Impacts of frequent, acute pulses of corticosterone on condition and behavior of Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii).

Little is known about how frequent, acute stressors affect wild animals. We present two experiments conducted on captive, Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii) that explore how frequent, acute doses of corticosterone (CORT) affect condition and behavior. CORT was administered either once or three times a day to birds in pre-breeding, early-breeding, or late-breeding life-history stages. Two additional groups were included to control for the CORT delivery vehicle, DMSO, and the treatment process. Our results indicate that CORT treatment decreases condition, but that its effects are dependent on frequency and life stage. Specifically, CORT-treated birds delayed the onset of molt and had reduced body mass, flight muscle, and food consumption. CORT treatment did not affect fat stores, bile retention in the gallbladder, or the expression of migratory restlessness behavior. These results increase our understanding of the effects of frequent, acute stressors and the development of chronic stress states.