Assessing animal welfare in a captive primate: an analysis of stress related behaviour in Mandrillus sphinx

Abstract

The study of stress in captive animals maintained in zoos allows to consider elements that play a main role for the welfare of these species. Among these elements there are the zoo visitors, recently found in the scientific literature as negatively influencing the animals especially when these are primates. At Chester Zoo (UK), a group of six mandrills was investigated after having shown signs of stereotypical behaviour comprised of hair plucking. Through the application of ethology, notably the procedure of all-animal scan sampling, a series of variables was collected. From the data it was tested whether the public's density and the noise produced were responsible for the occurrence of visitor-directed aggression and stereotypies. These data were statistically analysed through mixed effects linear models. This statistical treatment provides a powerful way of testing of data with a degree of interdependency (such as scan samples of a particular individual). Such data are often yielded in studies with low numbers of individuals, as is often the case under captive conditions. The results collected from the zoo visitors found that they used to stay for longer in proximity of the enclosure producing a louder noise when the animals were found in the in-door enclosure and in proximity of the glass window dividing the public. The analysis of the animal behaviour showed that a correlation exists between the visitors’ density and noise and the occurrence of aggressive related displays towards the public by the animals. The visitors' density was also found to be responsible for the higher occurrence of stereotypical bouts of hair plucking. It was hypothesised that the latter was an indirect relationship and resulted from the fact that aggressive behaviours towards visitors did not have the effect anticipated by the mandrills leading to frustration and subsequent hair plucking.