On the use of stable oxygen isotope (δ18O) measurements for tracking avian movements in North America

摘要

Tracking migratory animals has benefitted using measurements of naturally occurring stable isotopes of hydrogen (δ²H) in keratinous tissues such as hair and feathers to link animal origins to continental patterns or isoscapes of δ²H in precipitation. However, for most taxa, much less information exists on the use of stable oxygen isotope ratios (δ¹⁸O) despite the fact that δ²H and δ¹⁸O are strongly linked in environmental waters through the meteoric relationship and the possibility of using both isotopes to infer greater information on origins and climatic conditions where tissues are grown. A fundamental requirement of using stable isotopes to assign individuals and populations to origins is the development of a rescaling function linking environmental food web signals to the tissue of interest and for birds, this has not been carried out. Here, we derived the relationship between H and O isotopes in known source feathers of 104 individuals representing 11 species of insectivorous passerines sampled across the strong precipitation isoscape of North America. We determined again a strong expected relationship between feather δ²H (δ²Hf) and long-term amount-weighted precipitation δ²H (δ²Hp; r² = 0.77), but the corresponding relationship between δ¹⁸Of and δ¹⁸Op was poor (r² = 0.32) for the same samples. This suggests that δ²H measurements are currently more useful for assignment of insectivorous songbirds to precipitation isoscapes but does not preclude other uses of the δ¹⁸Of data. Currently, mechanisms responsible for the decoupling of H and O isotopes in food webs is poorly known, and we advocate a much broader sampling of both isotopes in the same keratinous tissues across precipitation isotope gradients and across taxa to resolve this issue and to increase the power of using water isotopes to track migratory animals.