In recent years nature conservation organizations and authorities in Germany became increasingly aware of bat fatalies at wind turbines and the legal implications of this. This led to the introduction of mitigation measurements in order to prevent bat fatalies as much as possible.In wind parks with high bat activity the only mitigation measures available are often site choice for individual turbines and switching off the turnbines during critical periods. Additionally there is often an obligation to carry out bat monitoring after the turbines have been constructed to adjust the mitigation measurements, especially to define cut-in wind speed, and to identify seasonal patterns with high bat activity. In this poster we present two of our monitoring studies, one at the coast and the other 200 km inland. We will concentrate on the influence of wind speed on bat activity.