Bonobos are a social species, living in groups like at this sanctuary in the Democratic of Congo.

In the wild, they often live in dense forest areas.

So can they keep track of their group members, even when they are hidden by undergrowth?

A new study suggests they can - remarkably well.

Researchers carried out experiments with Kanzi, a bonobo born in captivity in the US.

He had learnt to understand spoken English and could communicate with humans using hand gestures and lexigram symbols.

"One of the challenges we have when trying to study the minds of other animals is that they can't talk. So whereas you might just ask people what they think or what's going on in their minds, we can't do that with animals," explains Christopher Krupenye, Assistant Professor of Psychological and Brain Sciences, John Hopkins University and senior author of the report.

"So in this case, the way we tried to get around that was presenting a bonobo with a setup where he could view multiple barriers, really huge barriers that people could fit behind. And one at a time, he would watch several different people hide behind different barriers. And the idea here was that he needed to keep track of which person was behind which barrier. And then we would show him a picture of one of those individuals, the face of one the individuals, and his job was to point at whichever barrier he thought that that person was hidden behind."

This is the first time a study has been conducted in a controlled environment to test whether any animal can mentally track its groupmates.

During these hide-and-seek experiments, Kanzi showed he could track multiple people as they hid behind the barriers.

The bonobo didn't keep a perfect record during the trial - but he got it right often enough to show statistically that he wasn't making lucky guesses.

"He did very well at this task. So Kanzi performed above chance. He was successful the majority of times at finding the correct individual, not just where someone was, but where the individual who was prompted was. And we looked at the data and were able to rule out all kinds of other simpler explanations, leaving the interpretation that he really held in mind not just one individual, but multiple individuals, and was able to indicate their location even after a short delay," says Krupenye.

In a further experiment, people hid behind barriers and then called out to Kanzi.

He was then able to identify where each individual human was based only on their voice.

This ability had never been tested on bonobos before.

The results of the study also shed light on human evolution.

"It tells us something about ourselves. It tells us that these rich features of our social minds, at least their foundations, are shared with other species and are likely evolutionarily ancient components of our social intelligence. But it also tells us about them, about the rich social lives that they're leading in their natural environments and in captivity. And these are, unfortunately, all endangered species. So if we want to even selfishly understand ourselves, I think this kind of work compels us to invest in their conservation," says Krupenye.

For bonobos, tracking their group when they are out of sight, either by remembering their position or by recognising their voices, is a huge advantage when living in dense forests.

The study was published today in the scientific journal Proceedings of the Royal Society B.

Kanzi, the bonobo studied as part of this research, died on 18 March 2025.