1. It is well known that roads can have a significant impact, usually negative, on species and ecosystems. However, despite their protected status in many countries, little research has been done into the effects of roads on bats. With a view to making more informed management recommendations, we address the simple question: are bat activity and diversity (as measured with ultrasonic detectors) correlated with distance from a major road?
2. Broadband acoustic surveys were conducted on 20 walked transects perpendicular to the M6, a major road in Cumbria (UK), with bat activity recorded at eight spot checks per transect at different distances from the road. Climatic and habitat variables were also recorded, and the relationships between bat activity and these variables were investigated using generalised estimated equations (GEE) and ordinal logistic regression.
3. Total bat activity, the number of species and the activity of Pipistrellus pipistrellus (the most abundant species) were all positively correlated with distance from the road. Total activity increased more than threefold between 0 and 1600 m from the road. These effects were found to be consistent over 2 years.
4. Synthesis and applications. This study is one of the first to show that roads have a major negative impact on bat foraging activity and diversity and is broadly applicable to insectivorous bat communities worldwide. Mitigation requires that roads are made more permeable to bats through the use of effective crossings, such as underpasses and overpasses, and that habitat is improved within 1 km of major roads. Because the effectiveness of current mitigation measures is unknown, well-designed monitoring of mitigation is essential.