Characterizing predictors of survival in the American pika (Ochotona princeps)

The measurement of stress hormone (glucocorticoid [GC]) concentration is increasingly used to assess the health of wildlife populations. However, for many species, we do not have a good understanding of the range of GC concentrations that might indicate a compromised individual. A temporary increase in GC concentration can prompt the adoption of behavior or activities to promote individual survival. However, chronic GC elevation results in deleterious effects on health that can reduce survival. In order to use GC concentration as a metric of individual fitness for a given species, it will be necessary to relate individual demographic rates to GC concentration. We related survival in American pikas (Ochotona princeps) to 2 different stress metrics, glucocorticoid metabolite (GCM) concentration in fecal samples and GC concentration in plasma samples. Annual survival was analyzed in relation to each of these stress metrics as well as other physiological metrics and habitat characteristics at several sites in the Rocky Mountains. Among the predictors considered, GCM concentration was by far the strongest predictor of annual survival in pikas, and individuals with higher baseline GCM were less likely to survive. Our metric of flea load was also negatively related to annual survival. Given the limited time and resources that characterize many wildlife conservation projects, it is important to establish which endocrine metrics are the most informative for a species. American pikas have been identified as a sentinel species for detecting effects of climate change, and several correlational studies have projected range contraction for the species. Our results suggest that more mechanistic projections might be possible given further study of the relationship between GCM and climate. Our approach contributes to a better understanding of factors affecting survival in this species and provides a basis for further research relating individual stress response and survival to environmental change.