The primary focus of the Wozep research is on acquiring more knowledge about the specific conditions in which, and why, bats fly out to sea and about how bats behave in offshore wind farms (do they fly past and/or over them, do they stay near turbines, do turbines specifically attract bats etc.).  In order to see how bats move along the coast and over the sea, Wozep is conducting studies with telemetry stations and tagged Nathusius's pipistrelles. The tags broadcast a radio signal which is picked up by the stations. In addition, there is research using acoustic observations (bat detectors), which record the echo signal that bats use to determine their position and find food.

There are many different species of bats in the Netherlands. A number of these species are also found flying over the North Sea, including Nathusius's Pipistrelle (Pipistrellus nathusii) and the Common Noctule (Nyctalus noctula). They cross the North Sea at various places during the annual migration to and from the UK. Bats sometimes also look for food (swarms of insects) over the North Sea. Research has shown that bats may, depending on the season, temperature, wind strength and wind direction, fly over and across the North Sea to a greater or lesser extent.

Bats use echolocation to find food (insects) and avoid obstacles. It is possible that bats may be poor at detecting rapidly moving objects, such as the blades of a rotating wind turbine, which therefore pose a potential danger. However, the highest risk is associated with the pressure wave caused by the rotating rotor blades. Bats that fly near this pressure wave may suffer a rapid drop in air pressure that inflicts barotrauma and therefore damage to organs that can often result in death.

Bats are a protected species group and so Wozep (the Offshore Wind Ecological Programme) is conducting research to determine the possible effects of the presence of offshore wind farms. This information can be used to draw up specific bat regulations in order to reduce bat casualties.

Use of the study results

The bat research helps to reduce uncertainties relating to the impact of offshore wind farms on bats. This will result in more accurate environmental impact assessments for the wind farms in the future. In addition, it will allow for more accurate calculations with the  Framework for Assessing Ecological and Cumulative Effects (KEC) (KEC) of the cumulative effects of wind farms on bats. The KEC quantitatively assesses the potential cumulative ecological effects of the wind farms in the southern North Sea at present, as well as of wind farms that are under construction or planned for the future. In addition, a better understanding of the effects will provide a firmer footing for permit requirements that will be included in the site decisions for the wind farms.  In 2019, new Wozep research data and analyses resulted in a clearer picture of the conditions that determine the timing of bat migration. This led to the first refinement of the requirements relating to bats in the site decisions for the offshore wind farms that will go into operation from 2020 onwards. Bat migration peaks at night between 25 August and 10 October. The regulations require wind turbines to be virtually shut down during this period in specific weather conditions (the blades must not rotate faster than two revolutions a minute). The aim is to strike the optimal balance between preventing bat collisions and limiting the loss of energy production. It appears that this measure will keep the risk of casualties within acceptable limits.

Ongoing Wozep research

In 2020, there will be bat detectors at fourteen different locations on the North Sea. It is hoped they will help to enhance the robustness of the existing dataset and plot possible migration routes. In addition to the bat detectors, the research also involves monitoring radio signals from tags attached to the bats. In 2018 and 2019, a total amount of approximately 300 individual bats were tagged. They are tracked with a network of stationary receivers (telemetry stations) mounted on lighthouses and blocks of flats along the coast. The data are used to determine the routes and directions taken by the individual bats. The extension of this network to offshore wind farms could provide more data about how bats behave in the vicinity of a wind turbine. In that way, we hope to establish a clearer picture of the extent to which offshore wind farms affect bats.

List with reports on completed studies

IDON Newsletter item (in Dutch)