Dietary reconstructions of Slender-billed Gull fledglings based on blood δ13C and δ15N values.

Stable isotope values for whole blood of Slender-billed Gull fledglings as a function of year (2001–2004) and breeding site (saltmines of Sanlúcar -SM-, the fish farm of Veta la Palma -FF- and natural marshes of Doñana -NM-). Pair-wise comparisons were done through Tamhane’s test procedure (overall alpha level of 0.05); identical superscript numbers indicate homogeneous sub-groups. Relative importance (95% Bayesian Credibility Intervals, BCI) of food from the three sites (SM, FF and NM) in the diet of fledglings hatched at different sites and in different years was inferred through a Bayesian double-isotope (δ13C and δ15N) isotopic mixing model (SIAR, [29]).