Diel movements and flight altitudes of the European storm-petrel in the North Atlantic and their implications for conservation

Understanding the movement patterns and foraging areas of seabirds is critical for their conservation and for mitigating potential impacts from human activities, such as offshore wind farm (OWF) development. We provide the first GPS data on foraging trips and travel altitudes of European storm-petrels (ESP) Hydrobates pelagicus in the Bay of Biscay, near planned OWF development areas. We obtained 28 complete trips from 19 individuals during the incubation periods of the 2023 and 2024 breeding seasons at three colonies along the Spanish Cantabrian shore. Distribution models for ESP were developed using the maximum entropy (MaxEnt) method for each colony, and flight heights were measured using GPS triangulation, analysing data separately for daytime and nighttime. Mean trip duration was 2.7 days and mean trip distance travelled was 803 km, with no relevant differences among colonies. Our results indicate that foraging areas were concentrated along the edges of both the French and Iberian continental shelves. However, at night, ESP showed a more concentrated use of the continental shelf edge and exhibited a more coastal distribution, occasionally foraging in bays and estuaries and showing inter-colonies nocturnal movements. This nocturnal scenario may pose a risk of direct impact of OWFs on the breeding population of the species in the Gulf of Biscay.