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

Abstract

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.