Study finds forest bats avoid wind turbines — and noise may be the cause

Bats that forage around forests avoid wind turbines with increasing wind speed when the turbines are in operation, a new study published in the journal Global Ecology and Conservation found.

The study, Forest bat activity declines with increasing wind speed in proximity of operating wind turbines, was carried out by scientists from the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) and the Philipps-Universitat Marburg, Germany. 

The research looked at bats in three foraging groups of species — narrow-space, open-space and edge-space. It studied whether the bats’ activities were influenced by wind turbine operations while both on and off within a radius of 80 to 450 metres under variable wind conditions. 

The researchers observed twelve wind turbine sites in forests of Hesse, Central Germany and found that acoustic activity of narrow-space foraging bats decreased by 77 per cent with increasing wind speed when wind turbines were operating.

When the turbines were turned off, bat activity remained unaffected by wind speed.

Narrow-space foraging bats, which are particularly reliant on forest habitat, showed a significant decrease in activity as wind speed increased in operational wind turbines.

However, the scientists did not observe any significant changes in the activity levels of edge-space and open-space foraging bats in response to the operating mode of wind turbines or wind speed ranging between 0 and 4 metres at 10 metres above the ground.

According to the scientists, one of the causes of this avoidance behaviour is the noise emitted by wind turbine rotors.

The sampling gradient’s starting distance was set at 80m from turbines due to the average size of the cleared area around turbines, which would not be comparable to sites within the forest. The sampling point was set at 450m from turbines due to the small size of forest patches in Germany, which prevents longer distances from being recorded without leaving the forest.

Automated bat recordings took place between May and September 2020 and 2021.

Worldwide, wind turbines are increasingly being built at forest sites to meet the goals of national climate strategies, particularly in Central and Northern Europe. In Germany, about 30,000 onshore wind turbines currently operate at forest sites.

Approximately eight per cent of wind turbines in Germany have already been built in forests, according to a 2023 study. This figure is expected to rise significantly in the coming years as suitable sites in open landscapes become more scarce.

The study design focused on the short-term effects of wind turbine operation on bats. However, long-term effects beyond the timeframe of the study are possible and even likely should the decrease in bat activity close to wind turbines indeed be caused by noise emissions.