Deer density drives habitat use of establishing wolves in the Western European Alps.
The return of top carnivores to their historical range triggers conflicts with the interests of different stakeholder groups. Anticipating such conflicts is key to appropriate conservation management, which calls for reliable spatial predictions of future carnivore occurrence. Previous models have assessed general habitat suitability for wolves, but the factors driving the settlement of dispersing individuals remain ill-understood. In particular, little attention has been paid to the role of prey availability in the recolonization process. High spatial resolution and area-wide relative densities of the wolf's main ungulate prey species (red deer, roe deer and chamois) were assessed from snow-track surveys and modelled along with wolf presence data and other environmental descriptors to identify the main drivers of habitat selection of re-establishing wolves in the Western European Alps. Prey species abundance was estimated from the minimum number of individuals recorded from snow-tracks along two hundred and eighteen 1-km transects surveyed twice a year during four successive winters (2012/2013-2015/2016). Abundance estimates per transect, corrected for species-specific detection probabilities and averaged across winters, were used to model area-wide relative prey density and biomass. Confirmed wolf observations during the same four winters were used to develop a spatially explicit habitat selection model for establishing wolves, based on our estimates of prey supply and other environmental descriptors of topography, land-use and climate. Detection-corrected ungulate prey abundances and modelled relative densities varied considerably in space (0-2.8, 1.3-4.5 and 0-6.3 per 50 ha in red deer, roe deer and chamois respectively; 1.3-11.65 pooled), while total predicted prey biomass ranged from 23 to 304 kg per 50 ha. Red deer density was the most important factor explaining wolf occurrence (31% contribution), followed by roe deer density (22%), winter precipitation (19%) and presence of game reserves (16%), showing that food supply, especially red deer as the most profitable prey in the Western Alps, was the main driver of winter habitat selection during the settlement phase. Synthesis and applications. We demonstrate the crucial importance of including accurate, fine-grained information about prey supply for predicting recolonization patterns of carnivores and thus anticipating areas with potential human-wildlife conflicts where preventive measures should be prioritized.