Group size and visitor number predict faecal glucocorticoid concentrations in zoo meerkats

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. Compared to data from wild meerkats, this contrasts with the patterns seen in large stabile groups but matches the pattern seen in dispersing coalitions. 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 tend to be closer to those seen in unstable coalitions in the wild, which may represent a stressful condition to meerkats in captivity and predispose them to chronic stress, even in 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 to data from wild meerkats, neither sex, age, nor dominance status predicted physiological stress levels in captivity, which may reflect less food stress owing to more equal access to resources in captivity versus wild. 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 minimises 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.