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LIVERMORE, Calif. – They’re touted as the future of energy production – clean, efficient and renewable. But there’s a dark side to wind turbines for local wildlife – towers and spinning blades kill thousands of birds and bats on the Altamont Pass east of Livermore each year.

While the hazards there aren’t unique, recent studies suggest up to twice as many birds are killed every year at the Altamont Wind Resource Area than previously indicated by official estimates. Independent researcher Shawn Smallwood, head of ongoing mortality surveys in the Sand Hill area and other parts of the Altamont, estimates 10,000 birds are killed each year. It’s particularly dangerous for golden eagles; about 60 die annually, he said, making it among the most lethal zones for the species in the country, based on available records.

“The old (turbine) technology is terrible,” Smallwood said. “It kills a lot of birds and bats. It’s like a person running across a very busy street. You make it some of the time, but once in a while, you don’t.”

Nationwide, investors put $25 billion into wind energy in 2012, with U.S. wind farms reaching 60 gigawatts of capacity, according to the American Wind Energy Association. California is second only to Texas in total wind capacity, with $11 billion in capital investment.

Altamont Pass – one of the largest concentrations of wind farms in the country – is in the middle of decommissioning 4,000 old turbines that use 1970s and ’80s technology; nearly all will have to be removed or replaced by 2018. The world’s most heavily studied area for wildlife impacts could also be the proving ground for a new type of turbine that county officials and ecologists hope will be less deadly.

Since 2012, Smallwood and his team have been studying flight behavior and counting dead birds every four days for wind energy company Ogin Inc. The company is seeking Alameda County’s approval to install 40 of its “shrouded” turbines in the Sand Hill area to test its theory that the turbine’s unique design will help prevent golden eagles, red-tailed hawks and other species from colliding with the blades, hopefully reducing deaths.

The key is the shroud – two concentric covers around the blades – which the company says not only make them more efficient than older turbines, but also less accessible to approaching birds and bats. At less than 200 feet, they’re shorter and smaller than most “next-gen” turbines, which can reach almost 500 feet.

“It’s a visual and physical obstacle that, in theory, will prevent birds from flying into the rotor zone,” explained John Howe, Ogin’s vice president of public and environmental affairs.

The three-year avian impact study could influence how conventional turbines are phased out from the Altamont and elsewhere.