Résumé
Studying fine-scale movements of seabirds during migration is logistically challenging, but GPS technologies allow accurate tracking of individuals on their migratory journeys. Such data provide essential information in the context of offshore wind farm (OWF) developments, notably to anticipate spatial OWF overlap with migratory corridors and main foraging areas used along the routes of vulnerable species. Using high-precision GPS-GSM tags, we investigated the end of summer, southbound migration of two emblematic seabirds of French waters: Juvenile and adult Northern gannets Morus bassanus, and adult Balearic shearwaters Puffinus mauretanicus. Both species travel along the Southwestern European coast, between the Bay of Biscay and Western Africa, or the Mediterranean Sea. Adult gannets thereby migrate through the EEZ of up to 10 countries, six for juvenile gannet, and four for shearwaters. Combining behavioural segmentation based on hidden Markov models and utilization distribution modelling, we found that between two and 6 % of migration routes overlapped with proposed OWFs, with similar impacts on transit and foraging/resting areas. Studied seabirds were most at risk within Portuguese compared to Spanish waters, as they flew closest to OWFs (<10 km on average). While massive OWF developments are being planned within Western European coastal areas, our study suggests that offshore developments should be set >22 km away from the coast, to preserve transnational seabird migratory corridors.
•Northern gannets and Balearic shearwaters rely on coastal areas along Southwestern European coasts during their southbound migration•There is currently limited overlap (2 to 6 %) between seabird migration routes and existing/planned offshore wind farms (OWFs)•Proposed OWFs are not intensively used by individuals during migration (up to 43 % less used than other locations along the sampled migratory route)•To minimize disturbance, OWFs should be constructed farther than 22 km away from Southwestern European coasts.