Latitudinal gradient in cortisol concentrations in Canada lynx (Lynx canadensis) is not explained by diet

Food limitation is an important stressor for most wildlife, and many specialist consumers will expand their dietary niche to contend with preferred prey limitation. How these dietary responses feed back into stress-axis regulation, however, is unknown. If alternative prey does not sufficiently fill the energetic requirements normally satisfied by preferred resources, then long-term glucocorticoid concentrations could be elevated in individuals consuming alternative prey. We measured cortisol concentrations and stable isotope ratios (δ13C and δ15N) in hair of Canada lynx (Lynx canadensis Kerr, 1792) across their distribution to determine the influence of diet on glucocorticoids while controlling for harvest location. We calculated the Euclidean distance between lynx and regional snowshoe hare (Lepus americanus Erxleben, 1777) stable isotope ratios as an index of diet specialization. We found no relationship between this index and cortisol, suggesting that prey types are interchangeable for lynx in terms of long-term stress axis activation. However, lynx cortisol increased significantly towards the northwestern region of lynx distribution, contrasting with our prediction, and highlighting important considerations for future research. This combination of glucocorticoid and diet analyses suggests that dietary plasticity does not necessarily alter an individual’s experience of potential stressors, despite important implications to population and community dynamics.