We thank J. R. Ehleringer and the Stable Isotope Ratio Facility for Environmental Research (SIRFER) at the University of Utah, the government of Kenya for permission to work in Kenya, the Kenya Wildlife Service for facilitation, Save The Elephants for technical and logistical field support, and the Packard Foundation.
Author contributions: T.E.C., G.W., H.B.R., F.V., and I.D.-H. designed research; T.E.C., G.W., H.B.R., F.V., C.E.C., T.J.R., and I.D.-H. performed research; T.E.C., G.W., and I.D.-H. analyzed data; and T.E.C. and G.W. wrote the paper.
Conflict of interest statement: No conflicts declared.
Abbreviations: GPS, Global Positioning System; NDVI, normalized differential vegetation index.
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© 2006 by The National Academy of Sciences of the USA