Wind turbines have killed 19 million bats in 40 years in the US

Wind turbines have killed nearly 19 million bats in the US over the past four decades, according to the most comprehensive analysis of its kind to date. The problem seems to have worsened in recent years, with more than 1.5 million deaths now occurring annually.

But there may be ways of making this green energy source safer for wildlife without overly affecting energy production. This data can help “advance research to really support effective conservation measures and science-driven decision-making in the future”, says Charles Labuzzetta at Fort Collins Science Center in Colorado.

Bats play a vital role in ecosystems, particularly by controlling insects like mosquitoes and moths that produce crop-killing caterpillars. But many species face growing threats from habitat loss, disease and human activities, with some now classified as threatened or endangered.

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Wind turbines are one of these human-activity threats. Researchers have previously found large numbers of dead bats at wind farms during monitoring that is required to comply with wildlife protection regulations. But not all wind farms share their results, and monitoring methods vary from site to site, says team member Bethany Straw, also at Fort Collins Science Center.

“We know bats are being impacted, but could we change the engineering or sites of a turbine to minimise those impacts?” she asks. “There’s been an increasing interest in this, but we just haven’t had the appropriate data yet.”

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Now, Straw, Labuzzetta and their colleagues have analysed 499 reports from wind farms across the 48 adjoining US states to estimate how many bats were killed by turbines from 1981 to 2024, focusing on 10 species. They used a statistical model that considered differences in how wind farms searched for dead bats, the size and design of their turbines, and the surrounding environment.

Their results suggest that wind turbines killed an estimated 18.7 million bats between 1981 and 2024. Annual deaths seem to have exceeded 1.5 million from 2021 onwards, which may be the result of more wind turbines being installed.

Hoary bats (Lasiurus cinereus) had the greatest losses, with an estimated 6.7 million deaths, followed by 5.8 million deaths among eastern red bats (Lasiurus borealis), 3.4 million among silver-haired bats (Lasionycteris noctivagans) and 1.5 million among big brown bats (Eptesicus fuscus).

Wind farms near rivers and turbines with longer blades were linked to more deaths among certain species, while having more space between the blades and the ground may reduce the risk.

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The researchers aren’t sure why bats fly so close to wind turbines. Previous work suggests that migratory bats mistake the structures for trees, and approach them in search of food, shelter or mates. A recent European study also found that male bats sometimes sing courtship songs around turbines, potentially attracting females into the path of spinning blades. Differences in species prevalence and behaviours may partly explain why some seem to be more at risk than others.

The researchers hope their findings will help wind farm developers protect bats by choosing safer locations and adjusting turbine designs. Research suggests that stripy wind turbines could prevent seabird collisions, for instance.

Changing when turbines operate might also help. Research shows that temporarily shutting them down during periods of high bat activity, particularly in low winds, can substantially reduce fatalities with limited loss of electricity production.

Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.2612674123