Some captive chimpanzees show signs of compromised mental health, research shows

These include self-mutilation, repetitive rocking, as well as the eating of feces and drinking of urine.

The research, which was conducted by Dr Nicholas Newton-Fisher and Lucy Birkett from the University's School of Anthropology and Conservation and is published by the online journal PLoS ONE, was conducted among 40 socially-housed zoo-living chimpanzees from six collections in the USA and UK. After determining the prevalence, diversity, frequency, and duration of abnormal behavior from 1200 hours of continuous behavioral data, the researchers concluded that, while most behavior of zoo-living chimpanzees is 'normal' in that it is typical of their wild counterparts, abnormal behavior is endemic in this population despite enrichment efforts such as social housing.

Such abnormal behavior has been attributed to the fact that many zoo-living chimpanzees have little opportunity to adjust association patterns, occupy restricted and barren spaces compared to the natural habitat, and have large parts of their lives substantially managed by humans. Controlled diets and provisioned feeding contrast radically with the ever-changing foraging and decision-making processes of daily life in the wild.

To date, published literature on abnormal behavior in wild chimpanzees is sparse and rates of abnormality comparable to those described in the study have never been reported.

Dr Newton-Fisher, a primate behavioral ecologist and expert in wild chimpanzee behavior, said: 'The best zoo environments, which include all zoos in this study, try hard to enrich the lives of the chimpanzees in their care. Their efforts include providing unpredictable feeding schedules and extractive foraging opportunities, and opportunities for normal social interactions by housing chimpanzees in social groups. There are limits to what zoos can provide, however; the apes are still in captivity.

'What we found in this study is that some abnormal behaviors persist despite interventions to 'naturalize' the captive conditions. The pervasive nature of abnormal behavior, and its persistence in the face of environmental enrichment and social group housing, raises the concern that at least some examples of such behavior are indicative of possible mental health problems.

'We suggest that captivity itself may be fundamental as a causal factor in the presence of persistent, low-level, abnormal behavior -- and potentially more extreme levels in some individuals. Therefore, it is critical for us to learn more about how the chimpanzee mind copes with captivity, an issue with both scientific and welfare implications that will impact potential discussions concerning whether chimpanzees and similar species should be kept in captivity at all.'