New research on bat migration patterns could impact the ongoing debate over the placement of energy-generating wind turbines.

Wind farm opponents cite a danger to migrating bats among reasons to stop turbine construction projects, including a controversial site in Somerset County. The Federal Aviation Administration recently determined that 15 of 30 windmills proposed at the project pose a hazard to aviation.

But a new study indicates that smarter, environmentally sensitive placement of windmills could sharply reduce bat mortality.

In a December 2009 article in "The Journal of Mammalogy," researchers from the University of Calgary in Alberta, Canada, concluded that not all bat species were at primary risk and not all windmills posed a threat. Erin F. Baerwald and Robert M.R. Barclay, of the school's department of biological sciences, wrote that migratory tree-roosting bats, not more common species, were most affected by wind farms, and that turbine height plays a key role in windmill-related bat mortality.

"Our results indicate that bats migrate in certain areas," wrote Baerwald and Barclay, "and that measuring migratory activity may allow wind energy facilities to be placed so as to minimize bat fatalities."

During the 2001-07 study, scientists examined bat carcasses or used acoustic monitoring devices at nine wind farms in southern Alberta to determine whether incidents of bat mortality were evenly distributed through the research area, and when the mortality occurred.

Compared to birds, long-distance migration is relatively rare among bats, and findings indicated that mortality was highest along nighttime routes of the migrating hoary, eastern red and silver-haired bats.

The heights of turbine towers played a key role.

"Fatality rates differed among the nine sites, partly due to differences in turbine height," they wrote. "... At sites with high bat activity, an increase in tower height ... increases the probability of fatality."

"The Journal of Mammalogy" is a publication of the American Society of Mammalogists.

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