Meeting Abstract
Some bird species are colonizing urban habitats, indicating their ability to adapt to altered light, noise, food resources, and disturbance. Urban birds’ corticosterone (cort) responses to acute stressors differ in magnitude from non-urban conspecifics in many species. In the dark-eyed junco (Junco hyemalis), individuals residing in urban areas have a lower cort response to capture and handling stress than non-urban birds during the early breeding season. This urban phenotype could be the result of past selection, developmental plasticity, or physiological flexibility. To determine whether physiological flexibility could account for observed patterns, we tested whether exposure to frequent disturbance could induce an attenuated cort response over a short time frame in captive adult dark-eyed juncos derived from a non-urban population. Experimental subjects experienced 30-minute psychological stressors four times per day for 21 days; controls were disturbed only during animal husbandry. This treatment occurred during the springtime period of gonadal recrudescence and migration, which is critical in preparing for a successful breeding season. We found that frequently disturbed birds had a lower acute cort response, and some of the difference between groups was due to the seasonal increase in cort response in control birds. Baseline cort did not differ between groups. On average all birds gained weight over the course of the experiment, but frequently disturbed birds gained less weight. We conclude that adult juncos are capable of expressing an attenuated acute cort response in an environment with high frequency of disturbance, which may help to account for their ability to colonize urban habitats. We discuss these results in the context of large-scale field observations of urban and non-urban juncos.
