Unexpected dietary preferences of Eurasian Spoonbills in the Dutch Wadden Sea: spoonbills mainly feed on small fish not shrimp

Jeltje Jouta*, Petra de Goeij, Tamar Lok, Estefania Velilla, Cornelis J. Camphuysen, Mardik Leopold, Henk W. van der Veer, Han Olff, Otto Overdijk, Theunis Piersma

*Corresponding author for this work

    Research output: Contribution to JournalArticleAcademicpeer-review

    Abstract

    After an historical absence, over the last decades Eurasian Spoonbills Platalea leucorodia leucorodia have returned to breed on the barrier islands of the Wadden Sea. The area offers an abundance of predator-free nesting habitat, low degrees of disturbance, and an extensive intertidal feeding area with increasing stocks of brown shrimp Crangon crangon, the assumed main prey of P. leucorodia leucorodia. Nevertheless, newly established and expanding colonies of spoonbills have surprisingly quickly reached plateau levels. Here we tested the often stated assertion that spoonbills mainly rely on brown shrimp as food, by quantifying the diet of chicks on the basis of regurgitates and by analysis of blood isotopes using stable isotope Bayesian mixing models. Both methods showed that, rather than brown shrimp being the staple food of spoonbill chicks, small flatfish (especially plaice Pleuronectes platessa) and gobies (Pomatoschistus spp.) were their main prey. Unlike shrimp, small flatfish have been reported to be rather scarce in the Wadden Sea in recent years, which may explain the rapid saturation of colony size due to food-related density-dependent recruitment declines of growing colonies. By way of their diet and colony growth characteristics, spoonbills may thus indicate the availability of small fish in the Wadden Sea. We predict that the recovery to former densities of young flatfish and other juvenile/small fish in the Wadden Sea will be tracked by changing diets (more fish) and an increase in the size of Eurasian Spoonbill colonies across the Wadden Sea.

    Original languageEnglish
    Pages (from-to)839-849
    Number of pages11
    JournalJournal of Ornithology
    Volume159
    Issue number3
    DOIs
    Publication statusPublished - 1 Jul 2018

    Funding

    Acknowledgements This study would not have been possible without the participation of Eric Menkveld, Carl Zuhorn, Arjan Zonderland, Oene de Jong, Richard Kiewiet, the late Frits Oud, and Erik Jansen (nature managers on the Wadden Islands; It Fryske Gea, Natuurmonu-menten and Staatsbosbeheer) and all spoonbill volunteers, especially Harry Horn and Roos Kentie. We thank Rebecca Reurslag for her help with the regurgitate analyses; Stefan Schouten, Thomas Leerink and Kevin Donkers (NIOZ) for technical assistance with the stable isotope analyses; and Sarina Jung for the population trends of Gobiidae. We are grateful to Stefan Schouten for giving us advanced isotopic advice. The fieldwork was carried out under Dutch welfare (DEC) protocol RuG-4752 amendement D. This study was carried out as part of the Waddensleutels (WF203930) and Metawad (WF209925) projects, both supported by the Waddenfonds.

    FundersFunder number
    Not added10914

      Keywords

      • Bayesian mixing models
      • Intertidal
      • Platalea leucorodia leucorodia
      • Regurgitate analysis
      • Restoration
      • Stable isotope analysis in R

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