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

doi:10.3354/meps14533

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MEPS 730:113-129 (2024) - DOI: https://doi.org/10.3354/meps14533

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

Nina J. O’Hanlon^1,*^,^#, Rob S. A. van Bemmelen^2,10^,^#, Katherine R. S. Snell³, Greg J. Conway⁴, Chris B. Thaxter⁴, Helen Aiton⁵, David Aiton⁵, Dawn E. Balmer⁴, Sveinn Are Hanssen⁶, John R. Calladine¹, Sjúrður Hammer^7,11, Sarah J. Harris⁴, Børge Moe⁸, Hans Schekkerman⁹, Ingrid Tulp², Elizabeth M. Humphreys¹

¹British Trust for Ornithology Scotland, Beta Centre (Unit 15), Stirling University Innovation Park, Stirling FK9 4NF, UK
²Wageningen Marine Research, Haringkade 1, 1976 CP IJmuiden, the Netherlands
³Max Planck Institute of Animal Behavior, Am Obstberg 1, 78315 Radolfzell, Germany
⁴British Trust for Ornithology, The Nunnery, Thetford, Norfolk IP24 2PU, UK
⁵Cuppar, Evie, Orkney, UK
⁶Norwegian Institute for Nature Research, Sognsveien 68, 0855 Oslo, Norway
⁷Faculty of Science and Technology, University of the Faroe Islands, Vestarabryggja 15, 100 Tórshavn, Faroe Islands
⁸Norwegian Institute for Nature Research, PO Box 5685 Torgarden, 7485 Trondheim, Norway
⁹SOVON, Toernooiveld 1, 6525 ED Nijmegen, the Netherlands
¹⁰Present address: Waardenburg Ecology, Varkensmarkt 9, 4101 CK Culemborg, the Netherlands
¹¹Present address: Faroese Environment Agency, Traðagøta 38, 165 Argir, Faroe Islands

*Corresponding author: nina.ohanlon@bto.org
^#These authors share equal authorship

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, the 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 (r_M = 0.25, 95% CI = 0.09-0.42; 0 = weak connectivity, 1 = strong connectivity) and northbound (r_M = 0.16, 95% CI = -0.02 to 0.33) migration. Variation in migration strategies was driven by individuals from Svalbard, which belong to a population that is declining less than the other populations tracked. The 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 towards linking conditions during migration to population dynamics and prioritising future research and conservation actions.

KEY WORDS: Arctic skua · Stercorarius parasiticus · Staging areas · Migration strategies · Conservation · Geolocators · Saltwater immersion data

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Cite this article as: O’Hanlon NJ, van Bemmelen RSA, Snell KRS, Conway GJ and others (2024) Atlantic populations of a declining oceanic seabird have complex migrations and weak migratory connectivity to staging areas. Mar Ecol Prog Ser 730:113-129. https://doi.org/10.3354/meps14533

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