Six pelagic seabird species of the North Atlantic engage in a fly-and-forage strategy during their migratory movements
Résumé
Bird migration is commonly defined as a seasonal movement between breeding and non-breeding grounds. It generally involves relatively straight and directed large-scale movements, with a latitudinal change, and specific daily activity patterns comprising less or no foraging and more traveling time. Our main objective was to describe how this general definition applies to seabirds. We investigated migration characteristics of six pelagic seabird species (northern fulmar, common guillemot, Brünnich’s guillemot, little auk, Atlantic puffin, black-legged kittiwake). We used an extensive geolocator positional and activity dataset from 29 colonies in the North-East Atlantic and across several years (2008-2019). We used a novel method to identify active migration periods based on segmentation of time series of track characteristics (latitude, longitude, net-squared displacement). Additionally, we used the wet/dry data of geolocators to infer bird activity. We found that the six species had, on average, three to four migration periods and two to three distinct stationary areas during the non-breeding season. On average, seabirds spent the winter at lower latitudes than their breeding colonies and followed specific migration routes rather than non-directionally dispersing from their colonies. Differences in daily activity patterns were small between migratory and stationary periods, suggesting that all species continued to forage and rest while migrating, engaging in a “fly-and-forage” migratory strategy. We thereby demonstrate the importance of habitats visited during seabird migrations as those that are not just flown over, but which may be important for re-fuelling.