Methodological considerations for using fecal glucocorticoid metabolite concentrations as an indicator of physiological stress in the brown bear (Ursus arctos)

Abstract

Reliable methods to measure stress-related glucocorticoid responses in free-ranging animals are important for wildlife management and conservation. Such methods are also paramount for our ability to improve our knowledge of the ecological consequences of physiological processes. The brownbear (Ursus arctos) is a large carnivore of ecological and cultural importance and is important for management. Here, we provide a physiological validation for an enzyme immunoassay (EIA) to quantify glucocorticoid metabolites in brown bear feces. We also provide an evaluationof the effects of sample exposure to ambient temperature on measured fecal glucocorticoid metabolite (fGCM) concentrations. We evaluated three EIA systems: a cortisol assay, an 11- oxoetiocholanolone assay, and an 11b-hydroxyetiocholanolone assay. Of these, the cortisol assay provided the best discrimination between peak fGCM concentrations detected 1–4 d after injections of synthetic adrenocorticotrophic hormone and preinjection baseline concentrations in four individual brown bears. The time of exposure to ambient temperature had substantial but variable effects on measured fGCM concentrations, including variation both between samples from the same individual and among samples from different bears. We propose that the validated EIA system for measuring fGCM concentrations in the brown bear could be a useful noninvasive method to monitor stress in this species. However, we highlight that this method requires that fecal samples be frozen immediately after defecation, which could be a limitation in many field situations.