Apex predators exploit advantageous snow conditions across hunting modes

Apex predators balance functional traits, habitat features, and prey distribution to maximize hunting efficiency. As components of habitat such as snow cover are altered by climate change, functional traits may prove more or less effective given new environmental conditions, with ecosystem-wide impacts as a result of changing predator-prey interactions. Hunting mode is one such functional trait that shapes which environments are best for catching prey. Coursing large carnivores may exploit snow conditions that offer movement advantages, with long chase sequences maximizing their superior mobility over large-bodied ungulate prey that typically sink deeper into snow. However, comparatively little is known about whether stalking predators utilize snow similarly, despite similar theoretical movement advantages over prey. In this study, we examined the effects of snow on two sympatric predators with different hunting strategies: cougars (Puma concolor; stalking predators) and wolves (Canis lupus; coursing predators). We coupled a physically based snow model with kill site investigations and telemetry data from 50 cougars, 14 wolves, 142 mule deer (Odocoileus hemionus), and 90 white-tailed deer (O. virginianus) collected from 2017 to 2021 in Washington state, USA. We first created winter deer distribution models for each year to control for expected prey density. We then generated step selection functions for cougars and wolves using this deer index, snow properties, and other landscape characteristics hypothesized to influence the hunting process. The interaction between snow depth and density shaped both predators' movements and was an unexpectedly strong driver of cougar winter movements and kill site distribution. Wolves weakly selected for shallow (<35 cm), low density (<200 kg/m³) snow, and avoided deeper snow unless sufficiently dense (>350 kg/m³). Cougars selected for very dense (>400 kg/m³), moderate-depth (<50 cm) snow and avoided deep snow. Snow depth and density had similar effects on cougar kill site selection (n = 389 known and probable cougar kills; insufficient sample size for wolves). Our results indicate that snow is a critical component of large carnivore movements regardless of hunting mode. In a warming climate, the knock-on effects of a diminishing snowpack may reduce the hunting success of multiple large carnivore species, consequently altering predator-prey dynamics with cascading ecosystem-wide effects.