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Journal of Ornithology

, Volume 160, Issue 1, pp 239–248 | Cite as

Body condition of Eiders at Danish wintering grounds and at pre-breeding grounds in Åland

  • Karsten LaursenEmail author
  • Anders Pape Møller
  • Markus Öst
Original Article

Abstract

Breeding Eiders Somateria mollissima in the Baltic/Wadden Sea population have declined in recent decades, and several causes have been suggested. A recent study showed a modest increase in body mass from 2.20 kg by ca. 100 g during winter in Denmark, the main wintering area of the flyway population. This raises the question of whether Eiders could increase their body mass by an additional 200 g during pre-breeding to reach the average body mass of ca. 2.50 kg needed for successful reproduction. We analyzed this question by collecting Eiders at the Danish wintering grounds and pre-breeding grounds at Åland, Finland. Female Eiders increased their body condition (defined as scaled body mass index) from winter to the pre-breeding period, whereas males concurrently decreased in weight. The mean body mass of adult female Eiders was 2.23 kg in late winter, when they initiated spring migration. The mean female body mass at the pre-breeding grounds was 2.44 kg, an increase of 9.4% compared with females at the wintering grounds, while adult males decreased in weight by 3.4%. A decrease in gizzard mass was accompanied by a change in diet from large blue mussels Mytilus edulis at the wintering grounds to the small but more abundant mussels in the gizzard during pre-breeding. We conclude that female Eiders can reach a body mass of ca. 2.50 kg before breeding. Building up body condition for breeding is feasible at Åland; thus, difficulty in acquiring adequate resources for reproduction is unlikely to restrict local population size.

Keywords

Body condition Capital breeder Eiders Scaled body mass index Somateria mollissima 

Zusammenfassung

Körperkondition von Eiderenten in dänischen Wintergebieten und in vorbrutzeitlichen Rastgebieten auf Åland

Die baltische bzw. Wattenmeer-Brutpopulation von Eiderenten Somateria mollissima ist in den vergangenen Dekaden rückläufig. Verschiedene Gründe dafür wurden diskutiert. Eine aktuelle Studie zeigte eine leichte Zunahme der Körpermasse um ca. 100 g bei insgesamt 2,20 kg während des Winters in Dänemark, dem Hauptüberwinterungsgebiet dieser Flyway-Population. Dies brachte die Frage auf, ob Eiderenten in der Vorbrutphase ihre Körpermasse um zusätzliche 200 g erhöhen können, um ein für eine erfolgreiche Reproduktion benötigtes durchschnittliches Körpergewicht von ca. 2,5 kg zu erreichen. Wir untersuchten diese Frage, indem sowohl in den dänischen Wintergebieten als auch in den vorbrutzeitlichen Rastgebieten auf Åland Eiderenten gesammelt und gewogen wurden. Eiderenten-Weibchen steigerten ihre Körperkondition (definiert als skalierter Körpermasse Index) vom Winter in die Vorbrutzeit, wohingegen Männchen zeitgleich im Gewicht abnahmen. Die mittlere Körpermasse adulter Weibchen lag bei 2,23 kg im Spätwinter kurz vor Beginn des Frühjahrszuges. Die mittlere Körpermasse der Weibchen in den vorbrutzeitlichen Gebieten lag bei 2,44 kg, was einer Zunahme von 9,4% im Vergleich zu den Weibchen in den Wintergebieten entspricht. Adulte Männchen dagegen nahmen um 3,4% ab. Eine Abnahme des Muskelmagengewichtes ging einher mit einem Wechsel in der Nahrung von großen Miesmuscheln Mytilus edulis in den Wintergebieten hin zu kleinen jedoch reichlicher vorkommenden Muscheln im Muskelmagen während der Vorbrutphase. Wir schließen daraus, dass weibliche Eiderenten ein Körpergewicht von bis zu 2,50 kg vor der Brutzeit erreichen können. Der Aufbau von Körperkondition für das folgende Brutgeschäft ist auf Åland also möglich, so dass nicht anzunehmen ist, dass dortige Ressourcenknappheit die lokale Populationsgröße beeinflusst.

Notes

Acknowledgements

We thank Robin Juslin at Ålands Landskapsregering and hunters from Åland for collecting Eiders. We also thank the Danish hunters. Without the help of hunters this study would not have been possible. We obtained funding from the 15 June Foundation (ref. 2015-B-132) in Denmark (to K.L.) and the Swedish Cultural Foundation (ref. 2015-B-132) in Finland (to M.Ö.).

Supplementary material

10336_2018_1609_MOESM1_ESM.docx (14 kb)
Supplementary material 1 (DOCX 13 kb)

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Copyright information

© Dt. Ornithologen-Gesellschaft e.V. 2018

Authors and Affiliations

  • Karsten Laursen
    • 1
    Email author
  • Anders Pape Møller
    • 2
    • 3
  • Markus Öst
    • 4
  1. 1.Department of BioscienceAarhus UniversityRøndeDenmark
  2. 2.Ecologie Systématique EvolutionUniversité Paris-Sud, CNRSOrsayFrance
  3. 3.Agro Paris TechUniversité Paris-SaclayOrsay CedexFrance
  4. 4.Environmental and Marine Biology, Faculty of Science and EngineeringÅbo Akademi UniversityTurkuFinland

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