Estimating origins of short-distance migrant songbirds in North America: Contrasting inferences from hydrogen isotope measurements of feathers, claws, and blood

Tracing movements of migratory birds between breeding and wintering areas is important for both theoretical and conservation purposes. Intrinsic markers such as stable isotopes have received considerable attention because of their usefulness for evaluating migratory connections without the need to mark and recapture individuals. Establishing migratory linkages using stable-isotope markers hinges on knowing which tissues most accurately reflect the isotopic signature of previous feeding locations of interest. Here, we assessed the correspondence among stable-hydrogen isotope (delta D) values of feathers. claws, and cellular portions of blood from migrating White-throated Sparrows (Zonotrichia albicollis) to determine if these measures provided concordant estimates of origins. delta D values of claws from birds captured during spring and fall migration were positively correlated with delta D values of head feathers grown on the winterine, grounds and tail feathers grown on breeding grounds, respectively, indicating that claws contained information on origins of individuals. However, analyses contrasting delta D measurements of base and tip of claws, and head and tail feathers suggest that a significant amount of claw growth occurred during migration resulting in biased estimates of breeding and wintering origins. Thus, for ground-foraging birds like White-throated Sparrows, we caution against using isotope measurements Of claws as long-term position indicators. delta D values of blood were correlated with the delta D values from the base of claws, which represented the most recent claw growth. but were not correlated with the delta D values of claw tips and head feathers. Thus, it appears that the delta D values of blood cells are not useful for estimating wintering latitudes of White-throated Sparrows captured during spring migration.