Chimpanzees and gorillas are naturally territorial creatures. However, they almost always turn that energy inward, squabbling with others of their species to be “king of the hill.”
It was previously unheard of for them to band together and attack across species lines, but researchers in the central African country of Gabon have recently witnessed not one but two distinct instances of just that.
The seemingly unprovoked attacks were first reported in Scientific Reports, where paper authors Lara M. Southern, Tobias Deschner, and Simone Pika discussed possible causes and what this new behavior could mean for conservationists in the future.
“In both events, the chimpanzees significantly outnumbered the gorillas and victims were infant gorillas,” the paper notes. While the groups have interacted peacefully before, often sharing the same fruit-harvesting territory, a shift in behavior occurred in 2019, about 5 years after the team had first started monitoring the populations.
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“The first event occurred after a territorial patrol during which the [male gorillas] made a deep incursion into a neighbouring chimpanzee territory,” the authors wrote. A group of three females, one silverback, and a baby gorilla were confronted by the chimpanzees, who screamed and barked before moving aggressively towards the gorillas. The conflict, which lasted nearly an hour and was caught on video, left the baby gorilla dead and one chimp severely injured, with others experiencing minor scrapes.
The second incident, in December of 2019, followed a similar pattern, with a group of 27 chimpanzees coming across a group of gorillas and initiating aggressive actions. This time, the seven gorillas had been relaxing in the canopy of a large tree, with females caring for infants in its sturdy branches and one silverback nearby.
“At 12:30, the majority of the chimpanzees started to climb up into the surrounding trees, while approximately four adult male chimpanzees remained on the ground… One adult male chimpanzee, Chenge, climbed further up the tree with the gorillas, and stopped within five meters of the silverback and one adult female gorilla with an infant (AF1 and I1). All visible gorillas started to emit alarm barks, and the silverback and the two adult females with their infants moved higher up into the canopy. At 12:36, the silverback rapidly climbed down the tree and fled. The chimpanzees continued barking but did not follow him,” the report stated.
The half-dozen gorillas that remained were now largely defenseless, as the females were carrying infants and the only male that remained was a juvenile, lacking the strength and intimidation of a silverback. The females attempted to climb down the tree and leave, as the silverback had. The chimps blocked their way, and one snatched an infant from its mother before she was able to claw him back.
Twenty minutes after the conflict had started, a second gorilla mother tried to escape with her infant, losing him in the tangle of branches and foliage by the trees. Researchers weren’t able to see exactly what happened next, but shortly after, “an adolescent chimpanzee, Cesar, was seen holding the body of a dead infant gorilla.” The body was eventually taken by a female chimpanzee who ate parts of the corpse including its brain and fingers before discarding it.
The team struggled to explain the never-before-seen behavior but offered a variety of possible causes. It could be that the chimpanzees were on the hunt, looking to scare away the silverback protectors with sheer numbers and then take the infants as a prize, but researchers noted that their behavior after the death of the infant in both cases was not consistent with a typical hunt. In both cases, “excitement levels dropped immediately following the death of the infant gorillas,” and there was little sharing of food in the one case where the infant was eaten.
Researchers also pointed to the fact that both attacks “occurred at times characterized by food scarcity and a period of high dietary overlap,” meaning that chimps and gorillas could have been driven into conflict by competition over scarce resources.
Lastly, they noted that the chimpanzees could have been motivated by “a drive for dominance over neighbours resulting in fitness benefits for the attackers through improved access to resources such as food, females, or safety.”
While this is the first time that researchers have seen conflict between chimpanzees and gorillas on this scale, it’s possible that this has happened in the past and that further research could piece together an explanation. The researchers also noted that watching conflict between primates of different species could illuminate parts of our own human history, and show how our ancestors were able to survive and evolve in the distant past. As competition over resources intensifies, it could also foreshadow potential conflict in the future. Read more about the study and see supplementary information here!Whizzco