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Chimpanzees Were Observed Killing Gorillas For the First Time

The surprising observation may have been caused by food scarcity due to climate change.

A team of researchers observed the first recorded incident of a lethal attack by chimpanzees on gorillas in the wild, which resulted in the death of two infant gorillas, a press statement reveals.

In the past, chimpanzees have generally been observed to coexist peacefully with gorillas, meaning the attacks may have been caused by increased competition for food due to climate change. 

If the harrowing attack is, in fact, down to climate change, it will be the latest in a string of animal behaviors that have been altered directly or indirectly by humans — other examples include migratory birds and also orca whales, which are only known to have caused human fatalities when in captivity.

Humans have greatly altered animal behavior

The incident was recorded at the Loango National Park in Gabon, Central Africa, one of several locations where chimpanzees and gorillas are known to coexist. That park has been home to the Loango Chimpanzee Project, led by Max Planck Institute primatologist Tobias Deschner, since 2005, and Simone Pika, a cognitive biologist at Osnabrück University.

In order to gain a better understanding of the behavior of chimpanzees, the project team has observed and analyzed tool use, hunting behavior, territoriality, communication, and other chimpanzee behaviors for more than a decade.

"Interactions between chimpanzees and gorillas have so far been considered as relatively relaxed," Simone Pika explained. "We have regularly observed both species interacting peacefully in foraging trees. Our colleagues from Congo even witnessed playful interactions between the two great ape species."

However, to their great surprise, the Loango Chimpanzee Project team observed the first-ever documented lethal encounter between chimpanzees and gorillas in 2019.

"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 Tobias Deschner.

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Increased food competition means more aggressive animals

In the Max Planck Institute's press statement, Lara M. Southern, Ph.D. student and first author of a study on the behavior, explained that the researchers first believed they were hearing territorial fighting between chimpanzee communities when they heard the screams of chimpanzees during the first observation in 2019.

However, what came next was a surprise. The team also heard chest-beating, characteristic of gorillas, leading them to the realization that the chimpanzees had encountered a group of five gorillas.

In the observed encounters, which lasted between 52 and 79 minutes, chimpanzees attacked the gorillas in groups while the two silverbacks of the gorilla groups defended themselves and their offspring, alongside the adult females of the groups. During these encounters, two gorilla infants were separated from their mothers and killed.

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"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 explained.

The problem of food scarcity is knowingly exacerbated by the effects of climate change, which has led to a collapse in fruit availability in tropical forests in Gabon. However, the researchers say they must conduct more research to gain a better understanding of what exactly has caused these attacks before they can rule out any other potential causes.

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