Differences in δ13C and δ15N values between feathers and blood of seabird chicks: implications for non-invasive isotopic investigations

Abstract

Blood and feathers are the most targeted tissues for isotopic investigations in avian ecology, primarily because they can be easily and non-destructively sampled on live individuals. Comparing blood and feather isotopic ratios can provide valuable information on dietary shifts, trophic specialization and migration patterns, but it requires a good knowledge of the isotopic differences between the two tissues. Here, δ13C and δ15N values of whole blood (in blood cells of a few species) and simultaneously grown body feathers were measured in seabird chicks to quantify the tissue-related isotopic differences. Seabirds include 27 populations of 22 wild species that were sampled in 2000–2008, and a review of the literature added 8 groups (including adult birds) to the analysis. The use of a large data set that overall encompasses wide δ13C and δ15N ranges allowed us to depict for the first time accurate relationships between blood and feather isotopic ratios across avian taxa. Blood was impoverished in 13C and generally in 15N compared with feathers. Both mean δ13C and δ15N values of feathers and blood were highly positively and linearly related [feather δ13C = 0.972 (±0.020) blood δ13C + 0.962 (±0.414), and feather δ15N = 1.014 (±0.056) blood + 0.447 (±0.665), respectively; both P < 0.0001]. The regressions should be applied to mathematically correct feather or whole blood δ13C and δ15N values when comparing isotopic ratios within and between ecological studies on birds.