Enriched feather hydrogen isotope values for Wood Thrushes sampled in Georgia, USA, during the breeding season: implications for quantifying dispersal

We used an analysis of deuterium values (delta D) of 151 Wood Thrush (Hylocichla mustelina (J.F. Gmelin, 1789)) feathers collected during the breeding season at the Piedmont National Wildlife Refuge in Georgia, USA, to determine fidelity to the study site. We compared delta D values in feathers of birds with known molt locations and birds with unknown molt locations. Mean feather value of delta D was -24.8 parts per thousand (SD = 10.5 parts per thousand, range= -48.0 parts per thousand to - 5.5 parts per thousand), and we were unable to determine a site-specific signature to assess fidelity of breeders within our sample. We used an information criterion approach to evaluate multiple hypotheses to explain the high variation in delta D, and the geographic location of sample sites within the study area was selected as the best model. Feather delta D values were higher than expected from mean growing-season rainfall delta D values predicted for our study site. We discuss possible explanations for the enriched delta D values and postulate that heat stress during molt may have contributed to our results. We suggest that future stable isotope data collection consider the potential for small-scale variation in feather delta D values; information on diet gathered simultaneously with feather samples may be valuable for future studies.