Interactive effects of wildfires, season and predator activity shape mule deer movements

Abstract

Wildfires are increasing in size, frequency and severity due to climate change and fire suppression, but the direct and indirect effects on wildlife remain largely unresolved. Fire removes forest canopy, which can improve forage for ungulates but also reduce snow interception, leading to a deeper snowpack and potentially increased vulnerability to predation in winter. If ungulates exhibit predator‐mediated foraging, burns should generally be selected for in summer to access high‐quality forage and avoided in winter to reduce predation risk in deep snow. Fires also typically increase the amount of deadfall and initiate the growth of dense understory vegetation, creating obstacles that may confer a hunting advantage to stalking predators and a disadvantage to coursing predators. To minimize risk, ungulates may therefore avoid burns when and where stalking predators are most active, and use burns when and where coursing predators are most active. We used telemetry data from GPS‐collared mule deer (Odocoileus hemionus), cougars (Puma concolor) and wolves (Canis lupus) to develop step selection functions to examine how mule deer navigated species‐specific predation risk across a landscape in northern Washington, USA, that has experienced substantial wildfire activity during the past several decades. We considered a diverse array of wildfire impacts, accounting for both the severity of the fire and time since the burn (1–35 years) in our analyses. We observed support for the predator mediating foraging hypothesis: mule deer generally selected for burned areas in summer and avoided burns in winter. In addition, deer increased use of burned areas when and where wolf activity was high and avoided burns when and where cougar use was high in winter, suggesting the hunting mode of resident predators mediated the seasonal response of deer to burns. Deer were not more likely to die by predation in burned than in unburned areas, indicating that they adequately manage fire‐induced changes to predation risk. As fire activity increases with climate change, our findings indicate the impact on ungulates will depend on trade‐offs between enhanced summer forage and functionally reduced winter range, mediated by characteristics of the predator community.

Mammalian resistance to megafire in western U.S. woodland savannas

“…For larger, more mobile species like black‐tailed deer, changes in intensity of use may represent shifts in activity centers, alterations in movement paths, or avoidance of burned areas altogether following wildfire (Jager et al, 2021). As severe fire modifies the structure of vegetation, animals may adjust their navigation of landscapes to minimize risk (Ganz et al, 2022; Kreling et al, 2021) and maximize access to remaining resources (Nimmo et al, 2019). This behavioral response may grant these larger bodied species some level of improved resistance and longer term resilience to quickly leave areas that are recently burned and return when conditions are more favorable.…”

Dynamic energy landscapes of predators and the implications for modifying prey risk

“…Our approach adds to current studies which are starting to consider the more general role of abiotic conditions in altering prey fear landscapes (e.g. Ganz et al., 2022).…”

Movement ecology of an endangered mesopredator in a mining landscape

“…Integrated step selection functions take this further, by including animal movement and resource selection parameters in the model, reducing bias, and allowing further estimation and simulation of habitat selection [ 85 , 110 , 111 ]. For each observed step, we generated five random available steps with turning angles drawn from a von Mises distribution and step lengths drawn from a gamma distribution [ 8 , 86 , 112 , 113 ]. For each observed and random step, we extracted covariates from the four landscape maps at the end of the step.…”