Meeting Abstract

47.4  Jan. 6  SEASONAL CHANGES IN BASAL AND STRESS-INDUCED PLASMA CORTICOSTERONE IN A SONORAN DESERT MALE SONGBIRD DEVICHE, P.J.; Arizona State University deviche@asu.edu

Changes in baseline and stress-induced plasma corticosterone (CORT) concentrations have been documented in many avian species. However, few studies in intact free-ranging birds have investigated systematic variations of these concentrations throughout the annual cycle and how changes in plasma CORT relate to those of other hormones, particularly gonadal steroids. In adult male Rufous-winged Sparrows, Aimophila carpalis that were sampled in the field over a 1.5 year-long period, baseline plasma CORT changed seasonally. Hormone levels were high during the summer monsoon season (Jul-Sept) when birds were breeding and low during the fall post-breeding molt and throughout the winter non-breeding season. In one year but not the next, plasma CORT was as elevated in March, when males were beginning to develop testes and not yet in breeding condition, as during the summer breeding period. This yearly difference correlated with a difference in local precipitations, indicating that proximate factors associated with these precipitations may stimulate the hypothalamo-pituitary-adrenal axis. Capture and handling for 30 min stimulated CORT secretion. Baseline and stress-induced plasma CORT levels were individually correlated but the amplitude of the stress-induced response did not vary during the annual cycle, suggesting no seasonal change in sensitivity to acute stress. Baseline plasma testosterone (T) was seasonally high during the summer breeding season but low in March, indicating no consistent year-round relationship between the secretion of this hormone and of CORT. In addition acute stress, while increasing plasma CORT, consistently decreased plasma T by almost 50%. The results will be discussed with regards to our current understanding of the functional relationships in birds between the pituitary-adrenal and -gonadal axes.