The effect of wind turbines on bats in Britain
Richardson, Suzanne Mary
Thesis or dissertation
University of Exeter
Reason for embargo
The thesis contains sensitive information on the impact of wind turbines on bats that could potentially have implications for the operation of major industry, and in which the media is likely to be interested. This PhD was conducted within a wider project, and we are under an obligation to the funders to ensure that all data remain out of the public domain until Defra publish the final report on the project (anticipated early 2016, but which could potentially be delayed for several months by government ministers). The project as a whole is under a high level of public scrutiny, and the temporary embargo would also assist in ensuring that all of her papers are submitted for publication before the thesis is released.
The increase in wind energy production has been relatively rapid and is expected to continue at a global scale. However, numbers of bat carcasses found at wind turbines in North America in the early 21st century raised concern about the plight of this taxon with the growth in wind-energy generation. This led to carcass searches for bats becoming commonplace at wind farms globally. However, few large scale systematic studies have assessed the effects of wind turbines on bats, especially for species considered potentially at higher risk in Europe. In this thesis the number and species of bats killed from wind farms were estimated across Britain, and the important predictors (i.e. activity, turbine characteristics and habitat) of fatality were determined. Insect abundance, biomass and bat activity was also quantified at turbine and control locations, to assess if insects and hence bats were attracted to turbines. In addition, assessments were made of the effects of increasing temporal and spatial replication of acoustic monitoring on estimates of species composition and bat activity. This was assessed for activity monitored at ground and at the centre of the rotor sweep area (the nacelle). Carcass searches were conducted using trained search dogs and concurrently bats were surveyed acoustically at three randomly selected turbines at ground and from the nacelle at 48 wind farms throughout Britain. Bats were also monitored acoustically at paired controls (with a randomly selected turbine) at 20 of the wind farms sites. In addition, nocturnal Diptera were sampled at 18 of the sites using a paired turbine and control design. Across 139 wind turbines, 188,335 bat passes were recorded and 2,973 carcass searches performed. Edge and open aerial foraging species, in particular Pipistrellus pipistrellus and P. pygmaeus were most at risk of fatality 4 at wind farms in Britain. The number of Pipistrellus pipistrellus killed annually in Britain between mid-July and mid-October was estimated at 2,373 95% CI 513 to 4,233 and the number of P. pygmaeus at 3,082 95% CI 1,270 to 4,894. When compared to population estimates, the number of Pipistrellus pygmaeus killed was 57% higher than the number of P. pipistrellus killed (0.19% of the population versus 0.43%, respectively). This may be due to Pipistrellus pygmaeus flying more often within the rotor sweep area compared to P. pipistrellus. Activity measured at the nacelle, which is generally assumed to be a better predictor of fatalities, was not a significant predictor of the probability of a fatality for all species combined, Pipistrellus pipistrellus, or P. pygmaeus. Pipistrellus pipistrellus activity and P. pygmaeus activity, measured at ground level were not good predictors of their respective fatalities. Whilst there was some evidence that Pipistrellus pipistrellus and P. pygmaeus activity monitored at ground level, was a significant predictor of the probability of their respective fatalities occurring, across wide ranging turbine types, fatality estimates were large. This is presumably due to the importance of turbine characterises (the wind speed that turbines become operational (cut-in speeds) turbine and the distance between the ground and blade tip at the bottom of the rotor sweep area) both being important negative predictors of fatalities for Pipistrellus pipistrellus. Predicting from models, if the cut-in speed is increased from 3.5 to 5 m s-1 the number of Pipistrellus pipistrellus fatalities would be reduced by 76% (0.23 fatalities per turbine per month to 0.06). These findings have important implications for guidance, since activity is the ubiquitous measure used to assess fatality risk for all species. Since, Pipistrellus pipistrellus and P. pygmaeus were detected at 98% and 92% of sites respectively; it could be 5 assumed that these species would be detected at the majority of wind farms within their range. Therefore, in a British context, curtailing wind turbines below 5 m s-1 could be an effective mitigation strategy without the costly requirement to monitor activity. Pipistrellus pipistrellus and P. pygmaeus activity was 46% (6.3 ± 1.3 SE mean passes per night c.f. 3.4 ± 1.3 SE) and 34% (4.0 ± 1.4 SE c.f. 2.7 ± 1.4 SE) higher at turbines compared to controls, respectively. Given that habitat and elevation were consistent between paired turbines and controls and monitoring was conducted on the same nights, higher activity at turbines compared to controls provides evidence that these two species are attracted to wind turbines. Furthermore, since the biomass of nocturnal Diptera, the main insect prey for Pipistrellus spp., was higher at controls compared to turbines, and bat foraging at turbines was not predicted by insect abundance or biomass, attraction is unlikely to be due to insects. Evidence presented here shows that bats are attracted to turbines, and therefore measuring activity at pre-construction sites for environmental impact assessments is unlikely to be effective. In conclusion, these results provide further evidence that common species are killed but generally in relatively low numbers, they also support the view that monitoring activity for assessing fatality risk at wind farms is ineffective. It is imperative that wind energy is developed using an evidence based approach. However, it also important that wind energy continues to contribute to an increasing renewable energy sector. In conclusion, results presented here, support that wind turbines are likely to be having a small impact on bat populations in Britain.
Department for Environment, Food and Rural Affairs, Department of Energy & Climate Change, Natural England, Natural Resources Wales, Scottish Natural Heritage, and RenewableUK
Mathews, Prof. Fiona
Hosken, Prof. David
PhD in Biological Sciences