Meeting Abstract
As the world becomes increasingly modified by humans, many wild animals are facing novel suites of environmental stimuli. Chronic stressors, such as sublethal effects imposed by predators, including humans, may negatively influence the stress physiology of wild animals. Because California ground squirrels (Otospermophilus beecheyi) face both naturally occurring and anthropogenic threats, they provide a useful model for exploring relationships between predator exposure, human activity, and stress physiology. Here, we use a fully-validated and minimally-invasive enzyme-linked immunosorbent assay (ELISA) to measure fecal corticosterone metabolites (FCMs) of free-living O. beecheyi in northern California. As part of a long-term study of marked individuals, we monitored FCMs from individuals of both sexes across ontogeny and over multiple seasons, study sites, and years. We did this in an effort to explain the endogenous and environmental factors shaping baseline stress in these animals. Although adults tended to have the highest FCM levels, the effects of mass on FCM levels varied with the sex of the animal and its day of capture within the year. Beyond these effects, our study reveals significant differences between study sites, a finding that is consistent with the hypothesis that increased predator pressure from humans and off-leash dogs represents a stressor for these wild animals. Moreover, our analysis revealed that FCM levels vary with time of day and across years of the study. Taken together, our results suggest that the stress responses in free-living mammals are shaped by multiple endogenous and environmental factors, including encounters with humans.
