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MEPS prepress abstract   -  DOI:

Atlantic populations of a declining oceanic seabird have complex migrations and weak migratory connectivity to staging areas

Nina J. O’Hanlon*, Rob S. A. van Bemmelen, Katherine R. S. Snell, Greg J. Conway, Chris B. Thaxter, Helen Aiton, David Aiton, Dawn E. Balmer, Sveinn Are Hanssen, John R. Calladine, Sjúrður Hammer, Sarah J. Harris, Børge Moe, Hans Schekkerman, Ingrid Tulp, Elizabeth M. Humphreys

*Corresponding author:

ABSTRACT: Anthropogenic change is impacting ecosystems globally, causing declines in biodiversity. Long-distance migrants are particularly susceptible as they depend on conditions over large geographical scales and are likely to experience a greater range of pressures. One long-distance migrant that has experienced substantial declines across the North-East Atlantic is the Arctic Skua Stercorarius parasiticus. However, little is known about their migratory routes or strategies. We tracked 131 Arctic Skuas from Scotland, Faroe Islands, Norway and Svalbard between 2009 and 2019 using geolocators. To investigate migration strategies, we applied a Hidden Markov Model, using saltwater immersion data, to infer stopovers and transit flights. Skuas used several discrete staging areas during migration with an area of high marine productivity in the mid-North Atlantic being of high importance. Individuals from the different breeding populations overlapped extensively in staging areas, resulting in weak spatial connectivity between breeding and staging areas during southbound (RMantel = 0.25, 95% CI: 0.09 - 0.42; 0 = weak connectivity, 1 = strong connectivity) and northbound (RMantel = 0.16, -0.02 - 0.33) migration. At the population-level, variation in migration strategies was driven by individuals from Svalbard, which is declining less than the other populations tracked. Relative location of wintering areas also influenced migration strategies. Individuals migrating further spent a smaller proportion of their migration at stopovers than those wintering closer. Identifying the non-breeding distribution, migration strategies and weak migratory connectivity of Arctic Skuas provides a vital step to link conditions during migration to population dynamics and prioritise future research and conservation actions.