impact on gorillas. We now want to investigate the factors triggering these surprisingly aggressive interactions,” said author Tobias Deschner.