Using Stable Hydrogen Isotope Analyses of Avian Tissue to Infer Connectivity Among Populations of South American Austral Migrants
Keith A. Hobson (1, 3), Gabriel Bowen (2), Guillermo E. Pérez (3), Leonard Wassenaar (4)
1. Environment Canada, Prairie and Northern Wildlife Research Center, Canadian Wildlife Service, 115 Perimeter Road. Saskatoon, Saskatchewan, Canada, S7N 0X4.
E-mail: keith.hobson@ec.gc.ca
2. University of California, Department of Earth Sciences, 225 Sinsheimer, Santa Cruz, CA 95064.
3. University of Saskatchewan, Department of Biology, 112 Science Place, Saskatoon, Saskatchewan, Canada, S7N 0X4. E-mail: guillermo.perez@ec.gc.ca
4. Environment Canada, National Water Research Institute, 11 Innovation Boulevard, Saskatoon, Saskatchewan, S7N 3H5
Establishing seasonal patterns of movement of Austral migrants is crucial for our understanding of their life history, ecology, and behavior. Austral migrants breed in temperate latitudes of South America during the South American summers and move north towards the Neotropics to winter. Seasonal bird migration results in species spending different parts of their annual cycle in geographically and ecologically separate locations. Factors occurring at these different locations are likely to affect individual fitness and population dynamics. When dealing with small passerines, conventional tracking programs, such as leg banding and radio telemetry typically have not provided the necessary linkages between breeding, wintering and stopover sites. Fortunately, with advances in the use of hydrogen stable isotopes, as demonstrated for migrants in North America, now it is possible to track movements of migratory species that travel across continental or altitudinal isotopic gradients (see Hobson and Wassenaar 1997, Chamberlain et al. 1997, Kelly et al. 2002, Rubenstein et al. 2002, Rubenstein and Hobson 2004).
Patterns of deuterium (δD) in feathers and other tissues grown at locations across North America correlate well with long-term patterns of mean growing season δD values in precipitation. This phenomenon has lead to a number of successful applications to determine origins of Neotropical migrant songbirds breeding in North America. Similar isotopic applications are now emerging for migrants that breed in Europe (Hobson et al., in press). Here, we present an altitude-corrected depiction of the long-term growing season precipitation δD for South America (Fig 1).Using several examples of known Austral migrant movements, we demonstrate how these δD contours can be used to establish connectivity among populations (see examples). The essence of this approach is that the hydrogen isotope abundance in tissues of a consumer reflects their ultimate source of hydrogen in rainwater at that location. This forms the basis of all isotopic tracking of animals that move across isotopic gradients or between distinct isotopic foodwebs.
Emerging applications and advances in stable isotope techniques in North America and Europe provide an excellent alternative and template, to track Austral migrants that have latitudinal or altitudinal migration. We look forward to enquiries about this technique and its use to create migratory connectivity in South America. Our hope is open the doors to work in collaboration with South American researchers who seek answers to important conservation questions that require a quick and effective identification of migratory connectivity.
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