It's easy to see why wind turbines are at least potentially hazardous for birds: Massive blades with tips spinning at up to 179 mph (80 meters per second), hundreds of feet (at least 30 meters) in the air, are an obvious problem for anything flying near them [source: MIT]. The fact is, birds do fly into the path of the blades and die a grisly death. Most of the affected birds are songbirds, and about 10 percent are birds of prey like raptors [source: ABC]. It's the raptors that started all the protests, when hundreds of carcasses were found strewn across Northern California's Altamont Pass wind farm.

Bird conservationists took great interest, and the misconception that wind turbines pose a major threat to bird populations grew from there. By applying the mortality rates at Altamont Pass to every wind farm in the United States, the bird-mortality figures became extremely inflated. In fact, Altamont Pass is a unique case of a wind farm that is truly a significant hazard to birds.

Altamont Pass is different for two main reasons: turbine location and turbine design.

There are more than 4,000 wind turbines at the Altamont Pass energy farm in California. It's one of the first wind farms in the United States, and its 20-year-old turbines are accordingly out-of-date. Their design has long since been abandoned: Latticework blades with small surface area are far from efficient for energy generation, and far from safe for birds. The lattice structure actually attracts large birds, because the frame makes for an excellent perch. Large birds like raptors are drawn to the blades, and collision rates are high as a result.

The other design issue is the blades' low surface area, because less surface area means the blades have to spin faster to turn the electricity-generating turbines. The faster the blades spin, the more dangerous they are to birds flying near them. It's unlikely that a bird that finds itself in the vicinity of the blades could ever make it through when they're spinning so fast.

As if this weren't enough to make old wind farms a bird nightmare, the Altamont Pass power plant was built smack dab in the middle of a major migratory route for large birds. The area also houses the world's largest single population of golden eagles [source: USA Today].

The total for all wind farms in the United States, is 140,000 to 328,000 per year according to a 2013 estimate [source: Loss, et al.]. ­Even though up to 1 billion birds die each year by flying into windows, no one is brushing off the tens of thousands of turbine-related deaths every year. So what are we doing to lower that number? On the next page, we'll see what changes are being implemented to save the birds.

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