On September 26, at 11 a.m., an environmental expert hired by Duke Energy to survey its North Allegheny Windpower Project in western Pennsylvania found the body of a small, brown bat more than 300 feet beneath the spinning blades of a wind turbine. Duke didn’t wait for a directive from the U.S. Fish and Wildlife Service. The company immediately suspended night operations of the wind farm and sent the carcass to the USFWS for evaluation.
Though wind turbines frequently kill bats—hundreds of thousands each year—this was an endangered Indiana bat, only the third ever found dead at a wind farm. Scientists estimate that there are 387,000 Indiana bats in existence, a roughly 50 percent decrease in the population since 1967, when the bat was listed as an endangered species. Duke had to balance suspending energy production that could power up to 21,000 homes against a potential lawsuit. In 2009, an environmental group filed suit over the mere presence of an Indiana bat in West Virginia, halting the construction of a proposed wind farm. “There certainly is an economic hit for suspending nighttime operations,” says Greg Efthimiou, a spokesman for Duke Energy Renewables. “But we felt that was the price of doing the right thing while we analyzed the potential cause and potential hazards to additional bats.”
The decision highlights a conflict between two federal environmental initiatives that are increasingly at odds with one another: the protection of endangered species and the development of alternative energy. In the past four years, wind-energy production has nearly quadrupled, according to the U.S. Energy Information Administration. During that time, there have been a number of high-profile animal fatalites, including large-scale bird die-offs, but bat fatalities may be an even greater concern. “Something really strange is going on, and it seems like it has the potential to seriously influence a population,” says Paul Cryan, a bat researcher for the USGS.
The scientific literature shows a few trends. The majority of bats killed by turbines are migratory tree dwellers—as opposed to cave-dwelling hibernators. Bats are killed most often on nights with low wind in the late summer or fall. And, at least some of the time, they’re not killed by the blades themselves, but by a drop in pressure near the quickly spinning rotor that causes blood vessels in the lungs to explode—a phenomenon called barotrauma. Barotrauma is like the bends for bats.
The 35 turbines at the North Allegheny Windpower Project tower more than 300 feet above the rolling woodlands of Cambria and Blair counties and spin 143-foot-long blades at up to 193 mph. But why are the bats close enough to a blade that a vortex rips their lungs apart in the first place? They could be there by random chance, flying higher and without echolocation as they pass through on migration. Or they could be attracted to the turbines. Maybe they mistake the noise of the blades for prey. Maybe they’re looking for the tallest place around to roost for the night. Maybe they collect there to mate.
The Indiana bat found on Duke Energy’s farm was a juvenile female, according to Clint Riley, supervisor for the Fish and Wildlife Service’s Pennsylvania field office. Scientists aren’t sure whether the death was the result of barotrauma or a strike. Its death has further confused scientists because it is a cave dweller and not the more commonly killed tree dweller, and it hasn’t really helped officials understand how to decrease the risk to bats. So though an ultrasonic sound blaster that could scare bats away from turbines is in development, the only practical option at this point, says Cryan, is curtailment.
Duke has resumed some night operations at the farm, but will turn them off on nights that bats are likely to be around. Winter, when bats are inactive, will offer a reprieve, but Duke is still negotiating with USFWS as to how it will proceed come spring. The negotiations could lead to an incidental take permit that would offer Duke some protection if another Indiana bat should be killed. Duke can continue to operate the plant at its discretion, but if the turbines kill another Indiana bat it would be a violation of the Endangered Species Act. The company could face a criminal or civil lawsuit, and possibly a fine or an injunction. Duke's decision to stop the blades minimizes risk, both to the company and to the bats. It's the company's most sensible option until the technology advances or humanity's understanding of bats improves.
“I’m pretty confident that if we can figure out what it is that makes them so susceptible, there'll be some solutions,” says Cryan.
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