The objective of this study is an investigation of potential conflicts between windmills and birds. Emphasis is on frightening, collision risk and biotopic changes due to windmill systems. The study is based on the environment of Koldby and Nibe windmills (South Jutland). Biotopic changes were not observed around the existing windmills. Drainage of mill grounds at Nibe had probably no effect on water level in the area around; a longer observation is necessary to draw any decisive conclusions.(EG).