SAN FRANCISCO — For decades, wind turbines straddling the Altamont Pass have generated clean electricity for California – at the cost of killing thousands of birds.
The tall, grassy hills, raked by stiff winds in spring and summer, offer prime hunting territory for owls, hawks and eagles. Focused on spotting prey, many birds soar straight into the spinning blades of turbines.
But efforts to curb the bloodshed may be starting to work.
A new study suggests that the number of eagles, kestrels, burrowing owls and red-tailed hawks killed at Altamont each year has fallen roughly 50 percent since 2005. Reaching that level has been a long-term goal of local environmentalists and government officials, as well as the energy companies running turbines in the pass.
“We’re pretty pleased with the results,” said Sandra Rivera, assistant planning director for Alameda County. “It’s a fine balance between having the renewables we all want to have in California and keeping the wildlife safe. That’s what we’ve all been trying to achieve.”
Bird lovers who sued both the county and the wind companies in 2006 say they’re encouraged by the numbers, although they don’t want to declare victory yet.
The steps taken to protect birds at Altamont – shutting down turbines for several months in the winter, replacing small, fast-spinning older models with larger ones that are easier for birds to avoid – appear to be working. But Michael Lynes, executive director of the Golden Gate Audubon Society, said he wants to keep pushing the numbers lower.
“We’re not celebrating, put it that way,” said Lynes, whose Audubon chapter was one of four filing the suit. “Because as long as wind turbines are operating out there, there’s going to be mortality to wildlife. We see this as a good step toward reducing mortality.”
The study comes from consulting firm ICF International and examines bird deaths from 2005 to 2010. It focuses in particular on four species that were at the heart of the lawsuit – American kestrels, burrowing owls, golden eagles and red-tailed hawks.
At the start of the study period, deaths of all those species combined averaged 1,245 per year. By the end, the total had fallen to 625. (Those numbers represent three-year, rolling averages, considered useful because the number of birds in the pass can vary from one year to another for reasons that have nothing to do with turbines.)
The numbers aren’t exact. Although researchers routinely search the wind farm for bird carcasses, they also take into account the possibility that scavengers will remove some of remains before they can be found. The report offers several different ways of calculating mortality rates, and while the results differ, all show a substantial decrease in deaths.
The decline is welcome news for wind power advocates, for whom Altamont’s bird-killing reputation had been an embarrassment. They considered the site an aberration, much more deadly than other wind farms.
“Those levels of collisions have never been replicated anywhere else,” said John Anderson, director of siting policy for the American Wind Energy Association. “That site was developed in the infancy of the industry, and between the landscape, the wind conditions, the avian activity – it really is a unique setting.”
The first turbines were installed in 1966, long before renewable power became a pressing concern as a means to fight climate change. The hills, which separate the Bay Area’s eastern edge from the Central Valley, now hold roughly 4,500 turbines, scattered across 37,000 acres.
At least 13 turbine models have been installed there over the years, and some proved particularly lethal to birds, as well as bats. Many older models had relatively small blades that spun fast in the wind.
New turbines, in contrast, are far larger, with long blades that don’t whirl at the same frantic speed. They also generate much more electricity than older models, so one new turbine can replace several old ones, a swapping-out process that the wind industry calls “repowering.”
The Audubon chapters that filed suit in 2006 agreed to a settlement that gave the wind companies until November 2009 to cut bird deaths by 50 percent.
The companies tried shutting down turbines during the winter months, when migrating birds cross the area and winds are relatively light. But the 50 percent goal remained elusive.
A second settlement, in 2010, committed the largest company operating in the pass to replace or remove thousands of old turbines. NextEra Energy Resources has so far removed 800 of the machines, replacing them with 34 newer models.
‘Much better approach’
In addition, the company puts more thought into where it places turbines, Lynes said. Researchers study how birds use the different hills, saddles and ridges and look for locations that will reduce problems.
“We think that’s a much better approach than what we had in the past,” Lynes said. “When they put these in in the ’80s, they didn’t do anything like that. They just threw up hundreds of turbines at a time.”
But no location is risk free. And while bird deaths appear to be dropping, they won’t end altogether. The local population of golden eagles already has shrunk so much that it may not survive long term, said Doug Bell, wildlife program manager for the East Bay Regional Park District.
“The best approach to reducing mortalities would be to repower the whole thing,” said Bell, who is working on a separate bird mortality study at Altamont.
“It still wouldn’t get us out of the woods. You put an object up into an air column – a tower, turbines, wires – and things that fly are going to get killed whacking into it.”
David R. Baker is a San Francisco Chronicle staff writer. E-mail: email@example.com Twitter: @davidbakersf