Meeting Abstract
Vertebrates respond to acute stressors by increasing glucocorticoid hormone levels. These increases in glucocorticoids affect many physiological processes, including energy storage, immune function, and behavior. Animals that colonize urban environments are faced with novel anthropogenic stressors, which might induce elevated levels of circulating glucocorticoids and changes in associated traits. Paradoxically, urban animals exhibit bold behavior, which is frequently correlated with low stress response. Thus, while urban environments could be initially stressful, selection for bold personality may lead to a reduced glucocorticoid response in urban animals. In still a third possibility urban animals may attenuate their response to stressors through habituation (learning over the course of the lifetime). Previous comparisons of urban and non-urban birds report differences in corticosterone (cort) response to acute stressors, but the direction of change from ancestral habitats to urban habitats has not been consistent, and no studies have examined multiple urban and non-urban populations of the same species. One urban population of our study species, the dark-eyed junco (Junco hyemalis), is known to have an attenuated stress response compared to a nearby ancestral population. We studied juncos from five cities and six non-urban sites in California from March to July 2014 and asked whether a lower cort response was consistently observed in urban juncos. We measured cort response to acute stress by taking blood samples from free-living juncos within 3 minutes of capture and again 30 minutes later. Results of this first study to compare replicate urban and non-urban populations of one species of bird are pending, and will provide valuable insights into the impact of urbanization on stress physiology.
