When do bird and bat deaths from wind turbines peak? Fatalities studied to reduce harm

New research could help reduce bat and bird fatalities at wind farms in the United States.

According to the analysis published in PLOS One earlier this year, bat fatalities at wind farms peak in certain seasons.The research comes amid growing concern that an increase of wind farms for renewable energy is jeopardizing bird populations.

The analyzed database — developed by the Renewable Energy Wildlife Institute (REWI) to help researchers understand the scope of these fatalities and ripple effects on the larger populations — draws from the American Wind Wildlife Information Center’s post-construction bird and bat fatality data, collected between 2009 – 2021 across 248 operating wind facilities (nearly a third of installed U.S. wind farms). REWI provides “the most detailed, geographically extensive data set of its kind,” according to authors of the study. 

To help reduce fatalities, researchers must first understand why birds and bats collide with turbines in the first place, authors wrote. Previous research has looked into the seasonal patterns in collision fatality rates in a smaller geographical scale.

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“Collision fatalities among birds and bats have been an incidental effect of wind energy since the first large-scale deployments of wind turbines,” authors wrote. “Several decades later, minimizing collision fatalities while maximizing energy production remains a key challenge in efforts to reconcile wildlife conservation with the rapid increase in wind energy that is needed to slow global warming.”

Patterns of bird and bat wind turbine deaths 

The most common bat and bird species to collide with turbines are migratory — meaning they travel long distances seasonally — and fatalities peak during seasonal migration, according to the study. It's difficult to get true estimates of species- or family-specific patterns due to relatively small sample sizes, according to authors. 

• Bird fatalities peak with spring (May) and autumn (September) migration, although fatalities appear to be more common in autumn compared to spring. 
• Like birds, most of the bats killed in collisions with wind turbines undertake seasonal migrations; however, most bat fatalities peak once for a lengthier period of time: from mid- to late summer until early autumn (mid-July to early September) corresponding with migration to wintering areas and mating periods.
• Adjusted fatality rates of bats are highest at wind energy facilities in the upper Midwest and eastern forests.
• Although it is difficult to track specific bat species, some may have differing migratory patterns, meaning fatality rates for specific species could peak later in the year. 

“Apparent differences in timing highlight the need to consider species-specific behaviors as an additional element of (wind turbine) risk,” authors stated. 

More:About 150 eagles killed by wind turbines; company to pay millions after guilty plea

According to a report by the Associated Press published last month and reporting from the Rochester Democrat and Chronicle, part of USA TODAY Network, officials ramped up issuing permits in recent years that will allow wind energy companies to kill thousands of eagles without legal consequence. Data obtained by AP from U.S. Fish and Wildlife Service showed a falloff in enforcement of protection laws for killing or harming protected bald and golden eagles, which began during former President Trump's administration.

The outlet’s findings highlight an ongoing dilemma for officials who must weigh the tradeoffs of clean power development as more birds die from collisions.

“They are rolling over backwards for wind companies,” Mike Lockhart, a former U.S. Fish and Wildlife Service biologist, told the AP. “I think they are killing a hell of a lot more eagles than they ever anticipated.”

According to AP, some wind farm companies have relocated turbines or reduced their numbers to minimize deaths. At the same time, President Biden’s administration has a pending proposal that would further streamline permits that would allow wind-energy projects and power line networks to harm eagles and disturb their nests.