IUCN Conservation Status Does Not Predict Glucocorticoid Concentrations in Reptiles and Birds

Circulating glucocorticoids (GCs) are the most commonly used biomarkers of stress in wildlife. However, their utility as a tool for identifying and/or managing at-risk species has varied. Here, we took a very broad approach to conservation physiology, asking whether International Union for the Conservation of Nature (IUCN) listing status (concern versus no obvious concern) and/or location within a geographic range (edge versus non-edge) predicted baseline and post-restraint concentrations of corticosterone (CORT) among many species of birds and reptiles. Even though such an approach can be viewed as coarse, we asked in this analysis whether CORT concentrations might be useful to implicate species at risk. Indeed, our effort, relying on HormoneBase, a repository of data on wildlife steroids, complements several other large-scale efforts in this issue to describe and understand GC variation. Using a phylogenetically informed Bayesian approach, we found little evidence that either IUCN status or edge/non-edge location in a geographic distribution were related to GC levels. However, we did confirm patterns described in previous studies, namely that breeding condition and evolutionary relatedness among species predicted some GC variation. Given the broad scope of our work, we are reluctant to conclude that IUCN status and location within a range are unrelated to GC regulation. We encourage future more targeted efforts on GCs in at-risk populations to reveal how factors leading to IUCN listing or the environmental conditions at range edges impact individual performance and fitness, particularly in the mammals, amphibians, and fish species we could not study here because data are currently unavailable.