Individual study: Effectiveness of mitigation of the impacts of a new road on horseshoe bats Rhinolophus ferrumequinum in Wales, UK
Davies J.G. (2019) Effectiveness of mitigation of the impacts of a new road on horseshoe bats Rhinolophus ferrumequinum in Wales, UK. Conservation Evidence, 16, 17-23
The intervention described in this paper was designed to allow greater horseshoe bats Rhinolophus ferrumequinum to cross safely underneath a newly constructed road scheme in Pembrokeshire, Wales. The mitigation measures, consisting of bridges, culverts and underpasses, were designed and positioned to increase the likelihood that they would be used by bats. These features were then monitored to determine their effectiveness from the proportion of bats flying safely through the mitigation compared to over the carriageway. This was done using a combination of bat surveyors with hand-held detectors and night-vision equipment, and automated bat detectors. Effectiveness of the different mitigation features increased with increasing cross-sectional area, with a culvert of 1500 mm diameter used less frequently than a larger culvert of 1800 mm x 3000 mm. The larger mitigation measures were generally more than 85% effective. Position in the landscape and the presence of features to guide bats into the mitigation are also likely to be important. In order to assess the likely impacts of a new road scheme on a designated bat population this study also considers local bat population trends, the time of night when most bats cross the road and approximate traffic volumes at these times.