Wind turbine and bat mortality

At sunset June 22, 2005, installation was complete on our 1-kilowatt Bergey wind generator. We watched as our first wind-generated electricity began to flow. That task had been completed. The next, less strenuous but more time consuming task, then began.

For more than 20 years, people have been concerned about bird mortality caused by wind generators. Altamont Pass, Calif., where 1,000 birds of prey died annually, was of special concern. Red-tailed hawks, kestrels and golden eagles, all of which fly toward moving objects, met their doom at the wind farm. Despite the large numbers that died there, it has been estimated that one of 5,000 to 20,000 bird deaths is due to collisions with wind turbines. The average annual bird mortality in the U.S. has been calculated as 1.83 per turbine.

As wind power grew more popular, the concern spread to bats. Recently, a University of Maryland graduate student began a study of bird mortality at a West Virginia wind farm. She expected to see a few dead birds whacked by the blades. But what she found shocked her—hundreds of battered bat carcasses lay on the ground. She and other researchers estimate that between 1,500 and 4,000 bats died there in 2004. Similar bat deaths were recorded at a Pennsylvania wind farm. Most of the mortality occurs in bat migration routes.

No one is sure what attracts bats to the towers. Are they attracted to the spinning blades? Does the sound frequency of the whirring blades attract them? Are the towers placed too close to bat colonies? Does weather have anything to do with it?

Although concern for bat mortality at wind farms has grown, until last year no studies of bat mortality caused by small, home-sized wind turbines had been done. We contacted Bat Conservation International to offer our help in obtaining data.

We have a bat colony in our barn less than 100 feet from the wind tower. At dusk, at least 215 little brown bats pop erratically into the air to begin their night’s work of catching insects. Exiting one or two at a time, they head east, then west, into the sky. Observing them is a special experience that we share with guests. Having them so close to the wind generator seemed quite unique. We felt this would be a likely site for a study.

We were given instructions about proper research techniques. At sunrise, we were to systematically examine the ground under the tower. The diameter of the area was 10 times the diameter of the generator’s blades.

We marked four quadrants: northeast, southeast, southwest and northwest. Early each morning, we walked to the tower and began our daily count. We paced a 3-foot wide transect in each of the quadrants, carefully observing the ground. We recorded wind and weather conditions to correlate with numbers of bats found.

At the end of the season, we tallied the number of bats found as well as the number of birds (some were seen briefly sitting on guy wires). Our total for the year was zero.

Although we had no numbers to enter into the sophisticated formulas, we feel we do have at least one conclusion: the first Small Wind Bat Mortality Study revealed that home wind generator-caused bat mortality is not a problem at our site.

From the May 24-30, 2006, issue

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