Species-specific movement traits and specialization determine the spatial responses of small mammals towards roads

The barrier effect is a pervasive impact of road networks. For many small mammals individual avoidance responses can be the mechanism behind the barrier effect. However, little attention has been paid to which species and road characteristics modulate road avoidance and mortality risk. We measured the strength of the barrier effect imposed by the road on three rodent species with different body sizes and habitat specializations: Southern water vole (Arvicola sapidus), Mediterranean pine vole (Microtus duodecimcostatus) and Algerian mouse (Mus spretus). We analysed the effect of traffic intensity on use of space and direction of movement and the effect of road type (4-lane highway, 2-lane paved road and 1-lane unpaved road) on crossing rates with simulations of roads bisecting each home range. Finally, we estimated annual mortality risk from collision based on individual speed, crossing rates, body length, traffic volume and road width. Individual mobility and ecological preferences were assumed as two hypotheses to explain species' responses towards roads. The effects were species-specific, with traffic intensity having a negative influence on the use of space and movement directionality only for water voles and with avoidance of paved roads being evident for the Algerian mouse. Road-kill mortality risk was high in pine voles. Habitat specialization, individual mobility and home-range location were identified as important factors of species' responses towards roads. This study draws attention to the role of behaviour and ecological requirements as well as road characteristics on the strength of the barrier effect imposed by roads for different species.