Meeting Abstract

P3.182  Sunday, Jan. 6  Elevated baseline but lowered stress-induced corticosterone titers during courtship display in a lekking bird BACHMAN, GC; GIBSON, RM*; VLECK, CM; Univ. of Nebraska-Lincoln; Univ. of Nebraska-Lincoln; Iowa State University rgibson2@unl.edu

Stress responses of wild birds may be down-regulated if stress-induced re-allocation of energy away from ongoing activities would lower current or future fitness. Well studied contexts include molt, migration, and brood rearing. Energy allocation may also be critical during courtship, particularly if display reduces foraging time and/or elevates energetic expenditure as in lekking species. We investigated the possible modulation of stress responses during courtship in male Sharp-tailed grouse Tympanuchus phasianellus by characterizing sex differences and seasonal variation in the capture-induced stress response. We captured birds on leks using walk-in traps. Birds were bled within 3 min of trap entry and after 30 min for RIA of baseline and stress-induced corticosterone (CORT) titers. In mid-April, during the seasonal peak of female attendance and male display, baseline CORT was significantly higher in males than females whereas stress induced CORT was higher in females than males. Females, but not males, significantly elevated CORT in response to capture. Among males trapped throughout April there was no seasonal trend in baseline CORT, but stress-induced CORT titers exhibited a significant U-shaped relationship with date suggesting a reduced male stress response during the seasonal display peak. Stress-induced CORT was also lower in younger males. In the context of elevated baseline CORT, a lowered stress response could reduce allostatic overload in response to stressors such as frequent inter-male aggression and predator attacks. This interpretation implicates allostatic overload as a cost of sexually-selected lek display.