Environmental assessments are routinely carried out for wind farm proposals, and potential impacts on the local environment (e.g. plants, animals, soils) are evaluated. Turbine locations and operations are often modified as part of the approval process to avoid or minimise impacts on threatened species and their habitats. Any unavoidable impacts can be offset with conservation improvements of similar ecosystems which are unaffected by the proposal.
Projects such as the Black Law Wind Farm have received wide recognition for its contribution to environmental objectives, including praise from the Royal Society for the Protection of Birds, who describe the scheme as both improving the landscape of a derelict opencast mining site and also benefiting a range of wildlife in the area, with an extensive habitat management projects covering over 14 square kilometres.
A research agenda from a coalition of researchers from universities, industry, and government, supported by the Atkinson Center for a Sustainable Future, suggests modeling the spatiotemporal patterns of migratory and residential wildlife with respect to geographic features and weather, to provide a basis for science-based decisions about where to site new wind projects. More specifically, it suggests:
- Use existing data on migratory and other movements of wildlife to develop predictive models of risk.
- Use new and emerging technologies, including radar, acoustics, and thermal imaging, to fill gaps in knowledge of wildlife movements.
- Identify specific species or sets of species most at risk in areas of high potential wind resoures.
Birds
A study estimates that wind farms are responsible for 0.3 to 0.4 fatalities per gigawatt-hour (GWh) of electricity while fossil-fueled power stations are responsible for about 5.2 fatalities per GWh. The study therefore states that fossil fuel based electricity causes about 10 times more fatalities than wind farm based electricity, primarily due to habitat alteration from pollution and mountain-top removal for coal mining. In Denmark, where wind turbines generate 9% of electricity, wind turbines kill about 30,000 birds per year. In the United States, the U.S. Fish and Wildlife Service estimated in 2009, that turbines kill 440,000 birds per year, though mortality is expected to increase significantly as wind power generation expands by 2030 to levels about 12 times higher than 2009 levels. In comparison, 80,000 birds are killed by aircraft, and 500 million killed by cats every year. Even greater numbers of bird deaths are attributed to collisions with buildings. Other studies have stated that 57 million are killed by cars, 97.5 million killed by collisions with plate glass, and hundreds of millions killed by cats. An article in Nature stated that each wind turbine kills an average of 4.27 birds per year.
In the UK, the Royal Society for the Protection of Birds (RSPB) concluded that “The available evidence suggests that appropriately positioned wind farms do not pose a significant hazard for birds.” It notes that climate change poses a much more significant threat to wildlife, and therefore supports wind farms and other forms of renewable energy. In 2009 the RSPB warned that “numbers of several breeding birds of high conservation concern are reduced close to wind turbines,” probably because “birds may use areas close to the turbines less often than would be expected, potentially reducing the carrying capacity of an area.” The National Audubon Society in the U.S. takes a similar position, broadly supporting wind power to help mitigate global warming, while cautioning against siting wind farms in areas especially important to birds and other affected wildlife.
Concerns have been expressed that wind turbines at Smøla in Norway are having a deleterious effect on the population of White-tailed Eagles, Europe’s largest bird of prey. They have been the subject of an extensive re-introduction programme in Scotland, which could be jeopardised by the expansion of wind turbines.
The Peñascal Wind Power Project in Texas is located in the middle of a major bird migration route, and the wind farm uses avian radar originally developed for NASA and the United States Air Force to detect birds as far as four miles away. If the system determines that the birds are in danger of running into the rotating blades, it shuts down the turbines. The system automatically restarts the turbines when the birds have passed.
At the Altamont Pass Wind Farm in California, a settlement has been reached between the Audubon Society, Californians for Renewable Energy and NextEra Energy Resources (who operate some 5,000 turbines in the area). Nearly half of the smaller turbines will be replaced by newer, more bird-friendly models. The project is expected to be complete by 2015 and includes $2.5 million for raptor habitat restoration.
Some paths of bird migration, particularly for birds that fly by night, are unknown. A study suggests that migrating birds may avoid the large turbines, at least in the low-wind non-twilight conditions studied. A Danish 2005 study showed that radio tagged migrating birds traveled around offshore wind farms. Less than 1% of migrating birds passing an offshore wind farm in Rønde, Denmark, got close to collision, though the site was studied only during low-wind non-twilight conditions.
Bats
Bats may be injured by direct impact with turbine blades, towers, or transmission lines. Recent research shows that bats may also be killed when suddenly passing through a low air pressure region surrounding the turbine blade tips.
The numbers of bats killed by existing onshore and near-shore facilities has troubled bat enthusiasts. A study in 2004 estimated that over 2,200 bats were killed by 63 onshore turbines in just six weeks at two sites in the eastern U.S. This study suggests some onshore and near-shore sites may be particularly hazardous to local bat populations and more research is needed. Migratory bat species appear to be particularly at risk, especially during key movement periods (spring and more importantly in fall). Lasiurines such as the hoary bat, red bat, and the silver-haired bat appear to be most vulnerable at North American sites. Almost nothing is known about current populations of these species and the impact on bat numbers as a result of mortality at windpower locations. It has been suggested that bats are attracted to these structures in search of roosts. Offshore wind sites 10 km or more from shore do not interact with bat populations.
Scientists at the U.S. Geological Survey have already conducted research using stable isotope analysis to track migration among terrestrial mammals. USGS scientists are currently applying this technique in their efforts to figure out the geographic origins of bats killed by wind turbines.
In April 2009 the Bats and Wind Energy Cooperative released initial study results showing a 73% drop in bat fatalities when wind farm operations are stopped during low wind conditions, when bats are most active.
Bats avoid radar transmitters, and placing microwave transmitters on wind turbine towers may reduce the number of bat collisions.
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