Bat Species Faces Serious Threats from Wind Farms

North America’s hoary bats could be spiraling toward a massive decline unless efforts are made to reduce fatalities at wind farms, a new study reports.

Without intervention and conservation efforts to lower deaths, hoary bat populations could drop by 50% by 2028, researchers found.

“We have been concerned about hoary bats for some time, but this research emphasizes how urgently we need to act to implement known solutions,” study co-author Winifred Frick, chief scientist for Bat Conservation International, tells Treehugger.

Hoary bats (Lasiurus cinereus) are relatively large bats, weighing between 20-35 grams (0.7-1.8 ounces). They have distinctive dark fur that is dusted with white which makes them look frosted or hoary, which is how they got their name. They also have a yellow patch on their throat and dramatic two-tone patterns on their wings.

They are found throughout most of North America and into Central America. They prefer to roost alone in trees where they will hang from a branch, wrapped in their furry tail membranes.

“Hoary bats undergo seasonal migration, moving from summer ranges across most of North America to southern and coastal winter habitats. Hoary bats will also hibernate for short periods of time,” Frick says.

“Hoary bats in North America provide vital ecosystem services such as insect pest consumption. The economic value of insectivorous bats to U.S. agricultural industry has been estimated in the billions annually.”

Wind Energy Expansion

For their research, Frick and colleagues created models of species population growth and mortality. They considered two wind energy build-out scenarios—high and low—which looked at the anticipated growth of the wind energy sector in the United States and Canada through 2050.

The report focused on determining how wind energy expansion might affect hoary bat mortality and what industry solutions could be put in place to help.

"If conservation actions are implemented broadly and rapidly, the risks of further decline and extinction may be avoided,” says Frick.

“The good news is we already know how to reduce bat fatalities. What this study emphasizes is just how quickly we need to implement those solutions before it is too late. Hoary bats are found almost everywhere across the U.S. and Canada, so our findings have implications for wind projects across the continent.”

Conservationists and Industry Working Together

Researchers and conservation biologists have been concerned about the number of bats killed at wind farms for more than a decade, Frick says.

“In 2014, the U.S. Fish and Wildlife Service conducted an expert elicitation with bat biologists to inform efforts to determine the population-level impact of fatalities at wind turbines to the hoary bat. That effort led to a paper published in 2017 describing the potential and likelihood that fatality rates could cause declines of the hoary bat population in North America,” Frick says.

“The new research builds on that effort by looking at projected growth in wind energy developments and answering key questions about how much fatality reduction is needed to protect hoary bats, so that we can achieve sustainable wind energy and protect biodiversity.”

Bat Conservation International has been working with the wind industry to test methods of lowering bat fatalities, Frick says.

“One of the most promising and proven solutions is turbine curtailment, which slows down or stops the rotation of turbine blades during narrow windows of time, such as at night during fall migration and under low wind conditions when energy production is lessened.”

According to the group, the best evidence so far suggests that turbine curtailment below five meters per second could reduce hoary bat fatalities nearly in half.

Hoary bats are now beginning their long-distance migrations to warmer climates, which is when they are especially vulnerable to colliding with rotating blades of wind turbines.

“We recognize wind energy as a critical part of the fight against climate change,” says Frick. “By working collaboratively with industry partners, we can have sustainable wind energy while protecting biodiversity.”