Factors affecting the permeability of road mitigation measures to the movement of small mammals

Abstract

Mitigation measures, such as wildlife-exclusion fencing and crossing structures (overpasses, underpasses, culverts), have been widely demonstrated to reduce the negative effects of roads on medium-sized and large animals. It is unclear how these mitigation measures influence the movement of small mammals (<5 kg). Our study has three objectives: (1) to test whether culverts improve highway permeability; (2) to determine factors associated with culvert use, such as culvert obstruction by snow; (3) to evaluate factors contributing towards fence permeability, such as the presence of a culvert, snow depth, and fence mesh size. We used snow tracking to assess the movement for four small-mammal taxa along the Trans-Canada Highway corridor in Banff National Park, Alberta, Canada. We found that the presence of a culvert within 100 m of transects significantly improved fence and highway permeability. Obstruction of the culvert entrance by snow was negatively correlated with the probability of use, and therefore, of highway permeability. Furthermore, the mesh size of the fencing did not affect fence or highway permeability. We recommend that culvert entrances be located on the outside of fenced right-of-ways to reduce obstruction by highway maintenance activities such as snowplowing.