For the First Time Ever, Scientists Witness Chimps Killing Gorillas

As the scientists speculate, increased food competition in Loango National Park and possibly elsewhere might be the result of climate change, though more research is needed to be sure.

If this turns out to be the case, however, it’s yet another example of the natural world being turned upside down by human-instigated climate change. Scientists with the Loango Chimpanzee Project have been observing great apes at the park for several years, and they’re learning much about their social relationships, group dynamics, hunting behavior, and communicative abilities.
As the scientists write in their study, these encounters “were always peaceful, and occasionally involved co-feeding in fruiting trees.” And as Osnabrück University cognitive scientist Simone Pika notes in a press release, the team’s colleagues from Congo have even witnessed “playful interactions between the two great ape species.”

So imagine their surprise when, in 2019, the team witnessed not one but two violent encounters, each ending in fatalities.
“Our observations provide the first evidence that the presence of chimpanzees can have a lethal impact on gorillas,” Tobias Deschner, a primatologist at the Max Planck Institute for Evolutionary Anthropology and a co-author of the study, explained in a release from the institute.
“We now want to investigate the factors triggering these surprisingly aggressive interactions,” said Deschner, who leads the Loango Chimpanzee Project alongside Pika. The first encounter, lasting for 52 minutes, happened on February 6, 2019, and it “occurred after a territorial patrol during which the males made a deep incursion into a neighboring chimpanzee territory,” according to the study.
“At the first encounter, when we heard the initial chimpanzee screams, we actually thought our chimps had bumped into another group of chimpanzees,” Lara Southern, a Ph.D. student at Max Planck Institute for Evolutionary Anthropology and first author of the study, explained in an email.
“It was only when we heard the first chest beat, a sound which only gorillas make, that we knew something different was about to happen.”

A group of 27 chimps attacked five gorillas—two male silverbacks, two adult females, and one infant.
“In both cases, once the first chimpanzee who saw the gorillas let out an alarm bark or scream, the majority of other group members reacted immediately and joined in, all barking together,” noted Southern.
“The chimpanzees then worked together to single out certain gorillas, and in both events, they were able to separate the baby gorillas from their mother.”

Jessica Mayhew, a biological anthropologist at Central Washington University, said primates adopt different strategies to navigate both intragroup and intergroup conflict and that chimps and gorillas exhibit very different approaches in this regard.
“If you study chimpanzees, you come to expect that any squabble can quickly turn lethal, which is a testament to their excitability but also their incredible speed and power,” Mayhew, who wasn’t involved in the study, explained in an email.
Life for a young gorilla is quite dangerous—infant mortality is high—and this study again highlights their vulnerability within a group even with a formidable silverback as a dad.”

Large silverbacks can weigh as much as 590 pounds (270 kg), but chimps have ferocious strength.
“Considering that female western gorilla can be almost twice the weight of a typical 100-pound male chimpanzee, while male gorillas can be three to four times as heavy as a male chimpanzee, the fact that chimpanzees can steal an infant gorilla from its mother is remarkable,” Richard Wrangham, an evolutionary biologist at Harvard University, said in an email.
“By looking at the current pressures faced by these two species, both in their environment and in the way they interact socially, we may learn a little more about how we as humans, so to speak, ‘rose to the top,’” she wrote.
“It is crucial, now more than ever, that we work to protect these endangered species who provide a window into our past and deserve a place in this future.”

As to why the chimps attacked gorillas in these two instances, that’s not entirely clear.
For Wrangham, however, the chimpanzee attack on the gorillas was not very surprising, given their interest in killing. As for other possibilities, Southern said they can “only really guess as to why this happened,” but they have some theories.
One possibility is that the chimps wanted to hunt gorilla infants as a prey, but seeing that only one chimp expressed any interest in this, and given the risks involved, it doesn’t really add up.
“It also could be possible that at certain times of the year when the favorite fruits of chimpanzees and gorillas are at their ripest, there are super high levels of competition between the two apes,” Southern explained.
“If this competition gets intense enough, it may even lead to the kind of violence we observed.”

To which she added: “We think that at Loango, gorillas are perceived as strong competitors by chimpanzees, for both space and food use, much in the way that our group [at Loango] see other enemy chimpanzees.”

Which is a very good point.
As the Max Planck Institute release points out, fruits in the tropical forests of Gabon are not as abundant as they used to be, and human-caused climate change might have something to do with that.
More research will be needed, especially sightings of repeat conflicts between chimps and gorillas (both at Loango and elsewhere) and investigations showing the effects of deforestation, climate change, and other factors that could be changing the way these apes use their forest space and interact with one another.
As Mayhew explained, these types of pressures can push ape populations closer together, resulting in more frequent encounters and increased competition over food.“At the moment, I think it’s safe to say that this is an outlier event, but as the authors point out, there’s quite a bit to unpack at this site in terms of the types of pressures being placed on these two ape species,” said Mayhew.

1 week, 1 day ago by Masoumeh Shafiei
Animals

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