How do bats use waterways?
Bats often roost along waterways, using bridges, culverts, waterside buildings and trees for rest, shelter and protection. Waterways, particularly those with bankside vegetation, are a rich source of insect food for bats and form a well-connected network for bats commuting through the landscape.
Daubenton’s bat is also known as the Water Bat; it flies parallel to the surface of the water catching insects as they emerge with its feet. For populations trends for Daubenton’s bat see our latest NBMP report. Most of the UK’s other bat species also use watercourses either for roosting, commuting or foraging.
How can bats be impacted by development along watercourses?
Where development and maintenance occurs alongside watercourses bats can be impacted through damage or destruction of roosts, for example if gaps in bridges or culverts are filled, buildings demolished or trees felled or lopped.
Commuting and foraging bats can also be impacted through loss of bankside vegetation or lighting of the watercourse. Even naturalising rivers by removing weirs could alter the flow regime and affect foraging bats.
How can bats using watercourses be protected through planning?
All work that could impact bats should be subject to an ecological impact assessment by a qualified ecological consultant as early as possible to comply with the relevant legislation and national/local planning policy. Survey work should follow industry standards.
For consideration of roosts in culverts, BCT and the Environment Agency have designed a survey form, with the aim of standardising data collection and enabling a greater understanding of the types of culverts used by bats.
The mitigation hierarchy (avoid first, then mitigate next, then compensate as a last resort) should be applied. If impacts on roosts cannot be avoided, a European Protected Species licence may be required for works to go ahead legally. Where work requires planning permission the Local Planning Authority may need to consider the three derogation tests (public interest, no satisfactory alternative and maintaining favourable conservation status) and apply appropriate conditions to any planning permissions. An example of bat roost mitigation work undertaken on a culvert containing a Daubenton's maternity roost was presented at the mitigation case studies forum 2017 and is recorded in the proceedings document (page 20).
All developments should consider impacts on bat habitats, including changes in the flow regime of a waterway and alterations to bankside vegetation
Developments should also consider the impact of lighting on bats; see our guidance on Bats and Artificial Lighting. Useful guidance is also available in Bath and North-East Somerset Council’s supplementary planning guidance: Protecting Bats in Waterside Development.
How can watercourses be enhanced through planning?
Enhancements are also required through relevant planning policy; roosts can be proactively built into buildings or bridges and bankside planting deployed to improve connectivity and foraging habitats, contributing to biodiversity net gain.