Winter locations of red‐throated divers from geolocation and feather isotope signatures

• Published in: Ecology and evolution Vol. 12; no. 8; pp. e9209 - n/a
• Main Authors: Duckworth, James, O'Brien, Susan, Petersen, Ib K., Petersen, Aevar, Benediktsson, Guðmundur, Johnson, Logan, Lehikoinen, Petteri, Okill, David, Väisänen, Roni, Williams, Jim, Williams, Stuart, Daunt, Francis, Green, Jonathan A.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-08-2022; John Wiley and Sons Inc; Wiley
• Subjects: Animal feathers; Breeding grounds; Breeding seasons; Ecosystem Ecology; Feathers; Gavia; GLS; Habitats; isotope; Isotopes; loon; Migratory species; Molting; movement; Movement Ecology; Offshore energy sources; Population; Populations; Seasons; Signatures; Software; Wind; Wind farms; Wind power; Winter; Scotland; North Sea; United Kingdom > UK; Europe; Iceland; Finland; loon; Gavia; isotope; movement; GLS
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.9209

Migratory species have geographically separate distributions during their annual cycle, and these areas can vary between populations and individuals. This can lead to differential stress levels being experienced across a species range. Gathering information on the areas used during the annual cycle of red‐throated divers (RTDs; Gavia stellata) has become an increasingly pressing issue, as they are a species of concern when considering the effects of disturbance from offshore wind farms and the associated ship traffic. Here, we use light‐based geolocator tags, deployed during the summer breeding season, to determine the non‐breeding winter location of RTDs from breeding locations in Scotland, Finland, and Iceland. We also use δ15N and δ13C isotope signatures, from feather samples, to link population‐level differences in areas used in the molt period to population‐level differences in isotope signatures. We found from geolocator data that RTDs from the three different breeding locations did not overlap in their winter distributions. Differences in isotope signatures suggested this spatial separation was also evident in the molting period, when geolocation data were unavailable. We also found that of the three populations, RTDs breeding in Iceland moved the shortest distance from their breeding grounds to their wintering grounds. In contrast, RTDs breeding in Finland moved the furthest, with a westward migration from the Baltic into the southern North Sea. Overall, these results suggest that RTDs breeding in Finland are likely to encounter anthropogenic activity during the winter period, where they currently overlap with areas of future planned developments. Icelandic and Scottish birds are less likely to be affected, due to less ship activity and few or no offshore wind farms in their wintering distributions. We also demonstrate that separating the three populations isotopically is possible and suggest further work to allocate breeding individuals to wintering areas based solely on feather samples.
Understanding the distributions of species vulnerable to disturbance from anthropogenic activity is vital in assessing future consequences. Using remote sensing technology, we tracked the movements of red‐throated divers from three breeding locations to identify their overwinter distributions. We then linked these population level differences in distribution to differences in isotopic signatures of feathers grown during the moulting period.