The research project involved developing the use of acoustic deterrents as part of a bat mitigation strategy for the proposed new HS2 rail line. Research was initiated to investigate whether it was feasible to use high frequency noise to deter woodland bats, and in particular Bechstein’s bat, from sensitive areas of the rail corridor, with the aim of keeping bats away from potential collision with trains. The project was a collaborative effort with technical specialists from The Ecology Consultancy, Temple Group, The University of Bristol and HS2 Ltd.
Acoustic Deterrents as a Bat Mitigation Strategy
The team pooled their collective knowledge, experience and expertise to devise and implement a scientifically robust study programme to identify and quantify the impact and effectiveness of high frequency noise on bats. Noise deterrents were selected as a potential mitigation method because in recent years acoustic deterrents have been investigated to displace bats from churches and the air space around wind turbines.
Deaton Acoustic units were used to generate the noise output, and bat behaviour with and without noise was recorded using thermal imaging cameras, infra red cameras and teams of surveyors at fixed distances from the noise source. Heat sources attached to poles at different heights and distances provided markers visible to the thermal imaging cameras which enabled more accurate recording of the distances and heights at which bats were flying. A programme of survey replicated throughout the active season was implemented over two study years The first year of study demonstrated effective deterrence distances for pipistrelles, but further data for Myotis species was required to provide robust data for statistical analysis. It was also important to understand if the noise was directional and if not, what degree of noise spillage was occurring and whether this would result in unwanted displacement of bats. A second season of study and detailed analysis of acoustic data by Temple noise consultants provided greater confidence in the findings and the conclusions drawn about the effectiveness of this technique. A good understanding of the noise dispersal pattern and the effective distance enabled us to assess and adapt the sound emitted by acoustic deterrents to maximise their effectiveness in prompting localised and predictable changes in bat flight behaviour.
The study demonstrated that acoustic could be used to enhance the effectiveness of mitigation measures proposed along parts of the HS2 line, and could potentially be used to divert bats from former flight paths onto new flight lines linked to green bridges or underpasses
The work was recognised at the annual awards ceremony of the Association of Noise Consultants in 2019, winning both the Innovation Award and being joint winner of the Environmental Acoustics in Infrastructure Award