BUSCH, D. S. *; BOYD, E.; WINGFIELD, J. C.; University of Washington, Seattle: Chronic, acute pulses of corticosterone alter body condition and timing of molt

Corticosterone (B) can be detrimental if it is maintained at or close to maximal stress-induced levels. Animals release high levels of B in response to stressful events and modulate the hormone at low levels in other times. Most studies on chronic stress are done with B implants that maintain consistently high levels of plasma B over a period of days. In an effort to design a more ecologically-relevant model of chronic stress, we topically administered B to captive white-crowned sparrows (n=8) in breeding condition for 9 days during a 12 day period. Control animals were administered vehicle (DMSO, n=7) or received no treatment (n=6). Each bird was given 1 treatment 3 times a day, which in B-treated birds resulted in exogenously elevated, though physiologically relevant (25ng/ml), B levels for approximately 3hr per day. Body mass in B-treated birds dropped after initiation of the treatments, but recovered by the 12th day of treatments. Keel muscle score in the B-treated group was low for the duration of the hormone treatments, and recovered by the 6th day after the B treatments ceased. Subcutaneous fat scores were not affected by the B treatments. B-treated birds increased food intake more over time than birds that were unmanipulated. B-treated animals significantly delayed the initiation of post-breeding molt for 15 days. There was no difference in termination of molt among the treatment groups. The changes in body condition of the B-treated animals are similar to those seen in birds given a B implant. Our experimental elevation of B levels was designed to mimic increases in B as occurs in birds frequently exposed to acute stressors. Our results indicate that chronic, acute elevations of B levels may be as harmful to an animal�s health and survival as constant exposure to elevated B levels.