In Germany in recent years, an increasing number of wind turbines are being planned in forests. The bat surveys for impact assessments are carried out on the forest floor using line transects. This method does not take into consideration that bat activity above and below the canopy might differ. So far, few studies have investigated bat activity above the forest canopy in Germany (Aschoff et al. 2006, Fichtner 2004), or elsewhere (Grindal & Brigham 1999, Hayes & Gruver 2000, Kalcounis et al. 1999). The aim of our study was to test the following hypotheses: bat activity and species composition above and below the canopy differs wind strongly influences bat activity above the canopy, but less so below the canopy assessing bat activity and species composition above the canopy from surveys at ground level is difficult or even impossible.