A feather hydrogen isoscape for Mexico Keith A. Hobson a, ⁎, Steven L. Van Wilgenburg b , Keith Larson c , Leonard I. Wassenaar a a Environment Canada, 11 Innovation Blvd., Saskatoon, Saskatchewan, Canada S7N 3H5 b Environment Canada, 115 Perimeter Road, Saskatoon, Saskatchewan, Canada S7N 0X4 c Department of Biology, University of Lund, Lund, Sweden abstract article info Article history: Received 13 June 2008 Accepted 3 February 2009 Available online 10 July 2009 Keywords: Deuterium Feather Groundwater House Sparrow Isoscape Mexico Developing useful biological isoscapes for areas of the world is a priority. This is the case for Mexico that hosts a large percentage of North America's Neotropical migrant birds. Here we investigated the use of House Sparrow (Passer domesticus) feathers to create a spatially explicit feather deuterium isoscape for that country using samples (n =461) that were collected across Mexico. Considerable and useful spatial hydrogen isotopic structure was observed, suggesting that isotopes may be a potential forensic tool for evaluating origins of Mexican derived fauna and flora. The most positive feather δD values occurred in the northeast and most negative in the south-central part of the country, roughly matching δD patterns observed in groundwater. A weak negative isotopic relationship was found with altitude in both the Pacific and Atlantic drainage systems. The most parsimonious model describing isotopic spatial variation in feathers between 300 and 3000 m a.s.l. included groundwater δD (δD gw ; precipitation proxy), sex, amount of precipitation, and the coefficient of variation in amount of precipitation. Overall, δD gw was a poor predictor of sparrow δD f values for all of Mexico. However, this relationship was considerably strengthened when we considered sex separately, removed the Baja peninsula from our sample, and considered the Atlantic and Pacific drainage basins separately. The strongest relationship between δD gw and δD f was found for female sparrows in the Atlantic drainage basin (r 2 =0.464). We recommend that researchers interested in inferring origins of migratory birds and other animals in Mexico create species specific isotopic basemaps that may be guided by the isotopic patterns we have observed for House Sparrows and groundwater. © 2009 Published by Elsevier B.V. 1. Introduction Fundamental to the practical application of “isoscapes” for tracking migrant organisms over large geospatial scales is that fixed tissue stable isotope values can be directly linked to geographical regions of known origin (Hobson and Wassenaar, 2008). For Neotropical migrant birds, these tissues are often feathers formed in the northern summer breeding or southern wintering sites. The isotopic composition (e.g. 13 C, 15 N, 2 H) of tissue is linked to discrete and continuous underlying spatial geological or hydrological isotopic patterns through local diet and foodwebs. To date, the long-term growing-season average patterns in the hydrogen isotopic composition of rainfall (δD p ) at continental scales have proven to provide the most useful predictable spatial foundation for biological samples (Bowen et al., 2005; Hobson 2008). For example, in North America the strong latitudinal gradient in δD p across much of the USA and Canada is directly reflected in feathers (δD f ) grown by birds prior to migration. This hydrosphere– biosphere isotopic linkage provides a powerful means of inferring origins of individuals captured elsewhere (Kelly et al. 2002; Rubenstein et al. 2002; Hobson et al. 2006, 2007). Currently, the strength of the relationship between δD p and δD f has defined the utility of the isotope approach for tracking migrant birds. It is clear that such relationships will be influenced initially by our ability to accurately predict δD p for a given year and region, by the degree to which δD p reflects the δD value of local waters most relevant during the time of feather or tissue growth, and by ecological and physiological processes that may alter the relationship between these two parameters for the focal species. Despite several examples showing excellent and robust correlations between δD p and δD f in temperate regions of North America, much more research is required to elucidate the nature of the variance associated with such regressions (Hobson 2008; Wunder and Norris 2008). In addition, while some regions (e.g. central Europe) have reasonably good isotopic coverage of rainfall, other areas (Africa, Asia, high-latitude regions) have relatively poor data coverage. In North America, Mexico is represented by only two IAEA Global Network for Isotopes in Precipitation (GNIP) stations, and the complex terrain of that country makes an interpolated δD p basemap as a starting point problematic. This is unfortunate because Mexico hosts one of the greatest proportions of all Neotropical migrant songbirds that annually migrate there from temperate areas in the USA and Canada to winter (Petit et al. 1995). Knowledge of the patterns of δD/δ 18 O in rain and Journal of Geochemical Exploration 102 (2009) 167–174 DOI of original article: 10.1016/j.gexplo.2009.02.002. ⁎ Corresponding author. Tel.: +1 306 975 4102; fax: +1 306 975 5143. E-mail address: Keith.Hobson@ec.gc.ca (K.A. Hobson). 0375-6742/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.gexplo.2009.02.007 Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/jgeoexp