The three firms that operate the farm spanning nearly 55,000 wind-swept acres propose in a habitat conservation plan now pending along with a permit request before the U.S. Fish and Wildlife Service to increase the wind speed at which the farm's 355 wind turbines begin spinning and generating electricity.
Under that plan, the turbines would be programmed to begin spinning and generating power when the wind reaches 11 mph from sunset to sunrise between Aug. 1 and Oct. 15. That's the period when Indiana bats migrate through the area as they leave summer roosting sites en route to southern Indiana caves where they'll hibernate over the winter.
Below the 11 mph wind speed, the plan also calls for the three giant blades that drive each turbine to be oriented parallel to the airflow to make them spin slowly or not at all. Currently, the farms' turbine blades spin at low wind speeds — the nighttime conditions when bats are actively flying — and are oriented to take advantage of the slightest winds.
Georgia Parham, a Bloomington-based spokeswoman for the Fish and Wildlife Service, said the goal of the farm's proposed changes will make the turbines' blades more inactive at night and less dangerous to migrating bats during their fall migration. Bats of numerous species can be killed by collisions with the fast-moving blades or from lung injuries inflicted by rapid air pressure changes the spinning blades create.
Winds above 11 mph are generally too brisk for most bats and the insects they feed on to take to the skies, Parham said.
"At those higher wind speeds, it's less likely that bats would be flying," she said.
The wind farm's conservation plan states that based on surveys which found about 1,500 dead bats around some of the turbines, an estimated 10,000 bats of various species are killed each year passing through the wind farm. That includes an estimated 17 Indiana bats.
An estimated 850,000 to 1.7 million bats have died from collisions with wind turbines in the United States and Canada since 2000, said Mylea Bayless, director of conservation programs for Austin, Texas-based Bats Conservation international.
She said several other U.S. wind farms have drafted similar bat protection plans that have successful reduced bat deaths at those farms.
"We do know it works. All the data suggests that by doing this they're going to save bats — not just Indiana bats, but all bats," Bayless said.
She said bats play a key ecological role by devouring pest insects and a recent study found that they in reduced crop damage and pesticide use save U.S. farmers more than $3.7 billion a year.
But Indiana bats and many other bat species already facing pressure from wind farms are also facing the devastating effects of a fungus that's spreading across North America and has already killed millions of bats across the eastern U.S., Bayless said.
Fowler Ridge's proposed conservation plan states that the farm's proposed operational changes will cuts its annual Indiana bat deaths in half and reduce overall deaths of the species to no more than 193 during the farm's 22-year operational life.
BP Wind Energy oversees the farm, which it owns and operates with two other companies, Sempra Generation and Dominion Resources Inc. The three firms are seeking a Fish and Wildlife Service permit allowing the farm to "take" a certain number of Indiana bats each year through the operations of its electricity-generating turbines.
BP Wind Energy issued a statement Wednesday night saying its "conservation plan is a science-based solution to minimize the incidences of bat fatalities at the Fowler Ridge Wind Farm."
Under the farm's proposed permit, it would be allowed up to 11 Indiana bat deaths and as few as two annually over the farm's life. Those numbers vary because the farm will have various numbers of turbines operating over the next two decades. The farm currently has 355 wind turbines, but plans to add 94 others that will boost its total electrical generation to 750 megawatts.
Parham said the Fish and Wildlife Service is reviewing the farm's permit application and proposed conservation plan and expects to make a decision on those sometime this year.