LIVERMORE -- High above the Altamont Pass, eagles, hawks, ravens and other birds soar, hover and glide across the tawny landscape. From a hilly vantage point in the Vasco Caves parkland, one can see the patchwork of wind turbines dotting the ridgelines and saddles -- old and new, large and small, some operating and some not, with others in various stages of dismantling.
East Bay Regional Park District wildlife manager Doug Bell has spent many a day out on these dusty dirt roads over the past 10 years and says what he's seen is troubling. Once one of the world's most densely populated areas for golden eagles, the Altamont has become a "population sink" for the protected raptors. Eagles fly in, and too often, they don't fly out.
"It's one of the most painful things to come across, an injured or dying eagle," Bell says. "It's just such a meaningful symbol ... Short of preventing all deaths, which we can't do, (we need) to get it to a sustainable level so we can still have eagles in 100 or 200 years. What's going on now is unacceptable."
Although everyone agrees huge numbers of birds are dying on the Altamont Pass, they don't agree on how and why they are dying -- and what should be done about it.
Environmentalists say it's a no-brainer: The nearly 5,000 energy-generating turbines there kill birds, and the wind industry should be better regulated. But wind companies point to studies suggesting predators, poison and natural causes are to blame.
Scientists and biologists argue that this so-called "background mortality" is a misnomer, a concept pushed by the companies to shift responsibility and improve their public image.
In an effort to cut avian deaths in half by this year, the Altamont Pass Wind Resource Area -- a 37,000-acre zone stretching across eastern Alameda and Contra Costa counties that is home to 200 or so species of birds and bats -- is undergoing a massive transformation. After a 2007 settlement among Alameda County, three of the four major wind companies and environmental groups, the companies agreed that by October they would repower -- replace older-generation turbines with fewer, more efficient, more bird-friendly turbines. The remaining company, Altamont Winds Inc., did not sign the agreement and recently obtained an extension from the county to repower by 2018 -- a decision that drew intense criticism by environmentalists.
Still, no one is certain how well repowering will work and how many bird lives will be saved -- which means the debate over the role of the turbines is likely to continue.
According to counts conducted by Alameda County from 2005 to 2012, up to 4,600 birds die on Altamont wind farms every year, including about 900 burrowing owls, American kestrels and red-tailed hawks, as well as 40 or so golden eagles. But the counts indicate that 44 percent of the deaths over the past three years of the study occurred while turbines were not operating, leading some to hypothesize that other factors, including natural causes, predators and even rat poison, might be to blame.
Altamont's Scientific Review Committee, a five-member team that oversees studies conducted by consulting firm ICF International and makes recommendations to the county, responded to the findings by initiating yet another study -- funded by wind companies -- to look at what other factors besides turbines could be killing birds. That study is scheduled to be presented to the committee in July.
ICF's project manager, Doug Leslie, said the study makes a strong case that predators are to blame.
"We shut things off in the winter and we expect birds to stop getting killed, but that hasn't happened," Leslie said. The study "will provide evidence of what we already knew, that there are birds of prey out there that kill other birds, and those could be confused with the (turbine-related) bird deaths."
Ecologist and independent researcher Shawn Smallwood, who has conducted counts on the Altamont since 1999 and was a member of the Scientific Review Committee from 2006 to 2011, called the latest analysis "the most useless study that ever happened."
Smallwood estimates about 10,000 birds are killed every year, "about 99 percent" of them linked to turbines themselves or their infrastructure. Among those, about 60 are golden eagles, he said, making the Altamont the deadliest zone for the species in the United States.
Each of the five committee members declined to comment, some saying they would rather wait until after the committee is disbanded later this year.
Sandra Rivera, Alameda County assistant planning director, who oversees the committee, said the county's monitoring program is the most extensive and accurate study of bird deaths on the Altamont to date.
The park district's Bell, however, agreed with Smallwood that bird deaths are severely underestimated because of a lack of resources and a "crippling bias" that doesn't account for mortally wounded birds able to walk or fly away before dying.
Liz Leyvas, a biologist who has counted dead birds in the Altamont for both ICF and as an independent researcher, said a majority of deaths are caused by direct contact with turbines, whether they are operating or not.
"Birds can die or get sick, but usually if you see dead birds in a wind farm, it died in a turbine," Leyvas said. "You know because a wing or a limb is missing. The larger birds, like sea gulls, owls, vultures, hawks and eagles, those are dying because they are getting hit."
During shutdowns, Leyvas said, birds still die by running into the stationary structures during heavy fog or because they're scanning the ground for food. They are also often electrocuted or maimed by striking power lines linked to the wind farm's infrastructure.
Smallwood said a major reason for the county's low estimates is that the search intervals, which averaged 30 to 51 days, were too long to find many small bird carcasses that were quickly snatched up by scavengers. In addition, wind companies restricted where monitoring teams were allowed to go. Smallwood said he left the committee because he found the research "deeply flawed."
"The science could be better, but a lot of consultants have their hands tied by the wind companies," Smallwood said. "If they had the flexibility, they could do better counts. It's a problem, but what could help solve it would be regulatory agencies taking more control."
Smallwood and Leyvas recently wrapped up monitoring for a three-year study at NextEra Energy's repowered Vasco Winds project in East Contra Costa County. It's showing early indications that the newer turbines do in fact reduce deaths among raptors and other birds, Smallwood said. The final report is expected to be published in late fall.