Impacts of offshore wind farms on migratory bats in British waters

Offshore wind energy projects are developing at pace with ambitious Net Zero targets in place across Europe and understanding the evidence base for the environmental effects of offshore wind development and operation is essential. The evidence for bats moving across seas surrounding the UK is growing, making it critical to better understand the impact of offshore wind energy on bats. We review the literature examining bat migration within and between the British Isles and Europe as well as the interaction of bats with wind energy infrastructure. Based on data available, Nathusius' pipistrelle (Pipistrellus nathusii) are the most commonly recorded species offshore and are considered a regular migrant to the British Isles therefore putting them at the highest risk for interactions with offshore wind turbines. We also review evidence to suggest that long distance migratory Nyctalus spp. may migrate between the British Isles and Europe or Scandinavia as well as highlighting potential impacts of non-migratory activity offshore. We find that whilst it is widely assumed that bat behaviour around offshore wind turbines is likely to be similar to onshore, there is currently a lack of studies specifically reporting how bats interact with offshore wind turbines. A number of hypotheses have been proposed to explain why bats are killed by wind turbines and a likely negative consequence of wind turbine-related mortality is the cumulative impact on bat populations across Europe, particularly for migratory species. To close key gaps in the evidence, future studies should focus on migration routes, phenology and behaviour of bat species crossing open sea including future wind energy development scenarios. It is also important that future work aims to establish the specific impact on bat species in the offshore environment including; if bats are killed at offshore wind turbines, the number of casualties and what conditions influence collisions.