WADA, H.*; HAHN, T.P.; BREUNER, C.W.; University of Texas, Austin; University of California, Davis; University of Texas, Austin: Stress and development: the role of corticosteroid binding globulin in regulating free corticosterone levels in nestling and fledgling white-crowned sparrows (Zonotrichia leucophrys oriantha)

Elevation of corticosterone (CORT) in response to acute stressors can redirect physiology and behavior to increase survival in adults. However, the stress response may be detrimental in developing individuals, given suppressive effects on growth and immune parameters. While CORT levels have been measured in nestling passerines previously, no study has investigated the role of binding globulins in regulating the accessibility of CORT to the tissues. Corticosteroid binding globulin (CBG) may be elevated early in development, to protect the nestling from surges in free CORT, or CBG may slowly increase as the hypothalamic-pituitary-adrenal axis matures. We investigated the ontogeny and regulation of the stress response (CORT and CBG levels) in nestling and fledgling mountain white-crowned sparrows (Zonotrichia leucophrys oriantha). Blood samples were collected at 0 and/or 30 minutes after capture (in younger nestlings, sampling times were divided between siblings). CBG capacity increases with age in white-crowned sparrow nestlings, and is further increased in fledglings. We are currently quantifying both total and free levels of CORT in these animals to determine the ontogeny of stress response. This will be the first study to examine the role of CBG in regulating the organismal response to stress during development in birds.