Noninvasive fecal monitoring of glucocorticoids in Alaskan brown bears (Ursus arctos horribilis)

Brooks River in Katmai National Park is one o f the most famous bear-viewing areas in the world. The close proximity of brown bears and humans at Brooks River poses a question vital to the management of these bears: do ongoing human activities at Brooks River induce stress in brown bears that rely on this fishing area for much of their nutritional intake? Fecal monitoring of glucocorticoids is a new and noninvasive technique for measuring stress in free-ranging animals and is being applied to an increasing number of species. This technique has never been performed on brown bears. Thus, the aim of this study was threefold; to validate the use of a radioimmunoassay (RIA) for quantifying glucocorticoid metabolite concentrations in feces from brown bears, to apply this technique to a study of impacts of human activities over a four-month period on physiological stress in brown bears along two rivers in Katmai National Park, AK, and to provide recommendations for management based on the results of stress analysis. An established RIA for corticosterone was tested for assay sensitivity, specificity, and sample matrix effects, and proved satisfactory. Fecal samples collected in the wild from brown bears of five month by location treatments were assayed for glucocorticoid metabolite concentrations and analyzed in the presence of covariates measuring current human and bear activities, as well as diet type of each sample. Fecal samples fi-om identified bears were also collected and analyzed for differences among sex-age classes. We observed a significant interaction between the effects of diet types and treatments on fecal glucocorticoid concentrations. There was no evidence of a significant effect of human activities on fecal glucocorticoid concentrations, although confounding in this observational study limits inferences concerning effects of visitor use on bear stress. Sex-age class differences in fecal glucocorticoid concentrations were not observed. This study demonstrates that fecal glucocorticoid concentrations may be assessed in brown bears, but this technique may have limited application in species with complex or seasonal dietary habits.