Scientists have documented what appear to be the first-ever deadly chimpanzee attacks against gorillas, according to a new study published this week in the journal Nature.
Researchers from Osnabrück University and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, were shocked to observe the attacks firsthand in the wild in Loango National Park in Gabon.
The team was there to study and analyse the group behaviour of 45 chimpanzees as part of the Loango Chimpanzee Project in a region where gorillas also live.
Chimps, who share 98.7% of human DNA, are known to be aggressive and have some very basic traits often attributed only to humans. They are patriarchal, ambitious, excitable and violent. They band in aggressive groups to hunt down others often in bloody, brutal and fatal conflict.
But their conflicts are normally internecine, the team said.
“Interactions between chimpanzees and gorillas have always been considered as relatively relaxed,” said study co-author Simone Pika, in a statement. “We have regularly observed both species interacting peacefully while foraging. Our colleagues from Congo even witnessed playful interactions between the two great ape species.”
But on two 2019 research trips the team observed wildly different behaviour.
“At first, we heard screams of chimpanzees and thought we were observing a typical encounter between individuals of neighbouring chimpanzee communities,” said Lara Southern, first author of the study, in a statement.
“But then, we heard chest beating, and realised that the chimpanzees had encountered a group of gorillas.”
In the two encounters, the chimps formed coalitions to attack the gorillas.
The conflict in February involved 18 chimpanzees and five gorillas – one silverback, three adult females and one infant, according to Science Alert.
The chimps came upon the gorillas while returning from an excursion into neighbouring territories.
The second fight, in December, involved 27 chimpanzees, some of them involved in the first incident.
This time there were seven gorillas: one silverback, three adult females, one juvenile and two infants. The chimps found the gorillas at the start of a territory border patrol, Science Alert said.
“The two silverbacks of the two groups and the adult females defended themselves and their offspring,” the researchers said. “While both silverbacks and several adult females escaped, two gorilla infants were separated from their mothers and killed.”
In both battles, the chimps separated an infant gorilla from its mother and killed it, and in the December fight the chimps ate the baby gorilla.
The other gorillas escaped, and some chimps were injured, according to the researchers.
The team is now trying to sort out what may have caused the chimps to be so aggressive.
It could have been that the chimps saw their fellow primates as prey, or were confronting them over territory, or that habitat degradation leading to decreased food sources could have pushed them over the edge, the researchers surmised.
Study co-author Tobias Deschner suggested, “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.”
Despite their intimidating appearance, gorillas are generally docile creatures, much more gentle than their chimp cousins. They also share 98% of human DNA.