Monitoring physiological stress in semi-free ranging populations of an endangered Australian marsupial, the Greater Bilby (Macrotis lagotis)

Rapid and reliable physiological evaluation of stress is necessary for understanding the potential impacts of environmental changes on managed populations of threatened mammals. In situ populations of Australia's iconic marsupial, the greater bilby (Macrotis lagotis), are nearing extinction due to the impacts of competition and predation by feral animals and unpredictable climatic events (summer heat waves). In this study, we focussed our aim to identify a non-invasive method to measure adrenal activity in the species and also to identify potential factors that should be considered when comparing physiological stress in semi-free ranging populations of the species. We validated an enzyme immunoassay (EIA) for detecting fecal cortisol metabolites (FCM) from fresh fecal pellets taken from bilbies within four captive sites and two semi-free ranging populations around Queensland and New South Wales, Australia. Our FCM EIA successfully detected the 'raise and fall' pattern of FCM levels within 3 days of exogenous adrenocorticotropic hormone (ACTH) challenge. Mean FCM levels differed significantly between the captive sites and between sexes. All male bilbies grouped outdoor in captivity expressed the highest mean FCM level in comparison to all captive males that were housed individually or as groups indoors. Also, semi-free ranging bilbies expressed higher mean FCM levels than the captive bilbies. Overall, our study successfully validated a non-invasive tool for monitoring physiological stress in the greater bilby. In the future, it will be worthwhile to consider factors such as housing conditions, sex and location when comparing the adrenal sensitivity to environmental changes, to help evaluate the success of management interventions (such as predator free enclosures) and support the survival of the species.