Group size and visitor numbers predict faecal glucocorticoid concentrations in zoo meerkats.

Katy Scott,Michael Heistermann,Emma I K Vitikainen,Michael A Cant

doi:10.1098/rsos.161017

Abstract

Measures of physiological stress in zoo animals can give important insights into how they are affected by aspects of their captive environment. We analysed the factors influencing variation in glucocorticoid metabolites in faeces (fGCs) from zoo meerkats as a proxy for blood cortisol concentration, high levels of which are associated with a stress response. Levels of fGCs in captive meerkats declined with increasing group size. In the wild, very small groups of meerkats are at a higher risk of predation, while in larger groups, there is increased competition for resources. Indeed, group sizes in captivity resemble those seen in unstable coalitions in the wild, which may represent a stressful condition and predispose meerkats to chronic stress, even in the absence of natural predators. Individuals in large enclosures showed lower levels of stress, but meerkat density had no effect on the stress measures. In contrast with data from wild meerkats, neither sex, age nor dominance status predicted stress levels, which may reflect less food stress owing to more equal access to resources in captivity versus wild. The median number of visitors at the enclosure was positively correlated with fGC concentrations on the following day, with variation in the visitor numbers having the opposite effect. Our results are consistent with the hypothesis that there is an optimum group size which minimizes physiological stress in meerkats, and that zoo meerkats at most risk of physiological stress are those kept in small groups and small enclosures and are exposed to consistently high numbers of visitors.

Highlights

Measuring stress in zoo animals is important to improve welfare and monitor the effect of captivity, but is difficult in practice
Santema [21] found that in stable groups, that tend to be larger (2–32, median = 15), fGC concentrations increase with increasing group size, suggestive of competitive costs of large group size. These results suggest that group size may have complex relationship with measures of physiological stress, depending on the social context, as well as the range of group sizes under investigation
We found that three main factors predicted levels of faecal glucocorticoids in zoo meerkats: the size of their social group, size of the enclosure and the number of visitors that the animals were exposed to, on the day before the sample collection

Summary

Introduction

Measuring stress in zoo animals is important to improve welfare and monitor the effect of captivity, but is difficult in practice. Variation between species and between individual animals in their behavioural responses to a stressor make it difficult to define fixed, reliable criteria for assessing animal welfare based on their rearing conditions [1,2]. Observational measures, such as behavioural repertoire, or breeding success can provide useful information [3]. Large numbers of visitors may be stressful to the animals and linked with changes in their behaviour [4] They may be difficult to interpret and to causally link to a particular set of conditions the animals are experiencing, for example, because the behaviour of the animals could be the driver of variation in visitor numbers, as well as the consequence of it [5,6]. A useful method, is to measure directly how variation in captive conditions and exposure to visitors impacts the physiological response of the animals, by measuring components of the hormonal stress response [7]

Methods

Results

Conclusion