New research has been published with regard to the impacts that wind turbines may have on bat species in the UK. Whilst the bat fauna in Ireland differs from that found in the UK, this research provides the most relevant information on the situation in Ireland. Previous studies have been carried out in North America and Mainland Europe where bat species composition and ecology differ significantly from that found in Ireland. The Bat Conservation Trust Guidelines are currently being updated to take account of this new research and are likely to be released in the coming months. MKO have reviewed the new data and are applying the findings to the approach taken for upcoming bat surveys and impact assessments.
The research, published by the University of Exeter and funded by Defra UK, was the first study to examine bat interactions with wind turbines in the UK. The primary aim of the study was to investigate if bats are killed at wind turbines in Great Britain and if so, to estimate casualty rates and explore potential risk factors. Researchers carried out fatality searches, using trained sniffer dogs, at forty-six commercial wind farm sites in England, Scotland and Wales, between July and October, from 2011 to 2013 inclusive. In addition, concurrent nightly acoustic surveys were conducted at height, at ground level and at offsite control sites.
The research confirmed bat fatalities at two thirds of all sites surveyed. Estimated casualty rates, which correct for predator and efficiencies, ranged from 0 to 5.25 bats per turbine per month, and 0 to 77 bats per site per month. Species consistently effected included Common pipistrelles and Soprano pipistrelles, species that are also widespread in Ireland, as well as Noctule bats, which do not occur in Ireland. Only single casualties of other bat species were recorded. Factors that increased the risk of bat mortality included larger rotors sizes and greater numbers of turbines. However, no relationship was found with fatalities and nacelle height.
Similar to previous studies, the greatest bat fatalities occurred on nights with low wind speeds and high night-time temperatures. The authors concluded that curtailing turbines would be extremely effective in minimising bat collisions. However, within the current study, bat fatalities only occurred on 3.6% of nights suitable for curtailing and therefore, the authors recommend post-construction monitoring to confirm casualties before implementing any curtailment strategies. In addition, they recommend blade feathering to restrict blade rotation below cut-in speed.
Acoustic recordings made at ground level and nacelle gave different estimates of activity, with ground-level recordings underestimating activity within the ‘at risk’ zone of the rotor sweep area. In addition, recorded bat activity was highly variable day to day and the authors recommend much longer monitoring periods than those currently employed in pre-construction surveys.
Ireland’s bat fauna differs considerably in species and behaviour to those of mainland Europe. However, more similarities exist between Ireland and the UK, making this the most relevant research to Irish bats, published to date. In response to this new research, guidelines published by Bat Conservation Trust on surveying bats and wind farms, which are widely implemented in Ireland, will be updated in the coming months.