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Texas is the No. 1 wind energy state, but what’s the effect on bats and birds?

By Russell Roe
On a muggy September morning in South Texas, Sara Weaver heads out on a morbid quest just as the sun starts to peek over the horizon, knowing the day will soon become unbearably hot. She’s sweating already. Above her, the massive blades of the turbines at Duke Energy’s Rio Grande Valley wind farm turn slowly in the South Texas breeze. Before long, she finds what she’s looking for — the carcass of a Mexican free-tailed bat.

The bat was on its way back to Mexico after spending the summer in Texas, most likely in one of the Hill Country’s limestone caves. Millions of bats had started their migration southward. This one was flying around the wind turbine — bats are thought to be attracted to the turbines — when the blade swung around and struck it dead.

Weaver stoops down and records the bat’s location, sex and species. She puts it in a plastic bag and resumes her search for more fatalities, knowing that some carcasses might have already been carried away by coyotes, caracaras or other scavengers.

“It’s rough,” Weaver says. “It’s very tedious day in and day out, staring at the ground looking for carcasses, in very difficult conditions with the heat and humidity. But the overarching goal of the project keeps everybody upbeat, knowing that why we’re out there is to reduce these impacts and keep more of these bats flying around out there and alive.”

Weaver, a biology lecturer at Texas A&M University-San Antonio and a doctoral student at Texas State University, has been given unprecedented access to this wind farm, and her research into acoustical deterrence for bats may prove to be a lifesaver for the flying mammals while also providing some of the first clues about how wind energy affects Mexican free-tailed bats.

Wind energy’s fatal toll on birds has been documented since the first turbines popped up in the 1980s. Wind farms also kill bats. In fact, bats are killed in greater numbers than birds at wind energy plants across the country.

The wildlife deaths paint a more complex picture for wind.

“Wind does create a significant amount of energy for us, as well as jobs,” Weaver says. “It is considered a renewable energy resource and has some benefits such as lower water use and carbon emissions. But unfortunately, an unintended side effect has been fatalities of birds and bats.”

Texas is right in the middle of it all, with high stakes for wind energy and wildlife. Texas has the greatest number of wind turbines in operation, the largest population of bats in the country and the nation’s highest diversity of bird species.


Birds and bats

Birds die from collisions with wind turbines, but wind energy's toll on birds pales in comparison to other human-caused sources of bird mortality. Wind turbines are estimated to cause 234,000 bird deaths per year in the U.S., according to statistics compiled by the U.S. Fish and Wildlife Service, whereas building strikes cause 600 million bird deaths per year, and domestic cats are blamed for 2.4 billion bird deaths per year.

Still, the bird deaths are a source of concern as wind energy expands into areas where wildlife is already experiencing declines from habitat loss and other stressors, and wind energy’s effects on notable species such as raptors can be problematic.

The National Audubon Society supports wind power as a renewable energy source that helps reduce the threats to birds caused by climate change, which it considers to be the biggest danger to North American birds. It stresses that wind power facilities need to be operated in ways to minimize harm to birds.

The story is more distressing for bats. More than 600,000 bats are killed by wind turbines each year in the United States. Bats are facing a double whammy as white-nose syndrome wipes out bat populations in the eastern part of the country.

“Birds got the most attention at the beginning,” Weaver says. “In the past decade, researchers and the industry have found that bats are actually killed at higher numbers than birds in most circumstances.”

A 2017 study by a Bat Conservation International senior scientist found that the population of the hoary bat — the species most frequently killed by wind turbines in the U.S. — could plunge by 90 percent over the next 50 years if no action is taken to curb mortality.


Bats and wind

No one was even looking for bats under turbines until 2003, when a series of alarming fatalities were reported in West Virginia. Since then, bats have moved to the forefront of conservation concerns for wind energy.

The majority of U.S. fatalities reported to date have occurred in three migratory tree-roosting species: the hoary bat, eastern red bat and silver-haired bat. Collectively they make up 70 percent of reported bat fatalities. However, little data has been available from the southwestern United States, where species such as the Mexican free-tailed bat are widespread. Weaver is trying to change that.

Texas is the battiest state in the country, with the greatest diversity of bat species and some of the world’s largest colonies. On warm summer nights, millions of Mexican free-tailed bats emerge from limestone caves across the Hill Country in concentrations dense enough to show up on weather radar.

Bat fatalities at wind farms have been shown to peak during fall migration. Weaver conducted two years of studies at Duke Energy’s Los Vientos wind facility in the Rio Grande Valley during fall migration to test the effectiveness of ultrasonic acoustic deterrents in reducing bat deaths.

The deterrents she tested reduced bat fatalities by 50 percent.

The devices are designed to “jam” a bat’s echolocation by creating a disorienting space around a turbine.

“The idea is that the sound created by the units would interfere with the bats’ ability to echolocate in that airspace,” Weaver says. “If the bats are foraging around the turbines or communicating with one another, this sound would disrupt their ability to do so and force them out of the area.”

Bats do a pretty good job of avoiding crashes with tall, human-made structures like communications towers. Why are they falling victim to turbines? For unknown reasons, they appear to be attracted to the turbines, possibly for roosting or foraging.

In Weaver’s study, 16 turbines were equipped with the deterrents. Each night, eight turbines were randomly selected to employ the deterrents, while the other eight operated without them. In the morning, carcass searches were conducted under all 16 turbines.

Her second year of testing, done in the fall of 2018, produced similar results, with the deterrents reducing fatalities for Mexican free-tailed bats, hoary bats and other species.

Her research, done in collaboration with Bat Conservation International, is also providing some of the first scientific data on wind energy’s effects on Mexican free-tailed bats.

She found that the free-tailed bats accounted for 77 percent of the deaths.

“We are seeing higher rates of fatalities for Mexican free-tailed bats than for any other species,” she says. “Most of the previous studies have been outside free-tailed bat range. In areas such as Texas where there are high numbers of that species, we anticipate seeing higher impacts."

Photo © Sarah Perry

Sara Weaver trains crew members on the sampling protocol when a dead bat is found at a wind turbine.


Photo © William Ramirez

Acoustical deterrents are mounted on wind turbine towers at the Los Vientos wind facility.


Birds and wind

Wind energy got off to a rocky start in the 1980s when the Altamont Pass wind farm, one of the first extensive wind power developments, was built in California in an area with large numbers of raptors along a major bird migratory route. The industry has learned a lot since then about proper siting of turbines.

Most of the birds killed by wind turbines in the United States are songbirds. Current fatality rates (three to six birds per megawatt per year, according to most studies) do not appear likely to lead to population declines in most bird species, according to the American Wind and Wildlife Institute, a nonprofit founded by the wind industry and conservation organizations.

“We have enough data that looks like wind energy is not going to be the proverbial nail in the coffin for songbirds,” says Amanda Hale, a biology professor at Texas Christian University who studies wind energy.

Golden eagles and other raptors continue to be a concern, with a potential for long-lasting impacts.

“Golden eagles are an apex predator,” says Clint Boal, a professor at Texas Tech University who studies the effects of wind energy on raptors. “Nothing really messes with a golden eagle. They occur at low densities, are long lived and have huge home ranges. Mortality caused by humans has the potential to have a population-level effect. Because they often occupy these areas where we like to put wind turbines, you have a potential conflict.”

Using a team of climbers to rappel down to eagle nests on cliffsides in Texas, Boal has been tagging golden eagles to track their movements.

Of the 150 golden eagles tagged by Boal and colleagues in the western U.S., none have been killed by turbines in Texas, though one was killed just across the border in New Mexico. Fatalities are higher in places like Wyoming and California with larger eagle populations.

In 2013, Duke Energy became the first wind company to face criminal prosecution for the deaths of birds protected under the Migratory Bird Treaty Act, including golden eagles, at two Wyoming sites. It has since installed a series of innovative computer-connected cameras designed to detect approaching eagles and shut down turbines if needed.

Grassland birds may not welcome wind energy either, but the results so far are mixed. What happens to birds that have evolved in wide-open landscapes when you start putting up big, vertical structures? A comprehensive, multiyear study of greater prairie-chickens in Kansas showed neutral, positive and negative responses to wind energy.

“It’s complicated,” Hale says. “It looks like wind is not universally bad on grassland birds.”

Research has shown that close proximity to trees, utility poles and oil platforms causes displacement of prairie-chickens, for example, but Hale has also found higher nest success for scissor-tailed flycatchers and dickcissels close to wind turbines, possibly because turbines offer some degree of protection from predators.

Boal and some of his fellow Texas Tech professors started doing prairie-chicken assessments in the Panhandle in the mid-2000s in anticipation of wind energy development, but he says the projects in Texas prairie-chicken habitat haven’t yet come to fruition. They continue to be concerned about future impacts, however, and are continuing to monitor wind developments and any negative effects on lesser prairie-chickens.


Here in Texas

Texas has abundant wind and a favorable regulatory climate, and that combination spurred a wind boom that started in 1981 and rolled across western Texas faster than a tumbleweed with a tailwind. Not even the speed trap in Estelline could slow it down. Texas is the No. 1 wind energy state, and wind may soon surpass coal as an energy source in Texas.

State, county and local governments in Texas have little control over where wind projects are located — that’s between the landowner and the developer. The Texas Parks and Wildlife Department has no official oversight over wind projects.

There’s little public data available on bird and bat deaths because companies don’t release that information. That makes it difficult to assess the real impact of wind energy on Texas’ wildlife.

“TPWD doesn’t have the authority to stop a project,” says Laura Zebehazy, TPWD program leader for wildlife habitat assessment. “Our role is to educate and provide science-based information to those wind energy developers and landowners who request it.”

West Texas and the Panhandle have been the historic heart of wind country in Texas, but South Texas has also witnessed the spread of wind power.

The development didn’t happen without opposition.

“There were some pretty nasty public meetings about wind energy,” says Russell Hooten, TPWD habitat assessment biologist. “People didn’t want them along the coast where we have the Central Flyway. They painted this picture of birds basically flying into a blender. We haven’t really seen that.”

Hooten says most of the wind companies in South Texas voluntarily consult with TPWD, and he says most comply with the U.S. Fish and Wildlife Service’s 2012 wind energy guidelines, which involve site evaluation for environmental impact and post-construction monitoring to document wildlife mortality. Wind companies and conservation groups agree that responsible siting of wind turbines away from areas with high wildlife activity is a key first step. TPWD is working on its own set of wind energy guidelines.

Wind energy is considered a renewable energy. Wind is clean, free and readily available, and it continues to grow as an energy source. The wildlife deaths associated with it are an unfortunate byproduct, TCU’s Hale says, and need to be weighed against the benefits provided by the technology.

“There are costs and impacts to wildlife from any energy source,” she says. “I’m really hoping the conversation will switch from ‘What about wind and what are the impacts from wind?’ to more of ‘OK, if we’re not getting electricity from wind, where do you want to get it?’ Would you rather have coal and all of those negative impacts, especially on human health? That’s a huge problem, but it just doesn’t seem like it’s treated in the same way as these wildlife impacts are.”


Russell Roe is the managing editor of Texas Parks & Wildlife magazine.

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