Linking humans, dogs, and patterns of dispersal to stress physiology of California ground squirrels in a semi-urban park

Abstract Given rapid urbanization across the globe, coping with humans is an important aspect of life in the modern world for most animals. Although human presence is often accompanied by human-associated predators such as dogs, the effects of humans and dogs on animal physiology are rarely considered together. Here, we leverage over 4500 measures of fecal glucocorticoid metabolite (FGM) measurements, a biomarker of stress physiology, collected from more than 1200 marked California ground squirrels (Otospermophilus beecheyi) at two sites differing in human activity. Drawing on 12 years of study, we explored the effects of dispersal status, human presence, and dog activity on FGMs in juveniles and adults to uncover the multiple factors contributing to individual and population-level differences in FGMs. Longitudinal data on between-site dispersal revealed site-level effects on FGMs. FGMs decreased after individuals dispersed to the less disturbed site, but generally increased after dispersers moved to the more disturbed site. Detailed cross-sectional data from the more disturbed site further revealed age- and mass-dependent responses to human and dog activity. Whereas dog activity failed to predict juvenile FGMs, juvenile FGMs were highest for individuals trapped in areas with high human activity. In contrast, dogs represented a major stressor for adult animals, but the effects of dogs on adult FGMs were generally shielded by human presence. Together, these findings uncover the complex relationships among anthropogenic factors, stress physiology, and habitat selection over multiple spatial and temporal scales in wild animals living in a human-influenced world.