Harvest the Wind by Philip Warburg

Author:Philip Warburg
Language: eng
Format: epub
Publisher: Beacon Press

From the early days of wind energy development, it was obvious that birds were being killed by turbines. The toll on bats was initially less apparent. Even today, experts are careful to point out that most of the data on bat mortality at wind farms has come from surveys that were primarily focused on birds.39

Available studies may still be limited, but they reveal a level of bat mortality that is of real and mounting concern. Studies conducted at wind farms in the West and Midwest point to annual bat kill rates ranging from 0.8 to 8.6 per megawatt—more or less in line with reported death rates for birds. Along some forested ridgelines in the East, however, the losses have been much higher, reaching as high as 41 bats per megawatt at the Tennessee Valley Authority’s Buffalo Mountain wind farm near Oak Ridge, Tennessee.40

What draws bats to turbines is uncertain. Some experts assume that they come to feed on insects congregating in the clearings surrounding turbines; a related hypothesis is that the insects themselves are lured by the heat given off by turbine machinery. The mechanical or aerodynamic sounds that turbines produce may also appeal to bats. And then there’s the possibility that bats confuse turbines with tall trees suitable for roosting.41

Whatever the attraction, bats are killed by wind turbines in two primary ways, as evidenced by carcass surveys. Some collide with rotors; apparently the radar that normally guides bats’ flight has trouble detecting blades in motion. Most deaths don’t result from collisions, however. Roughly 90 percent of bats are killed by internal hemor-rhaging, or barotrauma, caused by the rapid changes in atmospheric pressure that occur within the vortices of spinning blades.42

While no recorded deaths of threatened or endangered bat species have been linked to turbine operations,43 the development of one wind energy project—the Beech Ridge Wind Farm in Greenbrier County, West Virginia—has been curtailed to prevent possible harm to the Indiana bat, listed as endangered since 1967. The Indiana bat is tiny, weighing about a quarter of an ounce and with a body 1.5 to 2 inches long. Its habitat extends across much of the East and Midwest, though its numbers have dropped by more than 50 percent since it was first listed as endangered. During the warmer months, Indiana bats live in wooded and semiwooded areas, roosting under tree bark and in dead trees. In winter, they hibernate in caves.

Beech Ridge Energy LLC, a subsidiary of Invenergy, announced plans to build its wind farm along a 23-mile stretch of Appalachian ridgeline in November 2005. As part of the project preparations, a consultant examined caves and conducted mist-net surveys to check for the possible presence of Indiana bats in the area. The consultant’s reports showed three caves currently used by hibernating Indiana bats between 5 and 10 miles from the project site, but none within 5 miles of the site. No Indiana bats were captured by the nylon-mesh mist nets, strung up like badminton nets at multiple locations. Based on

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