96.5 Saturday, Jan. 7 An Investigation of the CORT-Fitness Hypothesis: the Importance of Age and Environmental Quality MADLIGER, C.L.*; LOVE, O.P.; University of Windsor, Ontario; University of Windsor, Ontario firstname.lastname@example.org
Across taxa, measures of baseline stress hormones (eg. corticosterone) are increasingly being utilized as conservation tools for the assessment of individual and/or population condition. To be an effective biomarker in this regard, baseline corticosterone (CORT) levels must show a predictable relationship with fitness. It has been assumed that high levels of baseline CORT are indicative of individuals with low relative fitness, a phenomenon recently coined the CORT-Fitness Hypothesis. However, empirical evidence for this relationship has been largely inconclusive, showing variation both within populations and within individuals across different life history stages. We investigated the relationship between baseline CORT levels and reproductive success in Tree Swallows (Tachycineta bicolor), across two reproductive stages and within the context of habitat quality. We find that individual CORT levels changed from the incubation stage to the nestling provisioning stage, with the direction of change being highly dependent on age. In addition, baseline CORT levels predict fitness only for experienced individuals (those in their second breeding season or later) in high quality habitats and only during the nestling provisioning stage. This is inconsistent with the CORT-Fitness Hypothesis; baseline CORT levels do not show a predictable relationship with reproductive success for all age classes and habitat types. Our results indicate that the relationship between baseline CORT and fitness is context-dependent. Therefore, more information on life history stage, age, and habitat metrics may be necessary to effectively apply stress hormones as relevant physiological indices for conservation.