Volume 36
Issue 2

Whats long been suspected is now being confirmed: wind turbines can have serious, rapid impacts on entire bat populations. Collaborative research led by BCI Senior Director of Conservation Science Winifred Frick puts fresh urgency into the need to pursue a workable solution, and at least one bat species survival may depend on it.

Bat flying in the sky
Dead hoary bat next to a turbine
Courtesy of Michael Schirmacher

A new study that looked at hoary bat (Lasiurus cinereus) fatalities at wind energy facilities revealed the population of this species may plunge by a staggering 90 percent over the next 50 yearseven if no new turbines are built.

For the study, the first of its kind, international experts, academics and biologists from several federal agencies came together to better understand whether fatalities from wind turbines may be causing large-scale species declines. Using a range of estimates of hoary bats reproduction and survival rates, and by comparing those figures with estimated fatalities at wind turbines, the authors of the study described a variety of possible species-level impacts.

The study used conservative figures of bat fatalities128,000 hoary bat fatalities annually in the U.S. and Canadaand assumed no new wind turbines are to come online in the future. They found, with the highest-possible population estimate of 10 million hoary bats, the species could still experience a 50 percent decline over the next 50 years.

With a more conservative and likely population estimate, around 2.5 million individuals reproducing at a more plausible rate, that impact intensifies to a 90 percent decline within the next five decades.

But wind energy is only growing, producing 5 percent of todays electricity generation in the U.S. and Canada, and its expected to triple by 2050.

Bat flying in the sky
Wind energy research with USGS and BCI
Courtesy of Michael Schirmacher

Frick, the lead author of the study, said the findings underscore the need for immediate action.

We should be concerned about our migratory bats that have high levels of fatality from wind turbines, Frick said. Its a wake-up call for thinking about the impact on other migratory bats as well.

But bats being bats, they are hard to find and even tougher to follow around. Researchers rely on existing and emerging technologies to track, observe and even repel bats from wind turbines. BCI continues to partner closely with wind industry companies to find solutions to producing wind energy that can be simultaneously bat-friendly but also economically sensible.

Shifting Practices

Bats natural curiosity about their environment does not serve them well when it comes to turbines. Michael Schirmacher, BCIs Wind Energy Program Manager, said from analysis of infrared video of bats investigating the airspace around turbines, its clear they have no inkling of their jeopardy.

Its not a learning experience, unfortunately. One hit is all it takes, Schirmacher said.

Since the first reports of thousands of dead bats at a wind energy facility in West Virginia in 2003, BCI has been deeply involved over the last decade to understand the causes, and with the help of partners in government and the wind industry itself, to develop mutually beneficial strategies.

BCI field technicians collect data on a bat carcass
Courtesy of Cris Hein

Research, spearheaded by the Bats and Wind Energy Cooperative (BWEC), a research consortium of government, industry, academia and non-profit partners including BCI, has focused on ways to reduce bat fatalities at wind turbines. So far, the most effective method is to employ a strategy known as operational minimization, alternatively known as curtailment. Dozens of studies have shown that bat fatalities could be reduced from 44 to as much as 93 percent just by limiting the rotation of the blades during narrow windows of time when bats undergo autumn migrationat night, under low wind conditions, from late summer through early autumn.

Bats tend to be killed more often at low wind speeds, blowing at 11 to 13 miles per hour, and many turbines dont even begin to push energy into the grid until winds pick up to near those speeds. Moreover, the majority of fatalities take place during the warm nights of autumn migration. Rotating turbines out of the prevailing wind, or angling the rotor blades parallel with the breeze until wind speeds are slightly higher, can significantly reduce fatalities.

In late 2015, the American Wind Energy Association (AWEA) announced a voluntary program for its members that aimed to reduce bat fatalities by about 30 percent. This best management practice was the first of its kind for the industry and showed its awareness of the severity of the impact wind turbines have on bats.

Participation has been widely implemented by the wind industry, yet additional measures are needed. A great deal of the work BCI has been pursuing in recent years entails a better understanding of how, why, where, when and which species of bats are killed at wind facilities, to minimize fatalities and maximize wind energy production.

Though the reduction of electrical generation capacity caused by curtailment varies by market, some studies peg the loss of capacity at anywhere from 1 to 3 percent.

[Curtailment] is an example of the industry stepping up and finding a way to reduce impacts while not unduly impacting the economics of wind, said Tom Vinson, vice president for federal regulatory affairs for AWEA.

Cris Hein, Director of BCIs wind energy program and Program Coordinator for BWEC, affirmed that efforts are underway to devise even more specific recommendations to minimize reductions in electricity generation. But it requires much more informationincluding details like the exact time of night bats interact with wind turbines, weather data, such as temperature and barometric pressure, and exact wind speeds and direction.

Hoary bat with GPS tag
Courtesy of Cris Hein

The wind industry has a legacy of care for the environment, said Peter Kelley, AWEAs vice president for public affairs. We recognize that its important to continually work to reduce any impacts we do have, while keeping this as a major solution to the countrys need for clean energy.

We do have a collaborative relationship with the industry, and this is an opportunity to work with them to find a solution, Hein added.

The industry agrees with conservation organizations, like BCI, that advancing the science and working to answer the questions are valuable, to the extent that there are impacts to mitigate, Vinson said.

Tech Solutions

There is some evidence to suggest that some species of bats are attracted to something about the wind turbines themselves, but what that is, if anything beyond sheer curiosity, remains unknown. Innovative new technologies, as ever in the bat world, are necessary to illuminate their cryptic behaviors.

One promising solution Hein and Schirmacher are investigating is the effectiveness of turbine-mounted ultrasonic acoustic deterrents, designed to jam bats echolocation or make the airspace around the turbine aurally uncomfortable.

Understanding how bats approach and use the airspace around wind turbines is another key area of research as well. GPS tags have finally gotten small enough to be attached to bats, albeit larger species, so that researchers can track bats movements more closely during migration and nightly foraging.

High-resolution thermal security cameras are also allowing BCI and its research partners to better see what even tiny 12-gram bats are doing at night around the turbines, Schirmacher said. The U.S. Geological Survey has been a key partner in this work, and in developing software to help streamline analysis of the resulting footage.

By comparing video data with environmental information already being collected by the turbines themselveswind speed, humidity and temperatureresearchers can pinpoint which bats are dying, when and where, and under what conditions, to even further define dangerous conditions for bats.

For many years, we were limited in our ability to relate fatalities to specific conditions. If we found a dead bat underneath a wind turbine and we identified it as dying the previous night, we could only relate that fatality to the nights average weather conditions, Hein said. Now, with the use of infrared cameras, we can record the exact time of night, specific weather conditions and area of the wind turbine where interactions occur. It has really opened the door to a better understanding of the behavior of bats around wind turbines.

Though the outlook at the moment is grim for the hoary bat and other migratory species, there are many paths and possibilities moving forward.

We have the goal of working collaboratively to resolve this issue that meets everybodys needs, Hein said. Not only BCIs goals of protecting bats, but also in being able to generate renewable electricity. We have our work ahead of us.