Animal ecology through Stable Isotope Analysis

Stable Isotope Ratios techniques raised in the last thirty years as a novel approach very useful for researchers and ecologists that intend to deepen into manifold aspects of animal ecology. In particular, isotopic ratios in animal tissues ultimately reflect diet, and the isotopic composition of diet reflects biogeochemical attributes of environments that may, in turn, show spatial structure and pattern, both at local and continental scale. Here, SIRs techniques were applied to birds, and, in particular, the stable isotope ratios of hydrogen, carbon, nitrogen, oxygen and sulfur were determined in bird feathers. The study was articulated in three different case studies. In the first two studies, SIRs technique was applied to migratory birds, sampled during postbreeding migration on Italian Alps. In particular, feathers were sampled on juvenile Passerines captured in some ringing stations of ‘Progetto Alpi’ long-term monitoring project. The focus was put both on commonly and less commonly observed species (more than 800 individuals of 48 species). The first study aimed to determine the geographical breeding origin of migrants using the stable isotope ratios of hydrogen and oxygen. The study allowed 1) to perform an analyses on the relationship between hydrogen and oxygen isotope ratios of several species, 2) to verify whether migratory populations have distinct geographical origins, different timing of passage and a comparison between species. To achieve the aims, a recovery data set was also used. The second study focused on the application of stable isotope ratios of carbon, nitrogen and sulfur to infer the trophic attitudes of different passerine species during the breeding season. In this study more species were analyzed, aiming to understand if isotopic variability of carbon, nitrogen and sulfur were able to distinguish trophic relationships between species which have similar diets. It was found that species are isotopically different grouping them for migratory phenology. These first two studies want to be a start point to better understand migrant trends across the Alps and Europe, and to improve knowledge in using stable isotopes in European continent. The third case study focused on lesser kestrel breeding ecology in the Gela Plain, in Sicily. In particular the stable isotope ratios of hydrogen, carbon, nitrogen, oxygen and sulfur were measured in feathers of nestlings. The aim of this study was to delineate the isotopic fingerprint of the hunting areas of their parents, making possible to distinguish different spatial uses of adults within and between colonies, and verifying if different habitat selected may be translated into distinct isotopic composition in keratinous tissues. Findings underlined the potential that a multi-isotope approach has in studying animal ecology, especially in detecting trophic partitioning and habitat selection at local and regional scale.