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Study: Wind turbine collisions causing bat deaths, not low pressure field

Wind farms are associated with high numbers of deaths among migrating bats, with annual mortality estimates ranging as high as tens of thousands of bat deaths at some wind farms.

A research team based at Illinois State University, which included University of Iowa scientist David Meyerholz, D.V.M., Ph.D., used forensic pathology to determine the cause of bat deaths at wind farms.

The study, published in the March issue of the journal Veterinary Pathology, concludes that traumatic injury from collision with turning turbine blades is the most likely cause of bat deaths. That finding contradicts a widely reported explanation that bats die from barotrauma, essentially ruptured and bleeding lungs caused by entering a low-pressure field created by the turning blades.

“Our study suggests that pulmonary barotrauma is a misdiagnosis of the evidence from the lungs of the dead bats,” says Meyerholz, a UI associate professor of pathology and comparative lung pathologist, who was co-lead author of the study.

Bats are an integral part of food webs and play a critical role in pest control that’s worth at least $3 billion per year to America’s crop farmers. Understanding the causes of bat fatalities at wind farms is important for scientists and policy makers looking for ways to mitigate or prevent the loss of these important animals.

Meyerholz and colleagues conducted experiments with mouse lungs and showed that decomposition of tissues in the hours after death, as well as changes caused by blunt trauma, can commonly cause tissue damage that mimics barotrauma.

The team also obtained specimens of bats that had flown into high-rise buildings from the Field Museum of Natural History in Chicago. By examining these specimens they were able to determine the extent of traumatic injuries for collision with static objects. Comparison of these specimens with bat specimens from a central Illinois wind farm showed that the presence of turning turbine blades was associated with significantly more frequent and more severe traumatic injuries in the bats.

“This study raises some serious questions about the foundation of barotrauma theory in wind farm bats and simultaneously demonstrates by multiple lines of evidence that the collision theory is the basis for most of these deaths,” Meyerholz says. “Clarifying the cause of bat deaths focuses future studies on understanding why migrating bats are prone to these collisions and will guide development of appropriate mitigation systems to reduce these deaths.”