BackgroundMany captive chimpanzees (Pan troglodytes) show a variety of serious behavioural abnormalities, some of which have been considered as possible signs of compromised mental health. The provision of environmental enrichments aimed at reducing the performance of abnormal behaviours is increasing the norm, with the housing of individuals in (semi-)natural social groups thought to be the most successful of these. Only a few quantitative studies of abnormal behaviour have been conducted, however, particularly for the captive population held in zoological collections. Consequently, a clear picture of the level of abnormal behaviour in zoo-living chimpanzees is lacking.MethodsWe present preliminary findings from a detailed observational study of the behaviour of 40 socially-housed zoo-living chimpanzees from six collections in the United States of America and the United Kingdom. We determined the prevalence, diversity, frequency, and duration of abnormal behaviour from 1200 hours of continuous behavioural data collected by focal animal sampling.Results, Conclusion and SignificanceOur overall finding was that abnormal behaviour was present in all sampled individuals across six independent groups of zoo-living chimpanzees, despite the differences between these groups in size, composition, housing, etc. We found substantial variation between individuals in the frequency and duration of abnormal behaviour, but all individuals engaged in at least some abnormal behaviour and variation across individuals could not be explained by sex, age, rearing history or background (defined as prior housing conditions). Our data support a conclusion that, while most behaviour of zoo-living chimpanzees is ‘normal’ in that it is typical of their wild counterparts, abnormal behaviour is endemic in this population despite enrichment efforts. We suggest there is an urgent need to understand how the chimpanzee mind copes with captivity, an issue with both scientific and welfare implications.
1. Plaice, sole and perch were fed on live food for 20-40 days, and their growth rates were compared with their rates of absorption, both measured as mg. N/g. live weight/day.
2. The gross efficiency of nitrogen conversion--that is, the growth per unit of nitrogen absorbed in excess of maintenance--was between 27.5% and 49.0%.
3. The maintenance rate of absorption was between 0.173 and 0.499 mg. N/g./day.
4. The basal rate of excretion amounted to 0.056-0.208 mg. N/g./day.
5. At maintenance, total excretion is equal to the amount of nitrogen absorbed from the food. The metabolic cost of growth was 1.04-2.64 mg. N excreted per mg. N retained.
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