Research conducted in Europe last year indicated that higher flying bats, notably the Nyctalus and Pipestrellus species, appear to suffer the largest number of turbine fatalities, the majority of which occurred during late summer. It is possible that such fatalities are linked to migratory flights at the start of the migrating season.
Clearly, further research is needed. The national project on bats and wind turbines in the UK, funded by the environment ministry, is looking at the effect of wind farms on different species of bats. The project will investigate the value of pre-construction acoustic surveys and seek to identify the most effective mitigation methods. In the US, the Bat and Wind Energy Cooperative has a research budget of more than $4 million and has brought together representatives from Bat Conservation International, the US Federal Government's Fish and Wildlife Service, the American Wind Energy Association and the US Department of Energy.
With research under way on more than one continent our understanding of wind farms' impacts on bat species should improve - as should our options for reducing these impacts. Already there is legislation in many countries that allows impacts on bats to be considered. Most sizeable wind projects in Europe are subject to an environmental impact assessment (EIA). In England and Wales any development of two or more turbines, or where the structure exceeds 15 metres in height, is assessed for its potential environmental impacts, including those on valued ecological receptors such as bat populations.
As part of an EIA, ecological consultants need to assess impacts using the best available evidence, combined with their collective experience and professional opinion. Good baseline information on the bats in and around a wind farm site is necessary.
Any assessment should draw on the latest research and guidelines. In the UK, guidelines published by the Bat Conservation Trust have built on those from the Agreement on the Conservation of Populations of European bats - known as Eurobats. The guidelines are quite specific and require extensive preand post-development surveys, including a desk study of up to 10 kilometres from a site boundary, activity surveys across the whole site and roost surveys. Regulators are more likely to accept results from surveys that closely follow these guidelines.
Good baseline ecological data can help identify which sites are less likely to have an impact on bats, as well as the best location and configuration of wind turbines within a selected site. Greater survey effort will often ensure fewer problems at a later stage.
The effect of wind turbines on bats will always depend on a number of site-specific factors. These include the bat species that are present, their numbers, roosting opportunities, the habitat and landscape, and existing environmental conditions. Good practice at the survey stage can set the stage for solutions that will minimise impacts, including fatalities.
Richard Arnold is technical director at specialist ecological consultancy Thomson Ecology. For more details, go to www.thomsonecology.com