The effect of roads on bats in the UK: a model for evidence based conservation

Despite their protected status, little research has been done into the effects of roads on bats or the effectiveness of current mitigation practice. We conducted broadband acoustic surveys on 20 walked transects perpendicular to two major roads in the UK, the M6 in Cumbria, and the M5 in Somerset. Bat activity and habitat variables were recorded at different distances from the road, and the relationship between these variables were investigated using generalised estimated equations (GEE), and ordinal logistic regression. Total bat activity and the activity of Pipistrellus pipistrellus (the most abundant species) were positively correlated with distance from both roads, although the magnitude of the effect was greater by the M6. Distance from the road was positively correlated with the number of bat species by the M6 only. Higher quality habitat surrounding the M5 may have reduced the negative road impacts. The use of direct sampling to collect acoustic data revealed a greater road effect than time expansion methods, which is likely due to increased accuracy through continuous sampling and a larger dataset. Three underpasses and four wire bat gantries were investigated in northern England using echolocation call recordings and observations. The bat gantries were ineffective and used by a very small proportion of bats. Only one underpass located on a pre-construction commuting route could be considered to be effective, and attempts to divert bats were unsuccessful. Further research should focus on crossing structures built on original bat commuting routes, such as underpasses and green bridges. We suggest an integrated approach to mitigation, combining crossing structures and habitat improvements. New crossing structures need to be developed and tested, given the poor success of current structures. Robust pre- and post-construction monitoring using a standardised methodology is essential to assess the effectiveness of mitigation schemes and build an evidence-base for successful conservation.