Until now, there has been no technical basis for a threshold that could serve as the foundation for nationwide uniform rules on turbine shutdowns to protect bats. Guidance documents and practical handbooks in the federal states currently work with a range of thresholds for the maximum number of bats killed by wind turbines, ranging from fewer than 0.5, to fewer than 1, up to 2 dead animals per turbine per year.
The so-called significance threshold defines how many dead bats per wind turbine per year can be tolerated. For this reason, the Federal Agency for Nature Conservation commissioned a corresponding research and development project in 2021. The BfN has now presented the results.
As part of the project, a draft methodology for deriving the significance threshold was developed on the basis of specialist literature, administrative provisions and court rulings. It proposes a nationwide uniform threshold of, on average, fewer than one animal per turbine per year. In the view of the experts, this is the only way to prevent possible negative impacts on the sensitive populations of some bat species. Since bats have a very low reproductive rate, even slightly increased mortality rates can lead to a heightened risk of extinction.
The publication of the recommendation by the Federal Agency for Nature Conservation is intended as a contribution to the discussion on standardisation. Its aim is to support the expansion of wind energy in a way that is as compatible with nature conservation as possible, while minimising potential adverse effects.
In addition, the publication contains shutdown requirements differentiated by region and season, making it possible in future to tailor turbine shutdowns for bat protection more precisely and reduce them to the necessary minimum.
In order to incorporate the expertise of various stakeholder groups into the recommendation, an initial draft of the technical recommendation was sent to a range of stakeholders for comment, including the German Wind Energy Association (BWE). After submitting its comments, the BWE withdrew from the consultation process.
Technical recommendation for a nationwide significance threshold for bats – assessment of the current significance threshold for bats and wind turbines. Markus Dietz, Anja Fritzsche, Adrian Johst, Nina Ruhl. BfN-Schriften 764, Bonn, 2026. (The English translation is available since April 2026)