Yearly Variations in GCM Concentrations in Female Mountain Hares (Lepus timidus) and the Effect of Pregnancy

SIMPLE SUMMARY: The measurement of stress hormones has become a widely used and effective tool for evaluating adrenocortical activity in animals. However, to correctly interpret stress measurements, the potential sampling bias resulting from an oversampling of individuals in different states of pregnancy has rarely been investigated. We found significant yearly variations in states of pregnancy, which is related to the conditions of the females due to the snow cover duration before and at the start of the reproductive period. These results are important for improving the interpretation of stress hormone concentrations in free-ranging populations during the breeding and reproductive periods. ABSTRACT: The measurement of glucocorticoid metabolites (GCMs) in faeces has become a widely used and effective tool for evaluating the amount of stress experienced by animals. However, the potential sampling bias resulting from an oversampling of individuals in different states of pregnancy has rarely been investigated. In this study, we validate a noninvasive method for measuring gestagen metabolites in female mountain hares (Lepus timidus) under controlled conditions. We also measured the concentration of gestagen metabolites of females in a free-ranging population during the early breeding and post-breeding periods from 2014 to 2019. We found significant yearly variations in gestagen metabolites, which were related to the condition of the females due to the snow cover duration before and at the start of the reproduction period. GCMs were significantly influenced by the gestagen metabolite levels. These results are important for improving the interpretation of GCM concentrations in free-ranging populations during the breeding and reproductive periods.