Using stable isotopes to associate migratory shorebirds with their wintering locations in Argentina

Abstract

We are evaluating the use of stable isotopes to identify the wintering areas of Neotropical migratory shorebirds in Argentina. Our goal is to associate individual birds, captured on the breeding grounds or in migration with specific winter sites, thereby helping to identify distinct areas used by different subpopulations. In January and February 2002 and 2003, we collected flight feathers from shorebirds at 23 wintering sites distributed across seven province s in Argentina (n = 170). Feathers samples were pre- pared and analyzed for δ 13 C, δ 15 N, δ 34 S, δ 18 O and δD by continuous flow methods. A discriminant function based on deuterium alone was not an accurate predictor of a shorebird’s province of origin, ranging from 8% correct (Santiago del Estero) to 80% correct (San ta Cruz). When other isotopes were included, the prediction accuracy increased substantially (from 56% in Buenos Aires to 100% in Tucumán). The improvement in accuracy was due to C/N, which separated D-depleted sites in the Andes from those in the south, and the inclusion of S separated sites with respect to their distance from the Atlantic. We also were able to correctly discriminate shorebirds from among two closely spaced sites within the province of Tierra del Fuego. These results suggest the feasibility of identifying the origin of a shorebird at a provincial level of accuracy, as well as uniquely identifying birds from some closely spaced sites. There is a high degree of intra- and inter-bird variability, especially in the Pampas region, where there is wide variety of wetland/water conditions. In that important shorebird region, the variability itself may in fact be the “signature.” Future addition of trace elements to the analyses may improve predictions based solely on stable isotopes.