Abstract
Activity of bats at an old wind park four km off the island of Gotland in the Baltic Sea was monitored during 50 nights from August to October 2013, using an automatic bat detector (Pettersson D500-X) mounted on one of the turbines. Single individuals or pairs of common noctules Nyctalus noctula were recorded on five occasions only (26 and 27 August), all in calm weather and when little or no rotor movement occurred. Since such conditions were unusual (five of 50 nights of observation) the visits by the bats were unlikely to be chance events (migrating bats passing the turbine), but more likely involved bats attracted to the turbines. However, no feeding buzzes were recorded and the bats never stayed near the turbine more than one minute. The turbines studied are lit by 250 W white lights and this could have been the reason why bats visited the turbines, because such lights potentially attract insects. The bats could not have been attracted to the turbines by any factor related of the movement of the rotor or the generator, such as Doppler-effects, noise, heat or electric fields.