Effects of season, sex, and sample collection on concentrations of fecal cortisol metabolites in red deer (Cervus elaphus).

Seasonal variation, sex differences, and invasive sample collection may confound glucocorticoid measures as indices of stress. We investigated the effects of sex and season on glucocorticoid production on a non-invasive basis by measuring concentrations of cortisol metabolites in feces of undisturbed red deer (Cervus elaphus). Although feces can be collected easily, assignment to individuals is difficult. Anonymous fecal samples may cause overrepresentation of particular individuals thus introducing a source of error when estimating mean hormone levels within a population. We therefore examined the effects of collecting anonymous fecal samples on mean fecal cortisol metabolite levels. Neither sex nor sample collection mode significantly affected mean fecal cortisol metabolite concentrations in the studied population of red deer. Fecal glucocorticoid excretion varied seasonally with a peak during December and January. Out of several potential predictor variables investigated, minimum ambient temperature and snow proved to be the only factors exerting a significant effect on fecal glucocorticoid excretion. We suggest that high winter glucocorticoid levels may act via catabolic function during adaptation of deer to cold winter month when resources are limited.