Meeting Abstract
Corticosterone is the primary glucocorticoid regulating physiological responses to stressful stimuli in birds and is regulated through the hypothalamic-pituitary-adrenal (HPA) axis. Environmental conditions are known to influence stress physiology with higher corticosterone secretion often selected for in birds coping with harsher unpredictable conditions. Two closely related subspecies of white-crowned sparrow (Zonotrichia leucophrys) are exposed to different fluctuations in environmental conditions. Migratory Gambel’s white-crowned sparrows (Z. l. gambelii) breed in the Arctic and are faced with an unpredictable inclement environment. Resident Nuttall’s white-crowned sparrows (Z. l. nuttalli) in coastal California are found year-round in temperate conditions with little exposure to environmental fluctuations. Here we tested the hypothesis that the corticosterone response to capture and restraint stress would be higher in migrants compared to residents. Blood samples were collected during breeding, pre-basic molt, and during wintering and analyzed by radioimmunoassay. Corticosterone in males was higher in migrants compared to residents during breeding and pre-basic molt while this relationship was reversed for the wintering stage. In females, corticosterone was higher in residents during winter while no other differences were found. Differences between the subspecies suggest that ecological and environmental conditions play a major role in determining HPA axis activity. Studies are currently underway to understand the mechanisms underlying these differences.
