Refining isotopic tools to trace avian migratory origins and nutrient allocation strategies

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Effective study and conservation of migratory birds and other animals requires that migratory connections be made between all phases of the annual cycle. This task is complicated by the difficulties in tracking individual movements, especially of small bodied organisms. The use of naturally occurring stable isotopes of several elements that show spatial patterns across landscapes and continents (isoscapes) has revolutionized studies of migration since the approach does not require initial marking of individuals but relies instead on the measurement of endogenous isotopic fingerprints to assign individuals to origin. This approach is based on the fact that naturally occurring stable isotope ratios in the environment are transported in a predictable fashion to higher-order consumers. This proposal aims at improving our ability to assign individuals to isoscapes, especially those based on isotopic signatures present in precipitation (i.e. 2H/1H, 18O/16O) by determining key factors that contribute to within- and between-species isotopic patterns in feather keratins. This will be accomplished by Ph.D. student projects largely through the careful measurement of diet, drinking water, feathers and claws of captively raised birds and through the widespread assay of wild birds from known origins. A second component of the work will focus on using the same isotopic fingerprinting approach (but this time with 13C/12C and 15N/14N) to trace pathways of nutrients to eggs. This will allow the quantitative modeling of both endogenous and exogenous contributions of proteins and lipids to reproduction. Such an approach will allow the direct testing of the strategies migratory birds use in either transporting "capital" to their breeding sites or relying on local environments (i.e. "income") to fuel reproduction. Finally, a field-based program to trace nutrient allocations by high Arctic breeding geese to their eggs will be accomplished by a postdoctoral fellow during the last two years of the proposal. Together, these projects will move the whole field of isotopic ecology forward by allowing us to anticipate and model sources of isotopic variation in avian systems.