After undergoing sleek upgrades over the past two decades, the iconic wind turbines at Altamont Pass are killing a lot fewer birds.
But they’re still claiming the lives of another important creature of the sky: bats.
As wind farms become an increasingly important source of clean energy, there are growing concerns among scientists about what all the new spinning blades will mean for bats – particularly the hoary bat, the most widespread migratory bat species in North America.
The controversy is a sobering reminder that the nation’s ambitious efforts to combat climate change will often come with environmental trade-offs and agonizingly difficult solutions.
Winifred Frick, a UC Santa Cruz bat ecologist, estimates that without aggressive intervention to reduce the number of bat deaths, North America could lose up to 90% of hoary bats to wind turbines over the next 50 years.
“We should be seriously concerned,” said Frick, who is also the chief scientist at Bat Conservation International, a nonprofit based in Austin, Texas. Her peer-reviewed research on hoary bat turbine deaths has been published in the journal Biological Conservation.
Capturing powerful winds off the Pacific, the Altamont Pass Wind Resource Area is a 37,000-acre zone stretching across the tawny hills of eastern Alameda and Contra Costa counties. The wind farm’s construction in the early 1980s marked the beginning of a new era of alternative energy.
Wind energy is integral to our nation’s shift away from planet-warming fossil fuels. The U.S. Energy Information Administration says that 8.4% of the country’s utility power now comes from wind energy. Many energy experts expect that percentage to double by the end of the decade.
When the Altamont wind farm’s turbines first began churning out electricity decades ago, environmentalists were alarmed that hawks, eagles and other raptors were being killed by the giant blades.
After conservation groups filed suit, the wind farm’s owners hired environmental consultants and began replacing older equipment with taller, larger turbines to reduce raptor deaths.
It worked. Independent research showed that turbine-caused deaths of the American kestrel, burrowing owl, golden eagle and red‐tailed hawk were cut in half from 2005 to 2010.
Migratory bats, however, are continuing to die en masse.
In the United States alone, wind turbines are estimated to kill at least half a million bats annually, according to Michael Whitby, a biologist and data analyst at Bat Conservation International. The group says numerous species have been found strewn beneath wind turbines, including the Eastern red bat, silver-haired bat and hoary bat.
Already threatened by deforestation, hoary bats are the most common casualty, accounting for over a third of bat carcasses found beneath turbines, Frick said.
Most of the deaths occur at night when the nocturnal bats alight from their tree roosts and cruise through the sky in search of an insect meal.
“They’re very easy to fall in love with,” said Katrina Smith, an environmental scientist with the California Department of Fish and Wildlife. “They fly really far to migrate and they have just two pups a year. They’re worth protecting.”
With its lush salt-and-pepper fur, the hoary bat has been called the “George Clooney of the bat world.” But more importantly, scientists say, bats play starring roles in a harmonious and diverse ecosystem. They’re one of the few nighttime insect predators, scientists note, helping to maintain an ecological balance in the sky by feasting on moths and mosquitoes.
“Their value of being on the planet is that they’re part of biodiversity,” Frick said. “They have a right to exist.”
No one knows how many hoary bats there are. Because the solitary creatures roost in trees, researchers can’t count them as easily as they do cave-dwelling bats – and they’re tricky to catch and track because of their lengthy flight paths. In autumn, hoary bats migrate south to roost and mate, which is when most turbine deaths occur.
It’s also been difficult for researchers to determine the number of hoary bats being killed by the turbines.
Ecologist Ted Weller of the U.S. Forest Service said the bodies of bats are small and difficult to find. Their mottled silver and brown fur strongly resembles a dead leaf. And with their wings curled around them, they’re about the size of two thumbs. They also decompose quickly and are often snatched by scavengers.
“We know we’re not seeing all of the carcasses,” Weller said.
When they find and inspect dead bats, ecologists often see the bruising or broken wings that are indicative of a run-in with a turbine. Scientists say they can also be whacked to the ground by the air pressure of a spinning blade, which is the size of three semi-truck trailers.
Although from afar the turbines appear to move relatively slowly – sometimes making only eight revolutions per minute – the tips of the blade are moving nearly 180 miles per hour. That’s too fast for a curious bat to get out of the way.
Virtually no conservationists are arguing that wind turbines should be torn down. But they contend that slight tweaks to turbine operating practices could help prevent thousands of bat deaths.
Because hoary bats are most likely to be active when winds are gentle, bat experts say, cutting operations on nights with low winds can reduce bat deaths at a modest cost to turbine companies.
Restricting the speed at which the turbine blades start up, particularly in the fall, would allow bats to come and go at their peak flying hours without the risk of colliding with a moving blade, some biologists argue. One 2010 study published in the journal Frontiers in Ecology and the Environment concluded that such curtailment could halve the number of bat deaths while decreasing the annual profit of wind farms by only 1%.
Some bat ecologists say that because the animals use sound waves to interpret their surroundings, ultrasonic noises from turbines could potentially deter bats. But research on sound deterrents is still in its infancy.
With more research and the cooperation of the wind industry, biologists say, it should be possible to strike a balance between wind development and bat preservation.
In a statement to the Bay Area News Group, Stu Webster, a senior official with the American Clean Power Association, said the industry is working with the U.S. Department of Energy, bat experts and conservation groups to reduce the number of bat fatalities.
“We are making progress to better understand bats and wind energy,” Webster said.
“We can have wind turbines and bats,” Frick said. “I think that finding ways to operate wind turbines in a way that protects biodiversity and prevents extinctions of bats is part of our commitment to sustainable renewable energy and our fight against climate change.”
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