Improving Geochemical Methods for Assessing the Impacts of Anthropogenic Landscape Changes on Wildlife

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Hundreds of animal species make long-distance migrations, but details about the magnitude and specifics of such movements are often unknown. Issues related to geographic origins and migration of animals have attracted great attention in recent years because of an increasing need to understand the distributions and habitat requirements of species. Conventional tools for following animal movements over long-distances, such as transmitters, are not feasible on smaller animals because of technological limitations. Geochemical techniques offer an alternative approach for studying migration. This approach is based on the premise that animals sample their environs by incorporating geochemical signals into their tissues via diet and that such signals reflect consistent differences in landscape geochemistry. Increasing interest in the potential for geochemical methods to track the origins of plants and animals is emanating from disciplines as varied as public health (e.g., movement of avian influenza), economics (movement of harmful agricultural pests or invasive species), law enforcement (poaching, origins of plant-derived narcotics), and conservation (origins of migrants killed by wind turbines or other hazards caused by anthropogenic changes in land use). Stable isotope applications have gained widespread attention as a means of tracking migration and scores of animal movement studies using stable isotopes were published in the past decade. However, two underlying assumptions of such studies are that specific geographic areas have distinct stable isotope signatures (i.e., isoscapes) and that variation within the isoscape is limited through time and among individuals within the population occurring there. These assumptions have never been adequately tested. Validating such assumptions through detailed study of a population that is highly constrained in time and space would represent a novel contribution to our current understanding of isotope distributions in natural ecosystems, as well as the propagation of isoscape fingerprints into local and migratory populations of animals.