Adrenocortical sensitivity to stress in Dark-eyed Juncos(Junco hyemalis oregonus)breeding in low and high elevation habitat

We compared the adrenocortical stress responses of a songbird, the Dark-eyed Junco, across a steep elevation gradient. Concentrations of the stress hormone corticosterone were compared at 3, 30, and 60 minutes after exposure to a standardized stressor in juncos breeding in low- (1,000 m a.s.l.) versus high- (2,000 m a.s.l.) elevation habitat in Jasper National Park, Alberta, Canada. Baseline corticosterone (3 minutes post-capture) in juncos did not differ between elevations. Stress-induced corticosterone in juncos did not differ markedly between elevations during the initial stage of the stress response (30 minutes post-capture). However, by 60 minutes post-capture, corticosterone was higher at low elevations, but with borderline statistical significance. Females had a lower adrenocortical response to stress than males, and breeding individuals had a lower response to stress than non-breeders. The influence of gender and breeding stage may correspond to an interaction between testosterone and corticosterone.