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Biologist: Eagle Deaths at Wind Turbines Widespread, Undercounted

Bald eagle on a power pole | Photo: Mike Richardson and Sarah Winch/Flickr/Creative Commons License

Though California and Wyoming lead the nation in eagle deaths at wind turbine facilities, wind turbines are killing bald and golden eagles nationwide, and the death toll is mounting. That's according to Dr. Joel Pagel, a longtime raptor biologist now working with the U.S. Fish and Wildlife Service and the lead author of a recent peer-reviewed paper on wind facility eagle mortalities.

Pagel, who spoke with ReWire Friday about the paper he co-authored with five other USFWS biologists, said that additional confirmed mortalities have been coming in since the paper's completion. Mortalities have been reported since publication for bald eagles in Idaho and North Dakota and golden eagles in Montana and Nevada.

The stringent standards the authors used to determine whether to include individual mortality reports in the paper mean that the numbers are almost certainly an undercount, Pagel told ReWire.

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The paper, "Bald Eagle and Golden Eagle Mortalities At Wind Energy Facilities In The Contiguous United States," was published in September in the Journal of Raptor Research. In the paper, Pagel and his co-authors analyze 85 eagles killed at 32 wind facilities in 10 states between 1997 and June 2012, with nearly 80 percent of those fatalities taking place in the last five years.

Each one of the mortalities recorded is a violation of the federal Bald and Golden Eagle Protection Act, which could carry penalties of fines and jail time.

Pagel, a government raptor ecologist since 1983 who's also worked with the U.S. Forest Service, noted that the Journal or Raptor Research paper is far from being the final word on the extent of injuries eagles have suffered from wind turbine encounters.

"We relied on voluntary reports from turbine operators and other reports that were publicly available," Pagel said. "We excluded 17 possible mortalities because we just couldn't confirm them." In the absence of more systematic data collection, notes Pagel, he and his colleagues very likely compiled an incomplete tally of bald and golden eagle deaths due to wind turbine strikes. "I can't think of a factor that might contribute to our overcounting mortalities," Pagel told ReWire, "but there are plenty of reasons we have likely undercounted."

The undercount of bald eagle wind turbine mortalities in particular is perplexing, Pagel noted. "Bald eagles are ecologically very similar to white-tailed eagles in Europe, and there have been a lot of documented white-tailed eagle kills at wind turbines in places like Norway." One possibility noted in the Journal of Raptor Research paper: where bald eagle territories and wind developments overlap, tall farm crops can make recovery of carcasses unlikely. "If a bald eagle falls into a corn field, we might never find it," said Pagel.

According to the paper, California and Wyoming led the confirmed death toll with 27 and 31 confirmed mortalities, respectively. (The study omitted the notoriously high mortalities at California's Altamont Pass Wind Resource Area from consideration.) All of the Wyoming fatalities detailed in the study occurred since 2009, which is about when that state's fledgling wind infrastructure started taking off.

Wyoming's death toll is strikingly high compared to states with many more turbines, such as Texas (with one confirmed fatality) and Iowa (with three). Some of the discrepancy might well be due to sampling error: if Texas wind operators are letting eagle deaths go unrecorded, that one reported dead eagle might have plenty of company that's gone un-remarked upon.

But there's likely more than sampling error at work here. ReWire asked Pagel what might account for Wyoming's startling figures. "There are a lot of eagles in Wyoming," he replied. "Eagles visit Wyoming from as far away as British Columbia and Alaska. The Yellowstone Raptor Initiative has seen 100 migrating eagles in one day at Yellowstone National Park."

Pagel declined to identify to ReWire any of the wind facilities at which the documented eagle mortalities occurred, citing his restrictions as a federal employee from disclosing information which many wind companies claim is protected under the Uniform Trade Secrets Act. A cursory Google search, however, reveals that at least 10 of the Wyoming fatalities occurred at Duke Energy's Top Of The World wind farm after that facility began operations in 2010 near Casper. That would be about a third of all the state's documented mortalities.

Pagel noted that some of the injuries described were ghastly. "There was plenty of blunt force trauma in these reports," Pagel said. "Some of the birds were thrown long distances. Some of them had had portions of their bodies separated."

Given that eagles may move well away from the turbine base after having been injured by a turbine blade, it may be that under-counting such injuries and mortalities is inevitable. And eagles are far from the only birds injured by wind turbines, noted Pagel, who has worked extensively with peregrine falcons and other raptors. "We did not look at other raptors or other birds in this paper. We're just looking at two species here; bald eagles and golden eagles. We stuck solely to bald and golden eagles. That doesn't mean other birds aren't being injured. We just didn't examine those other species."

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About the Author

Chris Clarke is a natural history writer and environmental journalist currently at work on a book about the Joshua tree. He lives in Joshua Tree.
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