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

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We used an analysis of deuterium values (δD) 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 δD values in feathers of birds with known molt locations and birds with unknown molt locations. Mean feather value of δD was –24.8‰ (SD = 10.5‰, range = –48.0‰ to –5.5‰), 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 δD, and the geographic location of sample sites within the study area was selected as the best model. Feather δD values were higher than expected from mean growing-season rainfall δD values predicted for our study site. We discuss possible explanations for the enriched δD 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 δD values; information on diet gathered simultaneously with feather samples may be valuable for future studies.