GIS-based model of stable hydrogen isotope ratios in North American growing-season precipitation for use in animal movement studies.

Stable hydrogen isotope ratios of precipitation (deltaD(p)) show distinct geographic patterns across North America. Over the last decade, ecologists have utilized growing-season deltaD(p) patterns to study the movements of migratory animals. The accuracy and precision of such studies is, in part, contingent upon the accuracy and precision of growing-season deltaD(p) maps. Previous mapping efforts have employed simple kriging procedures to produce smooth contor maps of growing-season deltaD(p). We attempted to improve these maps by incorporating the effects of altitude on both deltaD(p) values and growing season length. This involved producing elevation-corrected monthly deltaD(p), temperature, and precipitation amount values for 1-km grid cells across the continental United States and Canada using recently developed interpolation procedures. We used a geographic information system (GIS) to calculate a weighted-average growing-season deltaD(p) value for each grid cell using deltaD(p) and precipitation amount values for all months in which the mean temperature was greater than 0 degrees C. We used seven independent data sets to compare the precision of the resulting altitude-corrected map with another that did not account for altitude. Overall, predicted deltaD(p) values from the altitude-corrected map more closely matched observed values, and correspondence was more pronounced at finer spatial scales. Digital versions of the GIS-based maps generated during this effort are available via the Internet at http://biology.unm.edu/wolf/precipitationD.htm. These deltaD(p) layers can be combined with other types of spatial information, such as species' geographic ranges and habitat associations, to further improve our understanding of animal movements.