Telemetry reveals strong impacts of offshore wind farms on common guillemots and northern gannets and differing reactions of black-legged kittiwakes during the breeding season

Abstract

**Abstract:** Seabirds have increasingly encountered offshore wind farms (OWFs) in European waters in the past 10 years, resulting in potential conflicts with offshore foraging areas. During the breeding season, seabirds are restricted in their choice of foraging habitats and are under increased pressure to find enough prey to raise their offspring. However, information on the individual reactions of seabirds towards operating OWFs during the breeding season is largely lacking. Three OWFs located 23-35 km north of the island of Helgoland in the southern North Sea are operating since 2015. We studied their effects on locally breeding northern gannets, black-legged kittiwakes and common guillemots using GPS tracking between 2015 and 2017. GPS tags were deployed on 63 breeding individuals for 0.1-13.9 weeks. Most gannets and guillemots predominantly avoided OWFs. A point process modelling approach revealed a significantly reduced resource selection inside the OWFs compared to the surroundings for both species. OWF avoidance by guillemots was even stronger when turbine blades were rotating. Only few gannets frequently entered OWFs when foraging or commuting. Flight altitudes of gannets inside the OWFs were close to the rotor-blade zone, especially for individuals predominantly avoiding the OWFs and during commuting. Kittiwakes mainly avoided OWFs close to the colony but sometimes entered OWFs which were located in further distance to the colony. These results provide a detailed description of seabirds' reactions to OWFs during the breeding season, and one of the first comprehensive analyses of OWF effects on these species based on telemetry data. The documented effects need to be considered during the planning processes for future OWFs, especially for locations close to large seabird breeding colonies. **Authors:** Verena Peschko¹, Nele Markones¹, Bettina Mendel¹, Moritz Mercker², Stefan Garthe¹ ¹University of Kiel, ²BIONUM