Large numbers of bats are killed by colliding with turbine blades or by experiencing sudden depressurisation immediately adjacent to the blade.
In an attempt to reduce this mortality rate, Aberdeen University scientists Barry Nicholls and Paul Racey, funded by the People's Trust for Endangered Species (PTES), have shown that there is a significant reduction in bat activity when a portable radar beam is directed at their foraging sites.
There are now 206 operational wind farms across the UK, with 2,381 turbines in use. Plans for another 444 sites means that the effects on the UK's bat population – not to mention birds – could be significant.
Although little work has been carried out in the UK, a six-week study on two American farms in 2004 recorded a total of more than 4,500 bat fatalities from collisions with the turbines.
Attempts at mitigating bird collisions with wind turbines have typically involved the use of visual stimuli to make the turbine blades more conspicuous.
However, this clearly would not work well for bats, where hearing is their primary sense. Anecdotal evidence, including that of bats foraging offshore in Sweden avoiding an area around Utgrunden lighthouse, where a powerful radar was in permanent operation, led Nicholls and Racey to investigate whether a deterrent effect can be replicated by using a small portable radar system.
Over the summers of 2007 and 2008 they carried out repeated experiments using both rotating and fixed radar antenna, and different pulse lengths to see which – if any – methods were the most effective.
Encouragingly, their results demonstrated that an electromagnetic signal from a small radar unit with a fixed antenna significantly reduced the foraging activity of bats within 30m of the unit. The effect is reversible – bats return when the radar is switched off and not all bats leave when it is switched on.
Commenting on these initial findings, Nida Al-Fulaij, development officer at the PTES, said: 'We are delighted that this important research is leading to practical conservation outcomes that will effectively protect bat populations.'
Future work now needs to be conducted by radar engineers, working in conjunction with bat biologists, to develop a portable radar system that can be manipulated to produce a wider range of electromagnetic outputs. The parameters most likely to be important are the frequency, pulse length/pulse repetition rate and power output of the signal.