鈥淏eware: exploding lungs鈥� is not a sign you would expect to see near a wind turbine, but it could explain why bats are dropping dead around the machines.
The risk that turbines pose to birds has long dogged the debate over wind energy. Now it seems bats face a greater risk, though why, as they can echolocate moving objects, has remained a mystery.
One theory was that high-frequency noise from the gears and blades disrupted their echolocation systems.Erin Baerwald of the University of Calgary, Canada, and colleagues examined 188 dead bats from wind farms across southern Alberta to see if this was true. They found that 90 per cent had signs of internal haemorrhaging, but only half showed signs of direct contact with the turbine blades (Current Biology, vol 18, p R695).
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Baerwald suggests that vortices which form around the tip of a moving blade create a region of low air pressure, and that when bats fly into this area their delicate lungs suddenly expand, bursting the blood vessels and killing the bat. As birds鈥� lungs are more rigid, and therefore more resistant to sudden changes in pressure, the team think they do not suffer the same fate.
Bats eat agricultural pests, so if wind turbines affect their numbers local ecosystems could be damaged. The effects might be global: 鈥淭he species being killed are migrants,鈥� says Baerwald. 鈥淚f bats are killed in Canada that could have consequences for ecosystems as far away as Mexico.鈥� One solution could be to raise the minimum wind speed needed to set the blades in motion since most bats are more active in relatively calm conditions.
