Stable sulphur isotope (delta S-34) ratios in bird feathers from India indicate strong segregation between the Himalaya and Gangetic plain, and the rest of India

Although stable hydrogen (delta H-2) and carbon (delta C-13) isotopic compositions of bird feathers have been increasingly used to understand the migration of birds through assignment of individuals to established isoscapes, far less is known about the structure of feather isoscapes based on stable sulphur isotope (delta S-34) assays. While delta H-2 isoscapes have been used to investigate the migratory origins of the Globe Skimmer (Pantala flavescens) dragonfly in India, no isotope studies have been applied to avian migration patterns in that region. Here, based on museum collections, we report the feather delta S-34 values of 13 avian species that included marine birds with expected S-34 enriched feathers, resident birds throughout India and a single migratory species, Bar-headed Goose (Anser indicus). Feathers from the marine birds were the most enriched (20.6 +/- 1.2 parts per thousand, n = 10; range = 4.4 parts per thousand) in S-34 but terrestrial resident species also showed unexpectedly high delta S-34 values (11.7 +/- 4.8 parts per thousand, n = 74; range = 19.9 parts per thousand) throughout most of India but the Himalayan region and Gangetic plain typically showed delta S-34 values less than 6.4 parts per thousand. Our results show the utility of feather delta S-34 studies to decipher avian and other animal migration between these two regions.