Offshore wind farm avoidance by a discard-feeding seabird is independent of local fishing activity.

Offshore wind farms are increasing rapidly in number and scale, presenting potential risks for seabirds. Some seabirds actively avoid offshore wind farms, whereas others are attracted to them. Both avoidance and attraction can have detrimental effects, including habitat loss and increased collision mortality. Because commercial fishing is typically restricted within wind farm boundaries, apparent avoidance by discard-feeding species may reflect attraction to nearby fishing activities rather than actual wind farm avoidance Here we studied the temporal variation in avoidance and attraction of 58 GPS-tracked Lesser Black-backed Gulls (Larus fuscus) to both the offshore wind farm and fishing activity within the foraging range from their breeding colony. If apparent avoidance of offshore wind farms was caused by an attraction to nearby fisheries, we expected a lower selection strength of the offshore wind farm during weekdays when fishing activity is much higher compared to weekends. We used a step selection analysis to estimate relative selection strength including individual variability and tested if the selection strength for wind farms and fishing activity differed between the pre-breeding, breeding and post-breeding periods, between sexes, and between weekdays and weekends. At the population level, gulls avoided the offshore wind farm during most periods and selected areas with fishing activity compared to areas without. The selection strength of wind farms and attraction to fisheries varied substantially between individuals, with several males being attracted to the wind farm during the breeding and post-breeding period. Variation between individuals in avoidance of offshore wind farms varied most during the breeding period. The attraction to fishing activity did not differ between periods and sex. Fishing intensity was four times lower during the weekends than during weekdays. However, we found no support that gulls differed in wind farm avoidance between weekdays and weekends, suggesting that avoidance is not primarily driven by fishing exclusion within wind farms. This research contributes valuable empirical data to improve the biological realism of Collision Risk Models by demonstrating that individual variability in avoidance behaviour warrants the inclusion of behavioural heterogeneity in these models rather than assuming uniform population responses.