Acoustic bat activty at wind turbines in temperate forests - Avoidance patterns and potential causes

Anthropogenic activities have caused two current major crises: biodiversity decline and climate change. Climate change mitigation is largely accepted as a societal goal and policy makers unite forces to substantially reduce carbon dioxide emission. However, the ongoing transition from fossil to rene...

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Bibliographic Details
Main Author: Ellerbrok, Julia Sophie
Contributors: Farwig, Nina (Prof. Dr.) (Thesis advisor)
Format: Doctoral Thesis
Language:English
Published: Philipps-Universität Marburg 2023
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Summary:Anthropogenic activities have caused two current major crises: biodiversity decline and climate change. Climate change mitigation is largely accepted as a societal goal and policy makers unite forces to substantially reduce carbon dioxide emission. However, the ongoing transition from fossil to renewable energy sources, such as wind energy, is not without impact on biodiversity, thereby creating a conflict of two sustainability objectives. Wind turbines are increasingly built in forest ecosystems, which present important foraging and roosting habitats for European bats. Forest bats may be affected by the deployment of wind turbines through collisions with the rotor blades, through habitat losses where forest is cleared, and through displacement effects. In this thesis, I investigated effects of wind turbines in forests as reflected in activity patterns of local bat communities. To this end, I performed an acoustic study across 22 wind turbines sites in temperate forests of Hesse, Central Germany. I determined bat activity levels at wind turbine clearings, at adjacent forest edges and in the surrounding forests at distances between 80 m and 450 m to the closest wind turbine. Recorded bat activity was investigated for three foraging guilds: narrow-space foraging bats specialized on flight in vegetation clutter, edge-space foraging bats specialized on flight in semi-open habitats like forest edges, and open-space foraging bats specialized on flight above forest canopies. I found that bats were negatively affected by wind turbines in forests. Specifically, narrow-space foraging bats avoided wind turbines over distances of at least 450 m, which presents an indirect habitat loss for these bats. The avoidance was at least partly explained by noise emissions of operating wind turbines which were amplified by high wind speeds. In contrast, the presence of cleared spaces around wind turbines did not contribute to the avoidance in narrow-space foraging bats. Edge-space and open-space foraging bats were less susceptible to displacements by wind turbines. Instead, they displayed higher activity levels at wind turbine clearings than in the surrounding forest canopies which might lead to increased collision rates for these bats in comparison to wind turbines in open landscapes. This thesis highlights the existence of forest-specific wind turbine effects on bat activity patterns which may affect local bat communities and populations. Consequently, when wind turbines are installed and operated in forests, forest-specific conservation measures are required, e.g., the exclusion or compensation of forest areas with heterogeneous vegetation structure and the reduction of turbine noise emissions. Such measures will contribute towards resolving the bat-wind energy conflict as an example of how objectives of climate change mitigation and biodiversity conservation can be reconciled.
DOI:10.17192/z2023.0535