Scores of protected golden eagles have been dying each year after colliding with the blades of about 5,000 wind turbines along the ridgelines of the Bay Area’s Altamont Pass Wind Resource Area, raising troubling questions about the state’s push for alternative power sources.
The death count, averaging 67 a year for three decades, worries field biologists because the turbines, which have been providing thousands of homes with emissions-free electricity since the 1980s, lie within a region of rolling grasslands and riparian canyons containing one of the highest densities of nesting golden eagles in the United States.
“It would take 167 pairs of local nesting golden eagles to produce enough young to compensate for their mortality rate related to wind energy production,” said field biologist Doug Bell, manager of East Bay Regional Park District’s wildlife program. “We only have 60 pairs.”
The fate of the Bay Area’s golden eagles highlights the complex issues facing wildlife authorities, wind turbine companies and regulatory agencies as they promote renewable energy development in the Altamont Pass and across the nation and adds urgency to efforts to make the technology safer for wildlife, including bats, thousands of which are killed each year by wind turbines.
Gov. Jerry Brown in April signed into law a mandate that a third of the electricity used in California come from renewable sources, including wind and solar, by 2020. The new law is the most aggressive of any state.
The development and delivery of renewable energy is also one of the highest priorities of the Interior Department, which recently proposed voluntary guidelines for the sighting and operation of wind farms. Environmental organizations led by the American Bird Conservancy had called for mandatory standards.
The U.S. Fish and Wildlife Service authorizes limited incidental mortality and disturbance of eagles at wind facilities, provided the operators take measures to mitigate the losses by replacing older turbines with newer models that are meant to be less hazardous to birds, removing turbines located in the paths of hunting raptors and turning off certain turbines during periods of heavy bird migration. So far, no wind energy company has been prosecuted by federal wildlife authorities in connection with the death of birds protected by the Migratory Bird Act, the Bald and Golden Eagle Protection Act or the federal Endangered Species Act.
The survival of the Bay Area’s golden eagles may depend on data gathered by trapping and banding and then monitoring their behavior in the wilds and in wind farms.
On a recent weekday, Bell shinnied up the gnarled branches of an old oak to a bathtub-sized golden eagle nest overlooking a canyon about 25 miles south of Altamont Pass.
Two fluffy white and black chicks, blinked and hissed nervously as he scooped them up and placed them into cloth sacks. He attached the sacks to a rope and delicately lowered them 45 feet to the ground.
“As adults, these birds could eventually wind up anywhere in the Western United States or Mexico – that is, if they live that long,” Bell said.
With field biologist Joe DiDonato, he banded the birds’ legs and recorded their vital statistics in a journal that chronicles more than a decade of raptor research in the region. The message is a grim one.
Each year, about 2,000 raptors are killed in the Altamont Pass by wind turbines, according to on-site surveys conducted by field biologists. The toll, however, could be higher because bird carcasses are quickly removed by scavengers.
Environmentalists have persuaded the energy industry and federal authorities – often through litigation – to modify the size, shape and placement of wind turbines. Last year, five local Audubon chapters, the California attorney general’s office and Californians for Renewable Energy reached an agreement with NextEra Energy Resources to expedite the replacement of its old wind turbines in the Altamont Pass with new, taller models less likely to harm birds such as golden eagles and burrowing owls that tend to fly low.
The neighboring Buena Vista Wind Energy Project recently replaced 179 aging wind turbines with 38 newer and more powerful 1-megawatt turbines. That repowering effort has reduced fatality rates by 79% for all raptor species and 50% for golden eagles, according to a study by Shawn Smallwood, an expert on raptor ecology in wind farms.
It remains unclear, however, whether such mega-turbines would produce similar results elsewhere, or reduce fatalities among bats.
Nationwide, about 440,000 birds are killed at wind farms each year, according to the Fish and Wildlife Service. The American Wind Energy Assn., an industry lobbying group, points out that far more birds are killed each year by collisions with radio towers, tall buildings, airplanes, vehicles and in encounters with hungry household cats.
And while “there’s quite a bit of growth to come in wind energy development, it won’t be popping up everywhere,” said attorney Allan Marks, who specializes in the development of renewable energy projects. “That is because you can only build these machines where the wind is blowing. So a lot of the new development will be replacing old facilities in areas such as Cabazon, the Tehachapi Mountains and Altamont Pass.”
Nonetheless, the generating facilities will continue to threaten federally protected species such as eagles and California condors, a successfully recovered species that is expanding its range into existing and proposed wind farms in Kern and Fresno counties.
NextEra Energy’s proposed North Sky River Project calls for 102 wind turbines across 12,582 acres on the east flank of the Piute Mountains, about 17 miles northeast of the Tehachapis. A risk assessment of that project warned that condors spend considerable time soaring within the potential rotor-swept heights of modern wind turbines, which are more than 200 feet tall. It also pointed out that condor roosts are as close as 25 miles away.
“We taxpayers have spent millions of dollars saving the California condor from extinction,” said Gary George, spokesman for Audubon California. “How’s the public going to feel about wind energy if a condor hits the turbines?”
In the meantime, raptors such as golden eagles, American kestrels, red-tail hawks and prairie falcons continue to compete with wind turbines for their share of the winds blowing from the southwest through the Altamont Pass.
Golden eagles weigh about 14 pounds, stand up to 40 inches tall and are equipped with large hooked bills and ice-pick talons. Their flight behavior and size make it difficult for them to maneuver through forests of wind turbine towers, especially when distracted by the sight of prey animals such as ground squirrels and rabbits.
“The eagles usually die of blunt-force trauma injuries,” Bell said. “Once, I discovered a wounded golden eagle hobbling through tall grass, about a quarter mile from the turbine blades that had clipped its flight feathers.”
As he spoke, an adult male golden eagle glided a few yards above the contours of Buena Vista’s sloped grasslands, prowling for prey. It floated up and over a rise, narrowly evading turbine blades as it followed the tantalizing sight of a ground squirrel scurrying through the brush.
Bell sighed with relief. “A wind farm owner once told me that if there were no witnesses, it would be impossible to prove a bird had been killed by a wind turbine blade,” he said. “My response was this: If you see a golden eagle sliced in half in a wind farm, what other explanation is there?”
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