Sulfur isotopic discrimination factors differ among avian tissues and diets: Insights from a case study in Gentoo Penguins (Pygoscelis papua)

The use of stable isotopes of sulfur (δ34S) to infer avian diets, foraging habitats, and movements is relatively uncommon, resulting in a lack of information on patterns of δ34S incorporation in avian tissue. In a controlled study of Gentoo Penguins (Pygoscelis papua), we found that diet-tissue isotopic discrimination factors (Δ34Sdiet-tissue) differed among egg components and feathers synthesized from a common diet, ranging from -0.4 to -1.7 ‰. We also found that methodical choices such as lipid extraction and prey tissue selection influenced calculated Δ34Sdiet-tissue values. Specifically, Δ34Sdiet-tissue values were lower (i.e., more negative) when calculated using whole fish relative to fish muscle and lipid-extraction biased egg yolk, but not fish tissue, δ34S values. Δ34Sdiet-tissue values obtained for Gentoo Penguins fed a marine fish diet were generally lower than those reported for freshwater-fish-consuming Double-crested Cormorants (Phalacrocorax auritus), the only other bird ...