Wind turbines are displacing bats from their forest habitats

Wind turbines, a growing source of renewable energy, have been found to significantly impact bat populations, not only causing fatalities but also displacing them from their natural habitats. 

A recent study led by the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) and Philipps-Universität Marburg reveals a startling decrease in bat activity near these turbines. 

Avoidance behavior 

The study indicates an almost 80 percent drop in the activity of bats that hunt in dense habitats like forests, within a radius of 80 to 450 meters around operational turbines during high wind speeds. The researchers suggest that the noise emitted by the turbine rotors, escalating with wind speed, is likely causing this avoidance behavior.

Wind energy expansion 

As the world shifts towards renewable energy to meet climate goals, more wind turbines are being installed. Germany, for example, operates around 30,000 onshore wind turbines. 

The search for new turbine sites has extended to forests, which are vital habitats for many European bat species, such as the greater mouse-eared bat (Myotis myotis). The expansion of wind energy in these forested areas poses not only a direct collision risk with turbine rotors but also indirect negative impacts on bat species. 

The study, led by Christian Voigt from Leibniz-IZW and Nina Farwig from Philipps-Universität Marburg, highlights the considerable avoidance distance of forest-dwelling bats from operational turbines.

Key findings

Julia Ellerbrok, a postdoctoral research fellow in the Department of Biology at Philipps-Universität Marburg and a former doctoral student in the project, explained the findings. 

Operational factors 

“We investigated the activity of different bat species in different wind conditions and during the operation of wind turbines in forests in the German federal state of Hessen,” said Ellerbrok.

“We found that the activity of bats, which usually forage in narrow, structurally dense vegetation of forests, decreases by 77 percent on average within a radius of 80 to 450 meters around the wind turbines with increasing wind speed when the turbines are in operation. In contrast, bat activity was unaffected by wind speed when the turbines were switched off.” 

This led the team to conclude that the operational factors of the turbines at high wind speeds are causing such avoidance behavior.

Noise emissions

“The rotor movements of wind turbines not only generate so-called wake turbulences but also substantial noise,” added Christian Voigt, head of the Department of Evolutionary Ecology at the Leibniz-IZW. 

“Both factors can affect bats over several hundred meters. Forest bats that hunt under the canopy presumably do not come into contact with the wake vortices. Rather, they could be affected by the noise emissions of the turbines, even if the frequency range of the noise is far below those of the echolocation calls. If bats actively avoid noise emissions from wind turbines, they lose valuable habitat on a large scale.”

Broader implications 

The research team concludes that wind turbines in forests present multiple challenges for bats. Not only is valuable habitat lost both during construction and operation of these turbines, but bats hunting above the treetops are also at risk of collision with the rotating blades. 

To minimize the long-term ecological impact on bat populations in forested areas, the researchers suggest that wind turbines should be erected only in structurally poor forest plantations with fewer bats. They also emphasize the need for future research to further investigate the effects of noise emissions from turbines on bats.

The research is published in the journal Global Ecology and Conservation.

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