Abstract
Small wind turbines (SWTs) have become increasingly common in several European countries, but knowledge of their impact on wildlife, especially bats, remains relatively scarce. We applied an operational experiment at 10 SWTs in Northern Germany to determine the bat species commonly found at those SWT sites and whether the operational state of the SWT affects bat activity or behavior. During the experiment, the SWT operational state (“ON”, “OFF”) was altered and the flight trajectories of bats around the SWTs were documented using a specifically designed 3D camera with a high spatial resolution able to capture collisions with the structures. Several bat species were detected in the close vicinity (20 m) of the SWTs at all study sites. The bat species group “Nyctaloids” dominated bat acoustic activity at most SWTs, followed by Pipistrellus pipistrellus and P. nathusii. Only 41 of the 499 flight trajectories approached the nacelle closer than 10 m, including one that passed the rotor blades directly. Generally, there was no evidence of collisions nor was there an influence of operation mode on either bat acoustic activity levels or the distance of bat flight trajectories to the nacelle. However, we strongly caution that the results of our study cannot be generalized to other landscapes, weather conditions, bat species, or SWT types.