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Wind turbines have killed more than a million bats in the northeastern United States since 2006.

The butterfly effect suggests the flapping of a tiny insect’s wings in Africa can lead to a tornado in Kansas.

Call this the bat effect: A bat killed by a wind turbine in Somerset can lead to higher tomato prices at the Wichita farmers market.

Bats are something of a one-species stimulus program for farmers, every year gobbling up millions of bugs that could ruin a harvest. But the same biology that allows the winged creatures to sweep the night sky for fine dining also has made them susceptible to one of Pennsylvania’s fastest-growing energy tools.

The 420 wind turbines now in use across Pennsylvania killed more than 10,000 bats last year — mostly in the late summer months, according to the state Game Commission. That’s an average of 25 bats per turbine per year, and the Nature Conservancy predicts as many as 2,900 turbines will be set up across the state by 2030.

This is a bad time to be a bat.

It may seem like a good thing to those who fear the flying mammals, but the wind farm mortality rate is an acute example of how harnessing natural energy can lead to disruptions in the circle of life — and the cycle of business. This chain of events mixes biology and economics: Bat populations go down, bug populations go up and farmers are left with the bill for more pesticide and crops (which accounts for those pricey tomatoes in Kansas).

Wind industry executives are shelling out millions of dollars on possible solutions that don’t ruin their bottom line, even as wind farms in the area are collaborating with the state Game Commission to work carcass-combing into daily operations.

“If you look at a map and see where the mountains are, everything funnels through Somerset,” said Tracey Librandi Mumma, the wildlife biologist who led the March commission report on bird and bat mortality. “If I’m out driving … I wonder, ‘How many are being killed at that one?’ “

Bats are nature’s pesticide, consuming as many as 500 insects in one hour, or nearly 3,000 insects in one night, said Miguel Saviroff, the agricultural financial manager at the Penn State Cooperative Extension in Somerset County.

“A colony of just 100 little brown bats may consume a quarter of a million mosquitoes and other small insects in a night,” he said. “That benefits neighbors and reduces the insect problem with crops.”

If one turbine kills 25 bats in a year, that means one turbine accounted for about 17 million uneaten bugs in 2010.

Bats save farmers a lot of money: About $74 per acre, according to an April report in Science magazine that calculated the economic value of bats on a county-by-county basis.

In Allegheny County, bats save farmers an estimated $642,986 in a year. That’s nothing compared with more agricultural counties in the region such as Somerset ($6.7 million saved), Washington ($5.5 million) or Westmoreland ($6.1 million).

Lancaster County? You owe bats $22 million.

In all of Pennsylvania, bats saved farmers $277.9 million in estimated avoided costs.

Initially, the “Economic Importance of Bats in Agriculture” article was meant to attract attention to the white-nose fungus virus that is wiping out entire colonies of bats across the country.

“We were getting a lot of questions about why we should care about white-nose syndrome,” said author Justin Boyles, a post-doctoral fellow in bat research at the University of Tennessee. “Really, it’s the economic impact that makes people listen.”

The white-nose syndrome is compounding the wind turbine problems, having killed more than a million bats in the northeastern United States since 2006. It surfaced in Pennsylvania in 2008 and has killed thousands of in-state bats.

Meanwhile, the same creatures that save Pennsylvania farmers millions of dollars each year are also costing energy companies some big bucks as they try to stave off a mass execution beneath the blades.

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