Sulfur isotopic discrimination factors differ among avian tissues and diets: Insights from a case study in Gentoo Penguins.

This article focuses on quantifying sulfur isotopic discrimination factors (Δ³⁴S diet–tissue) between diet and avian tissues using a controlled study of Gentoo Penguins (Pygoscelis papua). The researchers found that Δ³⁴S diet–tissue values varied among egg components and feathers, ranging from –0.4‰ to –1.7‰, and were influenced by methodological factors such as lipid extraction and prey tissue selection (whole fish versus fish muscle). Compared to previous data on Double-crested Cormorants (Phalacrocorax auritus) consuming freshwater fish, Gentoo Penguins fed a marine fish diet exhibited generally lower Δ³⁴S diet–tissue values, supporting an inverse relationship between dietary δ³⁴S values and discrimination factors similar to that observed in mammals. The study provides recommendations for future research to improve the application of sulfur stable isotope analysis in ornithological dietary and ecological studies.