Tracing origins and migration of wildlife using stable isotopes: a review

To understand the ecology of migratory animals it is important to link geographic regions used by individuals including breeding, wintering, and intermediate stopover sites. Previous conventional approaches used to track animal movements have relied on extrinsic markers and typically the subsequent recovery of individuals. This approach has generally been inappropriate for most small, or non-game animals. The use of intrinsic markers such as fatty acid profiles, molecular DNA analyses, and the measurement of naturally occurring stable isotopes in animal tissues offer alternative approaches. This paper reviews the use of stable isotope analyses (primarily δ¹³C, δ¹⁵N, δ³⁴S, δD, δ⁸⁷Sr) to trace nutritional origin and migration in animals. This approach relies on the fact that foodweb isotopic signatures are reflected in the tissues of organisms and that such signatures can vary spatially based on a variety of biogeochemical processes. Organisms moving between isotopically distinct foodwebs can carry with them information on the location of previous feeding. Such an approach has been used to track animal use of inshore versus offshore, marine versus freshwater, terrestrial C₃ versus marine, terrestrial mesic versus xeric, and C₃ versus C₄ or Crassulacean acid metabolism foodwebs. More recently, the use of stable hydrogen isotope analyses (δD) to link organisms to broad geographic origin in North America is based on large-scale isotopic contours of growing-season average δD values in precipitation. This technique, especially when combined with the assay of other stable isotopes, will be extremely useful in helping to track migration and movement of a wide range of animals from insects to birds and mammals. Future research to refine our understanding of natural and anthropogenic-induced isotopic gradients in nature, and to explore the use of stable isotopes of other elements, is recommended.