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Alarming evidence of bat kills in eastern US -- Scientists call on wind industry to help solve mystery of serious level of bat mortality at wind turbine sites

Bat kills are emerging as a major and unexpected problem at wind turbine sites in the United States. The issue was brought to a head last month after the death of what scientists describe as an "alarming" and "surprising" number of bats in a single wind farm over what appears to be the course of about four weeks, starting August 19. At least 250 bats died in that period at the Mountaineer Wind Farm on Backbone Mountain in West Virginia. If the kills are related to seasonal bat migration in the Appalachian mountains, which runs from August to November, scientists fear continuing deaths in coming weeks. The wind farm started operation in late 2002.

The owner of the 64 MW wind farm of 44 NEG Micon 1.5 MW turbines is FPL Energy, which is working with experts to identify why the bat kills are happening at the site and which species of bat are involved. "At this point we really don't know the cause of the bat incident," says the company's Steven Stengel. "We do know it was a low wind month, so many of the turbines were not even spinning." The carcasses were spread evenly through the site and not mangled, he adds. "We are obviously doing everything we can to understand it and hopefully mitigate that in the future." Company researchers believe the problem of the kills at Mountaineer will not continue, says Stengel.

FPL has hired a company called Pandion Systems to investigate the incident and has sent the bat carcasses to the West Virginia Department of Natural Resources for identification. Of 132 bats so far examined, no threatened or endangered species have been identified, stresses Stengel. According to David Densmore, supervisor for the US Fish and Wildlife Service (USFWS) in the Pennsylvania and West Virginia region, there are several endangered bat species in the West Virginia mountains. If one is killed, the USFWS can intervene with the force of law.

The incident in West Virginia ranks among the worst ever recordings of bat kills at an American wind turbine site, according to scientists who have been studying the phenomena for several years. Bats have been killed at wind plant sites throughout the US, but particularly east of the Mississippi River. This could be because the eastern part of the US is more forested, says Chuck Nicholson, who has been overseeing a three year study of bat mortality at a three turbine wind plant on Buffalo Mountain in Tennessee. Nicholson, a National Environment Policy Act (NEPA) specialist with the Tennessee Valley Authority, says his study has revealed bat mortality "an order of magnitude higher" than bat kills found in the Midwest and West. The NEPA is legislation dealing with endangered species.

FPL is now gathering all available data on bats and wind power sites, including research into bat kills at long established wind farms on Buffalo Ridge in Minnesota and Foote Creek Rim in Wyoming, says Stengel. But very little is known about the problem. Currently, some estimates of bats killed at certain sites range from about two bats per turbine per year to 20 bats per turbine per year. The data, however, is extremely rough, caution scientists. Very little is known about most of the 1000 or so bat species that exist -- and almost nothing about their migratory habits and requirements.

Bigger risk

"Right now, the picture that's emerging is that bats populations are more at risk from wind turbines than birds. It looks like this might apply mostly to bats that are migrating, but we don't know for sure," says Maarten Vonhof, a bat biologist at the University of Tennessee, where a study on the problem is in process.

"They talk about lighting the towers to prevent bird impacts, but the lights they're using may be more likely to attract bats. My perspective is that these are migratory bats that are hitting these turbines. The problem is that nobody knows where bats migrate from or where they migrate to," says Vonhof. "We don't have the basics to assess whether these are major migratory flyways or what's going on." He adds that it would not be technically difficult to find the answers, using "isotope signatures" and DNA molecule markers to track bats. But it would take significant investment.

large numbers

Vonhof says the numbers involved in the West Virginia incident are alarming. "Well, 250 bats in a single site, if you do that repeatedly, you're going to have trouble. Bats are very long-lived animals. The record for a hibernating bat is 35 years," he explains. "Bats have one of two pups a year, so if you begin to kill large numbers, you could pretty quickly impact population sizes."

James Simmons, a bat researcher at Providence's Brown University, agrees: "This is a surprisingly large number of deaths. You wouldn't expect to have 300 bats going through that small volume of space unless something is going on. You want to know what it is that's bringing the bats through that very small area. Are these machines set up so they just happen to be in the way of a migratory route or near a bat roost. Or is there something else about the turbines, perhaps the blades, that are attracting the bats?"

Another highly respected bat researcher, Donald Griffin, says that aside from the important role bats play in insect reduction, particularly mosquitoes, there are people who care about bats who will complain. "This would appear to be at least a public relations problem," he says. Griffin is an emeritus scientist who discovered before World War II that bats "echolocate," meaning that they use an inborn system similar to radar to hunt for their prey and to navigate.

The wind industry could help solve the puzzle of the bat kills in West Virginia by the timely release of relevant data, including numbers involved, genus and species involved, circumstances under which the animals are killed, time of night when the deaths occurred, age of the dead animals, and other relevant information. Money for this research is needed.

Densmore of the USFWS is concerned that while the agency has no authority to intervene unless an endangered or threatened species is involved, it has not been given any comprehensive data on the Backbone Mountain kill by FPL. "We don't have anything but the bodies. Whether they're flying into structures or flying into blades, we have no way of knowing. We have no way of knowing whether this is the end to it, or whether this is just the tip of the iceberg. Is this an occurrence peculiar to just this wind farm?"

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