1) HawkWatch International, 1800 South West Temple Suite 226, Salt Lake City, UT 84115 USA, 2) Audubon of Florida’s Tavernier Science Center, 115 Indian Mound Trail, FL 33070 Tavernier, USA, 3) Department of Biology, University of New Mexico, Castetter Hall, Albuquerque, NM 87131 USA, 4) Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, FL 32611 USA Oecologia (2003), V134, pp505–510, doi: 10.1007/s00442-002-1153-8 Estimating the latitudinal origins of migratory birds using hydrogen and sulfur stable isotopes in feathers: influence of marine prey base Casey A. Lott (1,2), Timothy D. Meehan (3) and Julie A. Heath (4) Hydrogen stable isotope analysis of feathers is an important tool for estimating the natal or breeding latitudes of nearctic-neotropical migratory birds. This method is based on the latitudinal variation of hydrogen stable isotope ratios in precipitation in North America (δDp) and the inheritance of this variation in newly formed feathers (δDf). We hypothesized that the typically strong relationship between δDp and δDf would be decoupled in birds that forage in marine food webs because marine waters have relatively high δD values compared to δD values for local precipitation. Birds that forage on marine prey bases should also have feathers with high δ34S values, since δ34S values for marine sulfate are generally higher than δ34S values in terrestrial systems. To examine this potential marine effect on feather stable isotope ratios, we measured δD and δ34S in the feathers of nine different species of raptors from both inland and coastal locations across North America.