Gloria Dickie via the Guardian:

‘[O]n a June day in 2015… Mitani and his fellow researchers were observing a cluster of the group when the chimps began to display nervous behaviour and scattered at the sounds of approaching group members. “All of a sudden, the individuals I was following just ran down the hill for no apparent reason,” Mitani says. “Chaos erupted. They started to run around and chase each other.”

That moment, in retrospect, was the first sign of what would become a years-long bloody conflict – chronicled in the 2023 Netflix series Chimp Empire – between a once close-knit group of chimps. In a study published this April in the journal Science, Mitani and his colleagues describe what may be the first “civil war” among wild chimps.

By 2018, two distinct chimp groups had formed in Ngogo. Nine males and 19 infants have been killed during the conflict. Scientists later found that the unexpected result of this lethal aggression was that female fertility doubled and offspring survival increased substantially at Ngogo….’