Influence Of Human Activity On The Stress-Hormone Levels And Nestling Growth Of Wild Breeding Tree Swallows

Anthropogenic disturbance can influence the physiology of individuals in wild breeding populations and have consequences for population ecology and conservation biology. The response to stressors in daily life is mediated by the hypothalamo-pituitary-adrenal (HPA) axis and can be assessed via concentrations of circulating glucocorticoids. Shortly after exposure, blood concentrations of glucocorticoids increase in response to environmental, social and internal stressors, enabling animals overcome a threatening situation. I tested the hypothesis that level of anthropogenic disturbance influences glucocorticoid concentrations in wild tree swallow nestlings. Across the field site, I qualitatively categorized nests as experiencing high or low levels of human activity. Additionally, I used an experiment in which adult females were repeatedly handled by humans during the time they reared nestlings. Just prior to fledging, I measured morphology and corticosterone (CORT) concentrations from the blood. Results did not match predictions: nestlings that experienced high human activity showed a reduced CORT response in addition to being smaller than nestlings in low activity areas. Since CORT was measured from blood taken 15 minutes after handling, it is possible that nestlings in high activity experienced decreased acute stress response as a result of chronic stress exposure. Repeated handling of mothers had no influence on nestling parameters suggesting effects of anthropogenic disturbance may be a consequence of maternal deposition of CORT in egg yolks. Overall, these data indicate complex interactions between human activity patterns and acute versus chronic stress in nestling Tree swallows.