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Assessments understate ecological risks of wind turbines, British study finds

Wind farms pose a potentially lethal threat to bat populations, and environmental impact assessors do a poor job of predicting – let alone overcoming – the risks.

British researchers have found that scores of bats are killed each month at some of the country’s wind farms, possibly after being attracted by the spinning blades. Deaths occur both at sites found to pose little danger and at places the risks have supposedly been addressed.

The team blames the casualties, reported this morning in the journal Current Biology, on a combination of factors. Pre-construction research into the impacts is ineffectual, the findings are deliberately downplayed, and bats change their behaviour after wind farms are built.

Co-author Fiona Mathews said the findings threw doubt on the entire environmental risk management process, and suggested the only way to protect bats was to slow down or stop wind turbines at night.

“There has been an assumption that it is possible to ‘design out’ potential impacts on bats by siting the wind farm in the right area, for example,” said Dr Mathews, an environmental biologist with the University of Exeter. “I don’t think this assumption is safe. We need instead to focus on implementing the strategy that we know is effective: minimising the spinning of blades at times of high risk to bats.”

The team surveyed bat deaths for a month at 49 British wind farms, relying on search dogs to find the tiny corpses. Casualties were recorded at half the sites, with the most – 64 – at a farm where the turbines had been repositioned to protect bats.

While ecological impact assessments were available for 29 of the farms, they did not accurately predict the risks to bats. “Even in those cases where high risk was correctly identified, the mitigation deployed did not avert the risk,” the paper says.

Studies into wind farms elsewhere have found bat fatalities in Australia, Africa, Europe and the Americas. Bats perform important ecological roles in dispersing seeds, pollinating plants and controlling insects.

Dr Mathews said the deaths her team had recorded would have very little impact on some local populations, but could be “very damaging” to others. “The tricky part, as shown in our study, is trying to predict in advance which scenario will apply,” she told The Australian.

Scientists believe bats could be attracted by ultrasound emitted by wind turbines, or by insects trapped in the whirling air around the blades.