Atlantic populations of a declining oceanic seabird have complex migrations and weak migratory connectivity to staging areas
Author(s): O'Hanlon, N.J., van Bemmelen, R.S.A., Snell, K.R.S., Conway, G.J, Thaxter, C.B., Aiton, H., Aiton, D., Balmer, D.E., Are Hanssen, S., Calladine, J.R., Hammer, S., Harris, S.J., Moe, B., Schekkerman, H., Tulp, I. & Humphreys, E.M.
Published: March 2024
Journal: Marine Ecology Progress Series Volume: 730
Digital Identifier No. (DOI): 10.3354/meps14533
Tracking the long-distance migrations of Arctic Skuas from their north-east Atlantic breeding grounds revealed complex migration strategies, with mixing of individuals from different populations at important staging areas before the birds reached their southern wintering grounds.
Arctic Skuas are long-distance migrant seabirds that have seen large declines in breeding numbers across areas of the north-east Atlantic. Part of these declines has been attributed to poor food availability during the breeding season, exacerbated by predation from Great Skuas, particularly in years where food availability is low. However, Arctic Skuas only spend around a third of the year at their breeding grounds. Therefore, they likely also face a range of threats during the non-breeding season.
To shed light on the migration routes and strategies of Arctic Skuas, researchers, including BTO scientists, tracked 131 individuals with small tracking devices called geolocators between 2009 and 2019, collecting information from four breeding populations: Scotland, the Faroe Islands, Norway and Svalbard. This collaboration revealed extensive mixing of Arctic Skuas from different breeding populations during migration in several discrete staging areas. An area of high marine productivity, part of which has recently been designated as a high seas Marine Protected Area, was particularly important to the skuas during both their south-bound (autumn) and north-bound (spring) migrations. Because of their predictable food sources, such staging areas are vital, fuelling long flights to the wintering areas and, during spring, enabling individuals to build up reserves for the upcoming breeding season.
This considerable mixing of individuals means that if adverse conditions affect the skuas in these important staging areas, then it has the potential to negatively impact multiple breeding populations through reduced survival or productivity.
However, the data also revealed some differences in the migration routes and staging areas of individuals from the different breeding populations. Specifically, during southbound migration, skuas from Scotland largely migrated south through the North Sea and along the Iberian Peninsula, whilst those from the other more northerly populations tended to head west towards the mid-Atlantic staging area. Individuals from Svalbard staged much further west in the Atlantic during both migrations, where they may have encountered different, potentially more favourable, conditions given that the Svalbard population appears to be declining less severely than other populations in the north-east Atlantic.
Understanding where long-distance migrants, such as Arctic Skuas, are distributed during migration and the strategies they use is a vital first step in identifying threats that individuals may encounter en route, and how this may affect their survival, productivity and therefore population trends. This new knowledge will help us prioritise future research and conservation actions for this declining charismatic seabird.
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