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ISU-based study determines cause of bat deaths at wind farms

A research team based at ISU has conducted a study to determine the cause of thousands of bat deaths every year at wind farms.

The study determined traumatic injury from collision with the turning blades to be the most likely cause of recent bat deaths. This conclusion contradicts the widely accepted theory that bats die from barotrauma: ruptured lungs from entering the low pressure area caused by the wind blades.

Katie Rollins, ISU master of biological science graduate, was a lead researcher on the study that tested the collision versus barotrauma theories.

“We determined that decomposition of lung tissue in the hours after death, as well as changes caused by blunt trauma, can commonly cause tissue damage that mimics barotrauma,” Rollins said.

“Therefore, using lung tissue to diagnose the cause of bat mortality at wind farms can lead to an overestimation of barotrauma,” she added.

Rollins and her team examined bats found dead at a Central Illinois wind farm for signs of collision with the wind blades. They also looked for evidence of barotrauma by examining the bat’s ear drums for rupture.

“We conducted experiments with mouse lungs to determine the effects of decomposition and temperature on lung tissue,” Rollins said.

“This mimics what happens when a dead bat is lying on the ground at a wind farm before being found and picked up by a researcher,” she added.

Angelo Capparella, School of Biological Sciences associate professor and co-researcher of the study, explained the importance of bats as a natural pest control agent and their role in the ecosystem and food web.

“As a group, bats are being inflicted with harm by all sorts of human activities,” Capparella said.

“This group of animals is of great concern to conservationists interested in preserving biodiversity,” he added.

With the major cause of bat fatalities being identified, conservationists are able to refocus on developing appropriate strategies to reduce bat deaths.

Currently, the most effective mitigation strategy is curtailment: increasing the wind speed required for turbines to begin spinning.

“The majority of bats die on low wind speed nights, so curtailment leaves turbines non-operational on nights when bats are most likely to be migrating,” Rollins said.

However, even with curtailment, a large number of bats will still be killed on wind farms.

Rollins said continued research into effective mitigation strategies is necessary to further reduce the number of bats being killed.