The interaction of bats and wind turbines is emerging as a major and unexpected problem in northern Appalachia. From mid-August through October 2003, during the fall migration period, at least 400 bats died at FPL Energy's 44-turbine Mountaineer Wind Energy Center on Backbone Mountain in West Virginia.

The bats apparently died by colliding with the wind turbines, but why so many animals were killed at this particular site remains a mystery. The public outcry over these numbers threatens to delay or halt construction of some of the additional several hundred wind turbines planned for the tristate region of West Virginia, western Maryland and south-central Pennsylvania.

Steve Stengel, a spokesperson for FPL, which is based in Juno Beach, Fla., says the company is cooperating with federal biologists to study the problem of bat kills at Mountaineer. "We don't know exactly why it happened," he states. "We're moving quickly to find out as much as we can." Some scientists believe that the migrating bats may not be using their echolocation when the collisions occur. Others speculate that the wind turbines may be emitting high-pitched sounds that draw the bats to the site. Still others suggest that the animals may be getting caught in wind shear associated with the turning turbines.

West Virginia biologists have identified the majority of the 400 bats that were recovered from the Mountaineer site--mostly common species such as red bats, eastern pipistrelles and hoary bats. "What's scary," remarks biologist Albert Manville of the U.S. Fish and Wildlife Service, "is that we may be finding only a small percentage of what's been killed." That is because bats are very small and difficult to find in the field; also, scavengers could discover the bat corpses before researchers do.

At issue is the length of time that wind-energy entrepreneurs are devoting to preconstruction wildlife studies. The Fish and Wildlife Service issued voluntary siting guidelines last summer, indicating that a census of wildlife activity should precede the building of a wind farm. Some biologists feel that such a census should last two years, although some energy companies believe this length of time to be excessive. (The guidelines are voluntary because in many cases the federal agency has little enforcement power unless an endangered or threatened animal is actually killed.)

Concerned that the endangered Indiana bat may be at risk at FPL's 20-turbine wind project in Meyersdale, Pa., wildlife advocates are threatening legal action. They allege that thorough habitat studies were not done in advance of construction at Meyersdale.

A letter last October from a bat biologist hired by the project's builders would appear to back them up. Pennsylvania State University's Michael R. Gannon spent two days last spring looking for bat caves on the future wind-farm site. He suggested that Indiana bats may use the site as a summer habitat and noted that at least a summerlong study might be appropriate. But industry biologists disagreed, Gannon says. "A two-year study should have been conducted prior to the installation of the turbines to determine the potential risk to bats," he wrote in his letter. "Unless and until these data are available, it should be assumed that this site is a flight path of the Indiana bats and that Indiana bats will be killed.... Data that are available indicate this as a very likely scenario."

FPL, which bought the project during development, still wants more information. "We are reviewing the matter," Stengel comments, "and after our review we will respond, if appropriate."

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Wendy Williams, based in Mashpee, Mass., writes for Windpower Monthly, an international news magazine.