Changing blade shapes and emitting ultrasonic sounds could save hundreds of bats.
courtesy Robert Barclay

Quest for clean energy kills bats

Sudden pressure change causes creatures' lungs to pop

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University of Calgary researchers solved the mysterious deaths of migratory bats near Pincher Creek.

Over the last two years, researchers studied hundreds of bat carcasses found under wind turbines and dissected them to determine the cause of death. Supervised by U of C biology professor Robert Barclay, the researchers determined the majority of bats killed suffered from barotrauma­-- physical damage caused by a difference in pressure inside and outside the body. Barotraumas affect respiratory systems when air pressure suddenly drops, causing the lungs to over-expand. Only 10 per cent of bat deaths come from collisions with wind turbines.

Bats have mammal lungs, similar to those of humans, that are pliable and balloon-like, unlike bird lungs which are more rigid and tube-like. Project leader Erin Baerwald pointed out the bats' lungs make them more vulnerable to sudden air pressure changes because the sacs can over-expand, bursting the capillaries around them and causing injuries and death.

"The pressure is sudden and therefore not detectable," said Baerwald. "Bats just can't avoid something they can't detect, leading to these deaths."

Researchers have no idea why bats are attracted to turbines, but theorize the bats are looking for food.

"Maybe the bats see the tall turbines as trees to roost in," said Baerwald. "We're not sure, maybe it's a combination of these theories. Perhaps they're attracted to the motion or sounds of the turbines."

Barclay is concerned about the number of bats being killed by wind turbines. He worries that the changes to the ecosystem could mean more insects, normally reduced by migratory bats that eat them on their way to warmer areas. There are nine species of bats found in Alberta, including hoary bats, eastern red bats and silver-haired bats, which migrate every year.

"We still don't know how many of these species of bats there are and if the numbers is significant ecologically," admitted Barclay.

He explained that bat deaths are hard to count because of their solitary nocturnal habits. Why they are near the wind turbines and how to reduce the number of deaths have yet to be discovered.

"If we can understand where the bats fly, we may be able to place wind farms away from these migration routes," said Barclay.

He mentioned that other scientists are testing high frequency sounds as a possible warning to keep bats away. However, Baerwald was skeptical of the usage of sound to scare off bats.

"It takes a lot of energy to make a loud enough ultrasonic sound to clear bats," he said. "Also, most positive tests have been done on foraging bats, not migrating bats. We think migrating bats may not rely on sound as heavily as foraging bats due to difference in nature. Migratory bats have to fly frequently and eat on the way, so they hear in different ways."

Baerwald suggested shutting off turbines in low wind speeds at night when bats are active during fall migration. When this was tested, fatalities were reduced.

Barlay is not against wind turbine farms and believes renewable energy is environmentally important, but acknowledged the wind farm's impact on the environment.

TransAlta Utilities approached Barclay and Baerwald after several wind farmers noticed bat carcasses below turbines. It contributed funding to the project and helped by turning off the turbines during periods of migration to see if it reduced the mortality rate. In an interview with CBC on Sept. 8, TransAlta said it was considering sound emitters or changing the blade characteristics so bats' sonar work better.