LANDER -- Wind farms and golden eagles seem have trouble coexisting.
But conservationists, biologists and energy companies agree: No one really knows what harm wind farms cause to golden eagles and their numbers.
The available data, science and policy haven't caught up with the pace of wind energy development. Still, wind energy development is apparently killing golden eagles, which seem especially susceptible to collisions with the turbines.
"We really don't know how many birds are being killed by wind turbines," said Trish Sweanor, a U.S. Fish and Wildlife Service biologist.
Turbines kill, displace eagles
Golden eagles are found throughout the country, from deserts to grasslands, according to the Fish and Wildlife Service. They eat mid-sized reptiles, birds and mammals as large as mule deer fawns and coyote pups.
They also are protected by three federal laws: the Bald and Golden Eagle Protection Act, the Migratory Bird Treaty Act and the Lacey Act. These laws prohibit possession or sale of eagle feathers and parts and have protected bald eagles since 1940 and golden eagles since 1962 by making it a crime to kill the birds.
Wind turbines harm birds in three ways: direct collision, displacement or creating a space that birds avoid, and habitat fragmentation, which means large areas needed by some birds for nesting are dissected. The biggest issue is collision, Sweanor said.
Blades move at 180 mph and create motion smear, or the appearance they've disappeared. No one has discovered a way yet to alert birds to the danger of a turbine and steer them elsewhere, Sweanor said.
Feds expect bird deaths
There are 20,722 golden eagles in the West -- 80 percent of the species range in the lower 48 states -- out of approximately 30,000 in the United States, according to a Fish and Wildlife fact sheet about the species.
However, golden eagles undergo a 10-year population cycle and there is data only from four years.
Also not understood is exactly how many golden eagles are in Wyoming, Sweanor said. It's difficult, especially with migratory birds, to get accurate counts using collars without disturbing the birds or without conduting more specific golden eagle studies, she said.
To create estimates on fatalities, the Bureau of Land Management uses an average for wind turbines of all sizes, Murdock said.
According to the BLM's draft environmental impact statement for the Power Co. of Wyoming's project, there isn't bird fatality data for three-megawatt turbines, those proposed for the project.
There is still a lot of debate about whether or how the different-sized turbines impact numbers, she said.
But for now, the agency uses a rate that expects four raptors will die per year for every 100 megawatts of wind power generation. That means the Chokecherry and Sierra Madre wind project could kill 120 raptors a year, including 36 golden eagles.
Eagle kill rates elusive
That's a far lower number than an estimate produced by HawkWatch International, a Salt Lake City-based nonprofit group dedicated to monitoring and protecting birds of prey. The group predicted more than 700 raptor deaths at the project per year, including more than 200 golden eagles.
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But Power Co. of Wyoming expects a lower kill rate than the BLM ratio because of the company's extra mitigation steps, such as using avian radar, Choquette said.
Clearly, it's hard to nail down a number.
"Essentially what it means is, we aren't very good at estimating fatalities," said Sophie Osborn, a wildlife biologist and the Wyoming Outdoor Council's wildlife program director.
HawkWatch International Conservation Director Steve Slater agreed.
"We don't really know enough to come up with a precise impact number," he said. "You get 15 different consulting firms using 15 different methods."
Then conservation groups and agencies use their own types of modeling. The federal Fish and Wildlife Service's guidelines, when finalized, will hopefully help solve the confusion, he said. But long-term studies on eagle populations, including data from before and after a wind farm is developed, will still be needed.
Losing 200 golden eagles at a wind farm would not be sustainable to the population, Osborn said. Even 36 a year is a high number for the birds, which reproduce slowly with only about one or two young a year.
"People lose enthusiasm for wind energy when they are killing a lot of birds," she said.
That doesn't mean wind energy is bad, it just depends on where it is developed and the siting process, Osborn said. It also would help if there were more numbers to evaluate.
Getting the numbers
Some wind farm developers do sampling to find out the number of birds killed, but it can be erratic and not all farms are required to seek out dead birds, Sweanor said
Wind farms that go through the industrial siting process perform two years of bird fatality sampling. After that, there isn't a requirement to search for bird bodies, she said.
How often a company monitors for bird fatalities depends on the siting process, said Mark Tallman, vice president of renewable resources for Rocky Mountain Power, which owns nine wind projects in Wyoming, all on private land.
Some projects might monitor once a month, looking for dead birds; others might monitor every three months. It depends on the area and the mitigation tactics used, he said.
Monitoring does not involve searching around each turbine, but is performed using a statistically valid number of searches, Tallman said.
So far this year, for Rocky Mountain's 13 projects, there have been six eagle deaths, most of them golden eagles, Talmann said.
Because of the eagle deaths at its wind farms, Rocky Mountain Power has started performing more monitoring and additional searches, specifically for eagles, he said.
"Any time you have an eagle, the sirens go off and you deal with that in a focused way," he said.