Frequent Use of Offshore Wind Farms in the Southern North Sea by Migrating Terns

Using a high-speed surveillance PTZ camera mounted to a wind turbine in the offshore waters of Belgium, we observed frequent use of the wind farm area by Sandwich Terns Thalasseus sandvicensis and Common/Arctic Terns Sterna hirundo/paradisaea during the spring migration seasons of 2021 and 2022. The terns used a buoy in the wind farm for resting and as a foraging fallback point but were also seen perching on the railing and the platform of the wind turbine itself. In the latter case, terns were foraging close to the base of the turbine. On a few occasions captured sandeel (Ammodytidae) were transported to awaiting females at the turbine. While the potential implications of these behaviours on collision risk remain uncertain, the observed activities underscore the need for comprehensive investigations into the three-dimensional behaviours of terns and other seabirds within offshore wind farm environments.