The effects of age, season, and gender on serum cortisol levels in the tammar wallaby, Macropus eugenii

Serum cortisol levels were measured in a total of 73 tammar wallabies maintained in a captive population at Macquarie University, NSW, Australia. Previous studies of corticosteroids in marsupials have generally involved low sample numbers, a diverse array of analytical techniques, and a variety of sampling conditions. We have conducted a substantive, longitudinal study of serum cortisol levels using a radioimmunoassay protocol, and data have been analysed with respect to age, sex, and seasonality. There were no apparent effects of age or sex on serum cortisol levels, although an inverse but non-significant relationship was observed between males and females. However a significant difference in serum cortisol levels was observed between seasons, with mean serum cortisol significantly higher in summer than in autumn. These data will serve as a reference for ‘normal’ ranges of serum cortisol levels, particularly in the female tammar wallaby. As deviations from these values can indicate compromised animal health and well-being, this information will assist wildlife managers in assessing and monitoring the health status of individuals in captive and free-ranging populations.