Bonobos keep track of groupmates even when they can’t see them, study finds

Kanzi, a bonobo celebrated for his intelligence, died in March this year. A recently published study adds to his long list of cognitive abilities: he was able to track the location of people familiar to him, even when they were out of sight. He could also recognize the individual voices of his caretakers, a skill that has never before been tested in bonobos (Pan paniscus).

Kanzi was 44 years old when he died. He lived much of his life at the Ape Cognition and Conservation Initiative in Des Moines, Iowa. For the latest study, conducted in 2023, researchers set up a barrier with three panels and had two caretakers familiar to Kanzi hide behind them. An experimenter held up a photo of each hiding caretaker and asked Kanzi to point to the panel where they were hiding. Kanzi got the answer right more often than just by chance.

In a related experiment, the researchers wanted to see if Kanzi could recognize the same people by voice. So, while hidden behind the barrier, the caretaker said “Hi Kanzi” loud enough for Kanzi to hear them. Then the experimenter showed Kanzi a photograph of the caretaker and asked Kanzi to point to where they were hiding. In this experiment, too, Kanzi got the answer right more often than by chance, suggesting he had “the capacity to use voice as a marker for identity,” Luz Carvajal, lead author of the study and Ph.D. candidate at Johns Hopkins University, said in a press release.

The study results suggest that bonobos place great value in tracking social partners, Carvajal said. “There is definitely a high value in knowing where others are, especially if you think about the dangers of finding yourself alone and stranded from your group,” Carvajal told Mongabay in an email.

Researchers suspect that this ability is not unique to Kanzi, despite his unusual life of language training and interaction with humans. In the wild, bonobos are highly social and live in large groups. In their dense forest homes in Central Africa, it can be easy to lose sight of groupmates, “so to maintain group cohesion, to be safer from predators and to get all the benefits of sociality it makes sense for them to remember their groupmates and where they go,” Carvajal said.

This ability to track important members of their group even when they aren’t directly visible is likely a pillar of how bonobos navigate their physical and social world, Carvajal said.

Similar abilities to track groupmates have been observed in vervet and howler monkeys, but only one other great ape is known to share the bonobos’ tracking ability: humans.

“That humans and our closest ape relatives share this representational machinery suggests that it was present at least 6-9  million years ago in our common evolutionary ancestor,” the study authors note.

Banner image: of Kanzi by William H. Calvin via Wikimedia Commons (CC BY-SA 4.0).