At a time when demand is rising for greener energy sources, the Altamont Pass is a leading producers of wind power in the US, generating enough electricity annually to power 120,000 homes.
Over 5,000 windmills line the hilltops, so migrating birds get chopped up in fast-rotating turbine blades as they fly through or hunt for prey.
1,700 to 4,700 birds are killed each year in the Altamont Pass Wind Resource Area. Between 880 and 1,300 are federally protected raptors such as burrowing owls, red-tailed hawks and golden eagles, according to the California Energy Commission.
Environmentalists were once reluctant to take on an industry that provides an eco-friendly alternative to fossil fuels.
Bird deaths have prompted wildlife advocates to sue wind farm operators and appeal Alameda County's decisions to renew their operating permits without requiring measures to reduce bird collisions.
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