Wolf presence disrupts seasonal variation in hair cortisol among free-ranging beef cattle

Free-ranging livestock face increasing exposure to recovering carnivore
populations, yet the physiological consequences of predator reintroduction
remain poorly understood. Here, we examined hair cortisol concentrations
in beef cattle from nine herds across California's Sierra Nevada to
assess how wolf presence affects stress physiology over seasonal
transitions. We collected hair samples before and after summer grazing
periods, comparing herds exposed to the Lassen Wolf Pack with unexposed
herds across a natural temperature gradient. Using Bayesian multilevel
regression models, we tested for effects of wolf presence and found that
hair cortisol concentrations decreased with increasing minimum
temperatures (13.5% reduction per 1°C increase), but this relationship was
disrupted in wolf-exposed herds. We also found that wolf presence
moderated the cortisol-temperature relationship, with wolf-exposed herds
showing inverted patterns during summer compared to unexposed herds. These
results suggest that wolf presence disrupts normal physiological
regulation rather than simply elevating hair cortisol concentrations,
suggesting dysregulation indicative of sustained allostatic load in
wolf-naïve cattle populations. Our findings demonstrate that predator
reintroduction can fundamentally alter livestock physiology indirectly via
metabolic regulation, with implications for animal welfare, productivity,
and carnivore-livestock coexistence strategies in working landscapes.