New insights into the influence of turbines on the behaviour of migrant birds: implications for predicting impacts of offshore wind developments on wildlife

Knowledge of the movement and behaviour of birds and bats around turbines in the offshore marine environment is critical for assessing the environmental impacts of offshore wind developments in the eastern USA. To address the problem of gathering high-quality, long-term data on these species in this remote environment, we designed a multi-sensor system that was recently deployed for 6 months in 2021 and 2022. Two Acoustic and Thermographic Offshore Monitoring (ATOM™) systems were deployed on wind turbines 23 nautical miles off the coast of Virginia, USA. The systems were operational during the day and night and recorded 1,581 detections of birds and bats, with 99% of detections occurring in the fall. Most detections were of birds, including 5 shorebird species, 3 gull species, 1 tern species, 3 raptor species, 1 woodpecker species, and 18 passerine species. Skuas, corvids, and swallows were also observed. There were 521 detections of bats. Differences between species detected and identified in each sensor confirms that a multi-sensor approach for monitoring is beneficial. There were no observed collisions; two individuals (1 bird and 1 bat) suffered air displacement, causing them to fall, but they recovered and continued flying. ATOM also collected novel data on insects, tracking over 7,000 insects around the turbine rotor swept zone and revealed foraging behaviour in 596 of the 1,581 bird and bat detections. Offshore wind turbines thus provide potential sites for perching and foraging. Although these turbine sites provide a new opportunity to feed, which may be beneficial for insectivores and omnivores in enabling them to reach migration destinations in better condition, the consequences of a potentially delayed arrival are unknown (positive, negative, or neutral). Overall, our approach produced the first detailed insights into terrestrial land bird and bat activity around offshore turbines, providing novel information on changes in behaviour when turbine blades are moving and during higher wind speeds. Moreover, our data show that foraging activity appears to be conducted with an awareness of the moving blades and in safe zones close but parallel to blade movements. We recorded 113 observations of activity within 10 m of the moving blades and 70 observations where interactions with moving turbine blades were within 1 m; we call these latter avoidance measures nanoavoidance. No collisions were observed.