The species identified are the Nathusius’ pipistrelle (Pipistrellus nathusii) (see photo, © René Janssen) and the common noctule (Nyctalus noctula). Both species are known to cover long distances during migration, so these observations could refer to migrants . However, they could also be local populations flying back and forth from the mainland to forage. There are no indications of the presence of bat roosts in the wind farms. A follow-up study has already been started to gather information on how these bats are using the offshore wind farms.

The pilot study was carried out in autumn 2012 by the Fieldwork Company and IMARES Wageningen UR, in association with both wind farms. The study was prompted by Swedish research confirming the presence of bats in an offshore wind farm in the Baltic Sea. In addition, the presence of bats had already been noted on the Dutch Continental Shelf: on drilling rigs and ships, and observers regularly see them flying from the sea into coastal locations.

Ultrasonic sound recorders

Between late August and October 2012 ultrasonic sound recorders were used to prove that bats are present in Dutch offshore wind farms. These recorders register the sonar that bats use to navigate and forage during flight. Most species transmit a species- specific signal.

The equipment confirmed the presence of bats in both offshore wind farms. A total of 189 call sequences was recorded in Offshore Wind Farm Egmond aan Zee (29 Aug-20 Oct) and 25 in Princess Amalia Wind Farm (4-23 Sept). Of these sequences, 98% consisted Nathusius’ pipistrelle species and 2% common noctule. Most of the bat activity occurred early September.

Future research

This study shows that bats occur in Dutch offshore wind farms. Very little is known about their migration routes across the North Sea or their use of offshore wind farms as foraging area. As bats are a protected species, further research is necessary in order to account for the presence of bats at sea in the future. A follow-up study is the first step.