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Résumé :
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We used stable isotope tracers in the growing primary feathers of Eurasian Spoonbill chicks (Platalea leucorodia leucorodia) to study seasonal variation in their diet on one of the Frisian islands, Schiermonnikoog, The Netherlands. Using growing individual primaries as natural samplers over time, samples were taken along the length of primary feathers to estimate both within- and between-individual variation in diet. Absolute isotopic ratios of feather material ranged from -26.2 to -14.7 aEuro degrees for carbon (delta C-13) and from 13.0 to 18.7 aEuro degrees for nitrogen (delta N-15). The variation in delta C-13 values suggests the use of a variety of feeding habitats, ranging from freshwater to marine. Across the breeding season, there was a shift from predominantly freshwater prey early on to a more marine diet later in the season. Surprisingly, this shift did not occur within the growth trajectory of early born chicks which instead showed the opposite, but it did occur within individual chicks born later in the season. Stable isotope Bayesian mixing-model (SIAR) outcomes demonstrated that the freshwater/brackish prey had the highest isotopic contribution "(51 %;
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