Environmental Stress in New England Cottontails (Sylvilagus transitionalis) Is Mitigated by High-Quality Habitat.

Organisms in changing environments are subjected to environmental perturbations that may exacerbate physiological stress. Under the Cort-Fitness Hypothesis framework, sustained elevations in physiological stress can negatively impact individual fitness. This hypothesis predicts a positive association between stressors and glucocorticoids. Using fecal glucocorticoid metabolite (FGM) concentrations from non-invasively collected fecal pellets, we assessed how physiological condition of an imperiled mammal, the New England cottontail (Sylvilagus transitionalis), correlates with potential stressors, namely a proxy of habitat quality (forest successional stage), the presence of a nonnative competitor (eastern cottontail, Sylvilagus floridanus), and the density of an invasive plant species (Japanese barberry, Barberis thunbergii). Invasive plant prevalence and eastern cottontail presence independently had small effect sizes. Additionally, there was an interaction effect of eastern cottontail prevalence and Japanese barberry stem density on FGM concentrations, wherein increasing barberry stem density was associated with reduced FGM concentrations in patches with high eastern cottontail prevalence. Consequently, use of high-density Japanese barberry by New England cottontails may ameliorate physiological stress where eastern cottontails are prevalent. It follows that preferred patches, such as those with abundant food resources and cover, may reduce the physiological stress associated with competition and habitat degradation.