Under pressure: assessing the influence of hunting on stress and diet quality of boreal bison (Bison bison)

Human activity can impact wildlife with consequences on fitness. For instance, hunting may affect the behaviour and physiology of hunted species. Yet, such impacts are understudied. We examined whether hunting impacted the stress physiology and nutrition of bison (Bison bison). We tested the hypothesis that risk-averse bison had lower quality diets but less stress than those that were accessible to hunters, imposing a tradeoff. We collected fecal samples from areas that received high and low hunting pressure in late winter over two hunting seasons that varied in hunting pressure. We measured fecal glucocorticoid metabolites (FGM) as a measure of stress and fecal nitrogen and other minerals as measures of diet quality. FGM levels did not differ as a function of spatial hunting intensity, but levels were significantly higher in 2018 when hunting rates were over three times greater than in 2019. Concentrations of most major and trace minerals increased in high hunting areas in 2019, coinciding with a sharp decrease in hunter harvest. Taken together, changes in hunting pressure between years may increase stress in bison and limit their access to high quality forage, but the factors at play are difficult to disentangle. To avoid potential tradeoffs between safety and nutrition, wildlife managers could reduce stress and increase nutrition by reducing hunting activity or creating refugia from hunters in high-quality foraging areas, where warranted. More broadly, understanding the sublethal effects that hunting may have on wildlife can help guide management decisions regarding the allocation of hunting pressure on the landscape.