Skuas (Stercorarius spp.) moult body feathers during both the breeding and inter-breeding periods: implications for stable isotope investigations in seabirds

• Published in: Ibis
• Main Authors: Grana, Grilli, Cherel, Yves
• Other Authors: Instituto Nacional de Investigaciones en Biodiversidad y Medioambiente Bariloche (INIBIOMA-CONICET), Consejo Nacional de Investigaciones Científicas y Técnicas Buenos Aires (CONICET)-Universidad Nacional del Comahue Neuquén (UNCOMA), Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2017
• Subjects: Antarctica; diet; migration; Southern Ocean; [SDE]Environmental Sciences; Antarctic; The Antarctic; King George Island; Antarc*; antarcticus; Stercorarius antarcticus; Stercorarius maccormicki
• Online Access: https://hal.science/hal-01500534; https://doi.org/10.1111/ibi.12441

International audience Seabirds are mostly thought to moult during the inter-breeding period and the isotopicvalues of their feathers are often therefore assumed to relate to their assimilated diet duringsuch periods. We observed Brown Skuas Stercorarius antarcticus lonnbergi and SouthPolar Skuas Stercorarius maccormicki moulting on a breeding site at King George Island,Antarctica. This raises concerns about the reliability of using stable isotopes in feathersto infer feeding localities of birds during the inter-breeding period. We analysed thed13C and d15N values of growing and fully grown body feathers collected from the sameindividuals. For both species, d13C values of growing feathers indicated feeding areas inthe Antarctic zone (breeding grounds), whereas most fully grown feathers (100% forSouth Polar Skuas and 93.3% for Brown Skuas) could be assigned to northern latitudes(non-breeding grounds). However, a few fully grown body feathers of Brown Skuas(6.7% of the feathers, belonging to two birds) showed isotopic values that indicatedmoult in the Antarctic zone. As the growth period of those feathers was unknown, theycould not be used with confidence to depict the foraging behaviour of the birds duringthe non-breeding period. Although precautions must be taken when inferring dietaryinformation from feathers in seabirds where the moulting pattern is unknown, this studyshows that if the development stage of a feather (growing/fully grown) is identified, thendietary information from both breeding and non-breeding seasons can be obtained onthe same individual birds.