Stress hormone metabolites predict overwinter survival in yellow-bellied marmots

Biological assays of stress, in particular noninvasive measures, are valuable tools for wildlife management. Chronic stress can have negative impacts on fitness outcomes, and an area of particular interest is if elevated baseline stress levels are predictive of survival outcomes. We examined the relationship between fecal glucocorticoid metabolites (FGMs) measured from samples collected during routine trapping and overwinter survival in a wild population of yellow-bellied marmots (Marmota flaviventris). In particular, we asked if elevated FGMs were associated with reduced survival probability. Both higher yearly FGM levels averaged over several months and higher late season FGM levels averaged over the several weeks before hibernation were associated with lower probability of survival. Additionally, there was an interaction between late-season FGM levels and body mass, such that the association between late-season FGMs and survival was much stronger in animals with lower body mass (i.e., in poorer condition). This study highlights the promise of using stress hormone metabolites, a noninvasive measure, for studying factors affecting survival in this and potentially other natural wildlife systems.