Chimpanzees stayed in an ‘invisible cage’ after the zoo was expanded – South African study

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

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

Historically, zoos have been criticized and labeled as “animal prisons.” But based on my experience and research, it is clear that modern zoos play an important multi-faceted role as centers for education, recreation, conservation and research.

Chimpanzees have been the focus of much research in zoos, including research into 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.

However, few studies have focused on the long-term effects of these fences.

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

We found that the chimpanzees preferred to spend time in the space that was their original home and formed groups that were remarkably close together.

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

The role that the ‘invisible cage’ might play in other environments is unclear. However, we believe that our findings have implications for animal welfare, livestock farming and the wider conservation of endangered species.

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


The Johannesburg Zoo will celebrate its 120th anniversary in 2024. Located in Saxonwold in Johannesburg, the zoo covers an area of ​​55 hectares and is the second largest zoo in South Africa. It is home to 320 animal species and is a member of the World Association of Zoos and Aquariums.

In 2004, the outdoor chimpanzee enclosure at the Johannesburg Zoo, built in the 1970s, was extensively modernized. The chimpanzee enclosure was expanded from a pair of concrete and wooden enclosures measuring 10 by 10 meters each, to a large, naturalistic enclosure of approximately 2,500 square meters of grass, shrubs, trees, rocks and streams, on the same site as the chimpanzee enclosure. previous housing. Most of the chimpanzees had lived in the old enclosures all their lives, while two had only lived there for a few years.

Upgrades to naturalistic designs have become the standard for zoos. They are often followed by evaluations to determine how the new space affects the animals’ welfare. Such evaluations generally show that welfare is improved with naturalistic enclosures. This also applied to the Johannesburg Zoo. Chimpanzees showed sustained beneficial behavioral changes, such as reduced abnormal or repetitive behavior, indicating improved well-being in their naturalistic environment.

Our investigation began in 2009, five years after the housing overhaul. This research showed that the chimpanzees used the entire enclosure to some extent, but had a preference for the area where the previous enclosure was located.

Curiously, the chimpanzees also seemed to show a strong tendency to form closely spaced groups that exactly matched the dimensions of the previous housing. These groups formed regardless of when or where the chimpanzees were in the enclosure, the environmental conditions at the time, or which individual chimpanzees were involved.

This unusual pattern had not been previously reported and seemed at odds with what one would expect from a group of animals that had lived in such a large space for five years. This space-use behavior seemed to reflect a perceived, self-imposed, elusive barrier to the distance between the chimpanzees, as if an invisible cage surrounded the groups.

Animal welfare and use of space

Space use is difficult to interpret in terms of animal welfare because it is often context dependent and therefore usually ignored in post-enclosure assessments. When an animal chooses to use a small amount of space, it may be because the space is attractive and meets its welfare needs. However, an animal may choose to stay in a small area because the larger space is perceived as unpleasant or even dangerous.

In the chimpanzees, there was no indication that the spacing pattern indicated distress or compromised well-being. Other aspects of the chimpanzees’ behavior suggested improved welfare in the naturalistic enclosure. Instead, it seemed that the invisible cage reflected a persistent psychological barrier, learned in the previous enclosure and imposed years later in the naturalistic enclosure.

These findings reflect a psychological effect called “learned helplessness,” which occurs in many species, including humans. In situations where individuals are helpless or have no control, they learn that their actions cannot influence the outcome. This perception carries over to later situations where they can influence the outcome, as if they were still helpless.

Further research is needed to understand the well-being implications and broader application of these findings. However, they highlight some important issues surrounding the role of zoos and how zoos influence species conservation.

The importance of zoos

Zoos help raise awareness of conservation issues. They also provide a refuge for endangered species. Many facilities breed and reintroduce these species into the wild. The Johannesburg Zoo in particular has several conservation programs, including a breeding program for the endangered Pickersgill reed frog.

As sanctuaries that sustain endangered populations, zoos actively conserve biodiversity in many ways (by creating gene banks, breeding animals, and maintaining biological and behavioral diversity), while at the same time providing crucial access to rare species for observation and research.

This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Luke Mangaliso Duncan, University of Warwick

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Luke Mangaliso Duncan received funding from the Jane Goodall Institute and the National Research Foundation (NRF) of South Africa.

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