Bats may never find wind farms as friendly as belfries, but a three-month study in northeast British Columbia is designed to make the power-generating turbines at least somewhat less deadly.

Monitoring devices installed by AltaGas at the site of the proposed Bear Mountain Wind Farm have been recording data on the population and migratory routes of bats in the area since July.

In later stages of development, the research is intended to help how the company can make its turbines to more bat-friendly.

"During the environmental assessment, bats were identified as something we need to be mindful of," said Jim Bracken, AltaGas senior vice president of major projects. "Now we need more information to see if the wind farm will create any significant impact on the local bat population."

Bats have become unintended casualties in the rush to harness wind power. Researchers say it's not uncommon to find hundreds of dead bats at the base of North American wind turbines. About 600 dead bats a year are found at the Summerview wind farm in Pincher Creek, Alberta.

Erin Baerwald of the University of Calgary, Alberta, lead author of a recent report on bat deaths in the journal Current Biology, said there is often no immediately visible cause of death.

"Many of the bat carcasses found had no external injuries, lacerations or broken wings . . . something to indicate they had been hit by large, quickly moving objects," she said.

Baerwald, whose team has checked for bats underneath turbines daily since 2006, said a new generation of tall turbines cause changes in air pressure, causing bat lungs to burst. Traditionally, wind farm design has been more focused on reducing bird kills

She said 90 percent of the carcasses that were examined showed signs of internal hemorrhaging consistent with sudden drops or changes in air pressure.

"The numbers of bodies and circumstances of death caught the wind and energy industry off guard," she said. "They never thought bat kills would become an issue."

Bats are more susceptible to drops in pressure because bird lungs are rigid, tube-like and thus more able to withstand fluctuating air levels, while bats have a two-way air flow ending in thin flexible sacs and capillaries that can easily be made to expand excessively and burst.

Baerwald said there's little indication why bats are drawn to blades that can reach speeds of more than 150 mph.

"Many of the species are roosting bats, so perhaps they are attracted to turbines because they see them as roosting trees, or maybe they are attracted to insects that are near the turbine," she said. "It's all hypothesis at this point."

Scientists say reducing the bat death toll is important to ecological balance.

"They are really unique flying mammals that can eat up to 600 mosquitoes-sized bugs, including crop pests, an hour - and that's a small bat," Baerwald said.

TransAlta Wind, which initiated the University of Calgary study, has been working with Baerwald and a team of bat specialists on ways to reduce the toll.

"Interestingly enough. the schemes we are looking at are working," said Jason Edworthy, director of stakeholder relations for TransAlta Wind. "We noticed a 50 percent reduction in collisions."

Research indicated bats can't get close to turbines in high winds, averting crashes and internal trauma, so TransAlta Wind boosted the speed on 19 of 38 turbines at Summerview a year ago and found that bats were being driven away.

"This year we've upped the experiment by increasing the speed on more turbines," Edworthy said.