Wind turbine pressure change kills bats, research may help prevent future deaths
By CHRISTINE PETERSON Casper Star-Tribune | 28 October 2012 | billingsgazette.com
By CHRISTINE PETERSON Casper Star-Tribune | 28 October 2012 | billingsgazette.com
SHIRLEY BASIN, Wyo. – Catching bats requires long poles, water, yards and yards of super-fine netting and patience.
Bats are agile, fast and can pinpoint and catch something as tiny as a gnat.
Zoologists Doug Keinath and Ian Abernethy stood in fishing waders and layers of clothes the last night of July. They stretched mist nets over sections of the Medicine Bow River in southeast Wyoming, and the fabric created a black wall about eight feet high.
Bats began to fly as light faded. Some clearly avoided the net, others swooped down to skim the water and stumbled. Their feet and hands stuck to the fine netting like Velcro.
Any bats caught in the net would tell the scientists something.
Miles away, wind turbines sat motionless in the windless night. Their spinning blades can be deadly to bats, bursting capillaries in their lungs before the blades hit their tiny bodies. Three Wyoming bats are particularly susceptible when they migrate from summer to winter ranges.
Keinath and Abernethy were looking for bats to tell them which, if any, species called the area home. Land managers can use that information to negotiate where turbines are placed and even when they run to prevent more casualties.
What could be the largest wind project in the country has already been approved for the Sierra Madre Range just south of Shirley Basin, about 75 miles from this river. Bat movement could help determine where facilities and individual turbines go in relation to water and popular bat roosts.
“Maybe we could know that this drainage wouldn’t be great for wind turbines because of the bats that live here,” Keinath said. “That would be more than we know now.”
Deadly change
It’s called barotrauma and scientists only now understand how it works.
Wind turbine blades rarely hit bats as they do birds. Instead, bats fly near the spinning blades, and the change in pressure ruptures capillaries along the edges of their lungs. Their lungs fill with fluid, causing them to drown, said Keinath, a senior zoologist with the Wyoming Natural Diversity Database.
All bats are susceptible to barotrauma, but in Wyoming, wind turbines seem primarily to kill the silver-haired, hoary and eastern red bats. Those are also Wyoming’s only tree-roosting, migratory bats.
“It’s like a funnel cloud of low pressure,” Keinath said. “They can detect the blades but not the pressure and it damages their lungs.”
Lack of research means scientists don’t know exactly how many bats are killed by turbines, but estimates range from very few in some areas to up to 70 bats per megawatt of energy per year, Keinath said.
Most turbines generate about 2.5 megawatts of energy. That’s roughly 175 bats killed per wind turbine per year.
“That can quickly become thousands of bats a year,” Keinath said. “But there is a difference from wind farm to wind farm and even between wind turbines.”
Part of the reason scientists know so little is because dead bats are very hard to find at the base of wind turbines. Their fragile bodies are snatched up by other predators or camouflaged in the prairie.
Researchers first documented bat deaths in Australia, and in 1999, workers found 45 dead bats below turbines in Carbon County, according to a 2012 report by the U.S. Geological Survey.
Zoologists worry about deaths because bat populations rely heavily on adult survival. They generally have one pup per year, unlike other small mammals such as deer mice, which may have between 20 and 99 babies each year, Keinath said.
While other scientists continue trying to monitor bat deaths, researchers with the Natural Diversity Database are trying to document where the three species of bats live in Wyoming in hopes of preventing future deaths.
More like lions
Monitoring bat movement includes hours of sitting in the dark punctuated by brief periods of activity. On July 31, a futuristic-looking device, called an AnaBat, sat on a small camp stool making clicking sounds. It recorded the frequencies of each bat’s echolocations, helping identify the species. Each bat species has a unique echolocation, just like a bird has its own song.
In Wyoming, only spotted bats can echolocate at a frequency audible to humans. They sound like two pebbles knocking together.
Keinath and Ian Abernethy, assistant zoologist for the Natural Diversity Database, took turns checking the nets every 15 minutes for signs of bats. Abernethy found the first one.
He detangled it from the fine netting and placed it in a small cotton bag. The bat chattered like an angry chipmunk.
“Bat 1, net 1, the time is 21:10. It’s a female and an adult,” Abernethy said, recording the bat’s data in a log book under the glow of his headlamp.
“It’s probably a little brown bat,” Keinath said, referring to the bat’s species.
It weighed 0.3 ounces, slightly more than three pennies.
Keinath untangled a second bat while Abernethy finished examining the first one, looking at its wings for sign of the deadly white-nose fungus and measuring its ear length.
The scientists worked quickly. If bats remain motionless for too long in the cold, they can fall into a state called torpor, which is a temporary hibernation. On a cold night, it may take too much energy to warm back up and fly away. Keinath warmed the second bat, still inside the cotton bag, by holding it inside his coat.
His co-workers sometimes call him Batman. He started studying bats in Yellowstone National Park 10 years ago in his first post-graduate project with the University of Wyoming. He has continued his work through the Wyoming Natural Diversity Database.
“Biologically, they are fascinating animals,” Keinath said. “They’re tiny, but they have more in common with mountain lions than mice.”
Bats are carnivores, reproduce slowly and are long-lived, unlike many other small mammals, he said.
He admires their long lives. He caught a bat once in Fort Laramie that had been banded 14 years before. They’re hard to catch and hard to study.
They control insects so well that some studies have shown how much pesticide use would increase in agricultural areas if bats were eliminated.
“From my perspective, I feel every critter out there has an intrinsic value,” Keinath said. “A bat has as much value as a deer or an antelope.”
They’re the top of their food chain, susceptible only to diseases and human activity.
That’s why this study is so important, Abernethy said.
Instead of trying to bring bat species back from the brink if their numbers plummet, this information could perhaps prevent bats from dying in the first place.
A study for the future
Scientists with the Bureau of Land Management agree. They want to know where bats live and when they move as the department’s land managers begin permitting more turbines.
“We want the biological information for us or anybody to use,” said Dennis Saville, a wildlife program manager for BLM in Cheyenne.
They focused on southern Wyoming to coincide with the bulk of Wyoming’s wind energy production.
The bat study is finishing its second of three years. The $204,000 price tag comes out of the BLM’s renewable energy project.
Ultimately, Saville hopes the information will work into the permitting process for new turbines, either changing their locations or when they turn.
If researchers find bats eat or roost more near certain waterways, for example, turbines may need to go somewhere else. If hoary bats migrate most heavily during a certain time of year, land managers may see if it’s possible to turn off turbines or reduce their speed, he said.
Mitigation for possible bat conflicts is part of the environmental impact statement for the proposed Chokecherry and Sierra Madre Wind Energy Project in southeastern Wyoming. At 1,000 turbines, it would be the biggest wind energy project in the country. Construction could begin as early as 2013, according to the developer’s website.
A spokesperson for Power Company of Wyoming, the Chokecherry developer, referred questions to the Bureau of Land Management.
Land managers will work with the power company during siting of turbines to work around high bat use areas, Saville said. The company will also be required to monitor the turbines and their impacts on bats.
“We won’t stop all the impacts of the turbines, but we can reduce them,” he said.
Not a popular place
Not many bats moved through Keinath and Abernethy’s spot on the Medicine Bow River. But, when surveying possible bat locations, finding few bats is as useful as discovering hundreds, Keinath said.
The scientists caught only three bats in their nets, all little brown bats, one of Wyoming’s most common species. They will likely mark the spot on their map as having relatively low bat activity.
The study continued in southeast and central Wyoming throughout the summer and the fall migration season. Four field researchers worked in teams of two and stayed on the prairie more than a week at a time.
By 1 a.m. on the last day of July, most bats had eaten and were resting. Little brown bats consume almost their entire body weight in food each night.
Keinath and Abernethy began taking their nets down. Bats would feed again, but not until shortly before sunrise. As supervisors of the project, the scientists would have to work during the day analyzing the gathered data.
But they would be back out in the field again, waiting for the sun to set.
URL to article: https://www.wind-watch.org/news/2012/10/29/wind-turbine-pressure-change-kills-bats-research-may-help-prevent-future-deaths/