Captive chimpanzees are one of the most popular species kept in zoos because of their charismatic appeal and similarity to humans. They are the closest living relatives of humans because of the shared genes and behavioural and psychological similarities.

Zoos are ethically bound to care for the animals they house. Many provide environments that care for animals’ welfare needs. However, the impact of zoo environment on the behaviour, psychology and welfare of animals is sometimes overlooked or poorly understood.

Historically, zoos have been criticised and labelled as “animal prisons”. But based on my experience and research, it’s clear that modern zoos play an important multifaceted role as centres of education, recreation, conservation and research.

Chimpanzees have been the focus of much zoo-based research, including research on their welfare. Most people – researchers, zoo workers and the public alike – assume that providing animals with larger, more “naturalistic” spaces to live in improves their welfare and existing evidence suggests that this is usually the case.

Few studies have focused on the long-term effects of these enclosures, however.

A recent paper I co-authored with colleagues fills this gap. We observed a stable group of eight chimpanzees at Johannesburg Zoo in South Africa five years after their outdoor housing was given a revamp to a more naturalistic design. The chimpanzees benefited from the new enclosure. But they appeared to use the space in an unusual way.

We found that the chimpanzees preferred to spend time in the space that was their original enclosure and that they formed groups that were remarkably tightly spaced.

We suggest that the chimpanzees’ perception of space had been altered by their experience of the previous, smaller, barren housing and that this limited their space use in the naturalistic enclosure through what appears to be a self-imposed “invisible cage”.

The role that the “invisible cage” might play in other settings is unclear. However, we believe our findings have implications for animal welfare, husbandry and broader conservation of endangered species.

Our paper shows that zoo-based research can teach us about the needs of animals in our care, and how their environment and experiences shape their biology and behaviour. It can even give us a glimpse into their minds and perceptions.

...continued