How do gulls interact with offshore wind farms? Assessing avoidance and behaviour of lesser black-backed gulls using GPS telemetry and accelerometry

Abstract

**Abstract:** Renewable energy deployments, including wind farms, are a key part of government strategies to mitigate the impacts of anthropogenic climate change. Wind farms, however, pose a potential collision risk to air-borne taxa, that may be influenced by the individual behaviour of species, flight altitude, speed and exposure time. Nevertheless, we have limited understanding of how species behave within wind farms, and lack empirical evidence for avoidance/attraction responses at different spatial scales. We used GPS telemetry and accelerometry to examine how adult Lesser Black-backed Gulls Larus fuscus breeding at South Walney (Cumbria, UK) used offshore wind farms during the breeding season. The variation in spatial and temporal use of wind farms was first assessed across the years of study (2014-2019), within the breeding season (ca. March-August) and by time of day. We then used a range of classification methods to determine behaviour of birds, including Hidden Markov Models, Expectation-Maximization Binary Clustering, and accelerometry. Methods were also compared for their congruence in behavioural classification. A randomisation approach was used to investigate 3D avoidance and attraction to wind turbines at two different spatial scales: macro (wide-scale) avoidance of wind farms and meso (near-scale) avoidance of turbines. Birds frequently commuted through wind farms to reach foraging locations. However, many slower sinuous movements and 'stopped' behaviours were recorded around turbines and other associated platforms. Macro-avoidance was evident outside the wind farm, but varied spatially and weakened nearer to wind farms. Within wind farms, birds avoided the 3D rotor sweep volume of individual turbines, driven by a meso-avoidance response within and above the vertical rotor-sweep zone, but below this zone, birds exhibited attraction to turbine bases or platforms. These findings are providing robust site-specific collision estimates, in turn reducing uncertainty within impact assessments, and informing the conservation of a species that has experienced notable declines in coastal populations in recent years. **Authors:** Chris Thaxter¹, Daniel Johnston¹, Willem Bouten², Gary Clewley¹, Viola Ross-Smith¹, Nigel Clark¹, Elizabeth Masden³, Emily Scragg¹, Elizabeth Humphreys¹, Greg Conway¹, Lee Barber¹, Ros Green¹, Aonghais Cook¹, Niall Burton¹ ¹British Trust for Ornithology, ²University of Amsterdam, ³Environmental Research Institute