Bats, despite their ability to use sonar to avoid moving objects, are susceptible to "’barotrauma", a sense of disorientation caused by the rapid change of air pressure created by a turbines rotating blade. An unexpectedly high number of bat fatalities have been recorded across the US and Europe over the past decade.
"A recent review of the problem put forward no less than 11 hypotheses as to what might be contributing to these [bat] fatalities," says the Centre of Sustainable Energy in Bristol in its publication Common Concerns About Wind Power. "Clearly, a great deal of research is still needed."
With regard to bird fatalities, it says: "Wind turbines represent an insignificant fraction of the total number of bird deaths caused by man-made objects or activities (eg building structures, transmission lines, and keeping domestic cats)." According to the CSE, for every bird killed by a wind turbine 5,820, on average, are killed striking buildings, typically glass windows.
However, UK planning laws now mean that bat and bird assessments must be conducted as part of the application process. "If wind farms are located away from major migration routes and important feeding, breeding and roosting areas of those bird species known or suspected to be at risk, it is likely that they will have minimal impacts," says the RSPB. "We are involved in scrutinising hundreds of wind farm applications every year to determine their likely wildlife impacts, and we ultimately object to about 6% of those we engage with, because they threaten bird populations. Where developers are willing to adapt plans to reduce impacts to acceptable levels we withdraw our objections, in other cases we robustly oppose them."
It stresses, though, that there are "gaps in knowledge and understanding" of how turbines impact on bird and bat populations: "The environmental impact of operational wind farms needs to be monitored – and policies and practices need to be adaptable."
Leo Hickman, www.guardian.co.uk/profile/leohickman