| Stable isotope ratios of carbon (13C/12C, delta 13C), nitrogen (15N/14N, delta 15N) and hydrogen (D/H, deltaD) measured in feathers have shown promise as an intrinsic marker of origin for birds. Biological and physical processes vary among locations, causing stable isotope ratios to vary accordingly. Stable isotope ratios inherent in the environment will be reflected permanently in feathers, which become metabolically inert following growth. As long as a feather is retained, its stable isotope ratios can serve as a marker of its origin, and thus a marker of the bird's previous location. Passerines typically grow flight feathers on the breeding grounds, then retain the feathers until after the following breeding season. Stable isotope ratios in feathers have been used to link breeding and wintering locations, and they can potentially document natal and breeding dispersal. Because of the difficulty in tracing the movements of small birds, this important information is generally lacking. In that the use of stable isotopes in feathers is a newly emerging discipline, I attempted to document some potential sources of variation in feather stable isotope ratios. I measured differences in delta13C, delta 15N, and deltaD between feather shafts and vanes; among various types of flight feathers from the same bird; and within and among groups of siblings from a single location. Feather shafts and vanes differed in terms of all 3 stable isotope ratios, indicating a need for standardization of procedures among laboratories. I also measured variation among years, species, and discrete locations, and I developed regressions predicting deltaD and delta 13C based on the latitude at which they were grown. Stable isotope ratios did not differ among years, but species differed in terms of delta 15N and deltaD, the latter being an unexpected result based on previous studies. I used the regression of deltaD on latitude to predict the origins of breeding male indigo buntings, in order to determine natal and breeding dispersal. Natal dispersal was more frequent, and involved longer distances. This procedure yields a minimum dispersal distance, as only north-south movements are documented, but it may serve as an index of dispersal, allowing comparisons of species, age classes, or sexes. |
