Snow sinking depth and forest canopy drive winter resource selection more than supplemental feeding in an alpine population of roe deer

In alpine environments, snow typically reduces the accessibility of herbivores to food during winter and may hamper survival in those species with poor adaptation to move in deep snow. Supplemental feeding systems compensate for food limitation, but modify resource distribution and potentially affect individual space use. We investigated the importance of snow cover and supplemental feeding in shaping winter habitat use and selection of the European roe deer (Capreolus capreolus), a small deer species not specifically adapted to snow. We applied a used/available experimental design to assess the effects of snow cover on roe deer distribution at a fine scale and compared this approach with remotely sensed satellite data, available at moderate spatial resolution (snow MODIS). Based on this, we developed a resource selection function. We found a strong selection for habitat spots covered by forest where snow sinking depth was less pronounced, likely providing thermal and hiding protection on the one side and minimising the effect of snow on locomotion on the other. Roe deer showed only a minor preference for sites in proximity to feeding stations, possibly compensating the costs of access to these sites by means of a ‘trail-making’ behaviour. Snow cover assessed by moderate resolution satellite was not proportional to roe deer probability of use, highlighting the importance of local information on snow quality and distribution to complement remotely sensed data.