Fecal glucocorticoid assays and the physiological stress response in elk

Fecal glucocorticoid assays provide a potentially useful, noninvasive means to study physiological responses of wildlife to various stressors. Consequ ently we quantified fecal glucocorticoid concentrations among free-ranging elk (Cervus elaphus) by subherd, sex, and season and determined their relat ionship to various human activities and environmental conditions. Using a v alidated technique, we assayed 558 fecal samples collected from 30 radiocol lared elk in the Black Hills, South Dakota, from June 1995 to September 199 7. Fecal glucocorticoid measures were least in winter ((x) over bar = 17.41 ng/g, SE = 2.97 for bull subherds and 18.9 ng g, SE = 2.85 for cow subherd s) and increased to peak concentrations in summer ((x) over bar = 33.6 ng/g , SE = 3.42 for bull subherds and 34.21 ng/g, SE = 3.71 for cow subherds). Vehicle use along primary roads, primary road density, and mean temperature each independently explained a significant portion of the variation in fec al glucocorticoid concentrations (r(2) = 0.61, F-2,F- (557) = 286.13, P < 0 .001). Annual glucocorticoid secretion also may be related to normal season al metabolic rhythms. Though more research is needed on fecal glucocorticoi d concentrations of undisturbed elk, we hypothesize that human activities, high temperatures, or normal seasonal metabolic rhythms may have elevated s ummer glucocorticoid concentrations. Our findings suggested that fecal gluc ocorticoid assays, if coupled with population performance measures, could a ssess physiological effects of natural and human-induced disturbances on fr ee-ranging elk. Also, our study illustrated the need for caution when inter preting fecal glucocorticoid measurements, because several confounding fact ors may influence interpretation.