The construction of roads has the potential to negatively impact bat populations, through loss of roosts, foraging habitats and by severing landscape elements used as commuting routes by bats. Roads create an open space, which most bat species are reluctant to cross. Traffic further increases the barrier effect due to sudden movement, noise, headlamps, street lighting and the risk of collision. Most species of bat fly relatively close to the ground or close to trees and hedges for protection against the weather and potential predators. Those that do cross roads typically do so at traffic height, with a high risk of collision. Research shows that roads also have a major negative impact on bat foraging activity and diversity.
Bats are afforded protection by European and UK law in an effort to help bat populations recover from the devastating losses sustained in the last century. Mitigation for the impacts of roads is therefore an essential part of helping to ensure the survival of our bat species.
Eco-passages in the form of different types of under-passes (tunnels and culverts) and overpasses (hop-overs, elevated verges and green bridges) are important for providing safe crossing points for all types of wildlife, including bats. The effectiveness of such schemes in helping biodiversity should be robustly monitored, pre and post-construction, to enhance the design of future mitigation.
Wire or mesh structures placed at height over roads, known as bat gantries or bat bridges, have been proposed as artificial road crossing structures for bats and have been erected as mitigation over many roads in the UK and Europe. However, one recent study in the north of England has demonstrated the ineffectiveness of such structures because at the sites investigated the bats still crossed the road at the height of the oncoming traffic.
We are keen to see further pre- and post-construction monitoring and research across the UK and Europe to consolidate knowledge on what constitutes effective mitigation for the fragmentation of commuting routes by roads. We would encourage more investigation of natural crossing points such as hop-overs, elevated verges and green bridges (also known as land or habitat bridges) that could deliver a benefit for the bat species involved, and also for other species impacted by such developments. This is an approach often used in Europe where the use of ‘green bridges’ is more widely adopted. The effectiveness of such schemes in helping biodiversity should be properly monitored to enhance the design of future mitigation in the UK.