Diets of Kenyan elephants from stable isotopes and the origin of confiscated ivory in Kenya Thure E. Cerling 1 *, Patrick Omondi 2 and Anthony N. Macharia 3 1 Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112-0111, U.S.A., 2 Kenya Wildlife Service, PO Box 40141- 00100, Nairobi, Kenya and 3 Department of Biology, University of Utah, Salt Lake City, UT 84112-0111, U.S.A. Abstract Stable isotopes provide information on the history of indi- vidual animals, which can include spatial information. We analysed over 300 ivory and bioapatite samples from ele- phants and hippopotamus for d 13 C and d 18 O in the context of spatial variability. Elephant and hippopotamus could be distinguished on the basis of d 13 C because elephants are predominantly browsers while hippopotamus are primarily grazers. Comparison of different elephant populations in Kenya shows that d 13 C and d 18 O are different in different regions because of different diet preferences and different sources of water. The Amboseli elephants have the highest percentage of grass in the diets of extant African elephants. Ivory from Central African elephants is significantly depleted in 13 C because of photosynthesis under closed- canopy conditions, and this distinction is used to show that much of the confiscated ivory carvings in Kenya are compatible with a Central African source. Key words: carbon-13, nitrogen-15, oxygen-18, Loxodonta africana, East Africa Re ´sume ´ Les isotopes stables fournissent sur l’histoire individuelle des animaux des informations qui peuvent comprendre des informations spatiales. Nous avons analyse ´, pour les d 13 C et d 18 O, plus de 300 e ´chantillons d’ivoire et de bioapatite d’e ´le ´phants et d’hippopotames, dans le contexte de la variabilite ´ spatiale. Les e ´le ´phants peuvent e ˆtre distingue ´s des hippopotames sur la base du d 13 C parce que les e ´le ´- phants mangent surtout des aliments pris a ` une certaine hauteur tandis que les hippos broutent principalement de l’herbe. La comparaison de diffe ´rentes populations d’e ´le ´- phants au Kenya montre que les d 13 C et d 18 O sont diffe ´- rents dans des re ´gions diffe ´rentes en raison de pre ´fe ´rences alimentaires et de sources d’eau diffe ´rentes. Les e ´le ´phants d’Amboseli ont le plus grand pourcentage d’herbe dans leur re ´gime alimentaire de tous les e ´le ´phants vivant en Afrique. L’ivoire des e ´le ´phants d’Afrique centrale est sig- nificativement pauvre en 13 C en raison de la photos- ynthe `se qui s’effectue sous une canope ´e ferme ´e, et cette distinction sert a ` montrer qu’une grande partie des sculptures d’ivoire confisque ´es au Kenya sont compatibles avec une source centrafricaine. Introduction Mammalian diets are recorded by the stable isotope ratio of carbon and oxygen in animal tissues. The 13 C/ 12 C ratio is different in plants using the C 3 photosynthetic pathway, which is used by most dicotyledenous plants (dicots), than do those plants using the C 4 photosynthetic pathway, which are predominantly grasses and sedges (monocoty- ledonous plants, or monocots). Likewise, the 18 O/ 16 O ratio in water and plants is related to temperature of precipita- tion and subsequent evaporation, so that areas that are hot and dry have higher 18 O/ 16 O ratios in plant and sur- face waters than do regions that are cooler and wetter. The 13 C/ 12 C and 18 O/ 16 O ratios of food and water are passed along to the consumer and these ratios can be used to understand the fraction of C 3 (dicots) or C 4 (grasses) bio- mass in the diets of mammals (DeNiro & Epstein, 1978; Koch et al., 1995; Cerling & Harris, 1999; Cerling, Harris & Leakey, 1999; Cerling, Harris & Passey, 2003). Stable isotopes have been used to determine geographic patterns of ivory sourcing and to estimate the fraction of grass in the diets of elephants on a regional basis (van der Merwe, Lee-Thorp & Bell, 1988; Vogel et al., 1990; van der Merwe et al., 1990; Koch et al., 1995; Cerling et al., 1999). Almost all tropical dicots use the C 3 photosynthetic pathway and have d 13 C values ranging from about )24 to )35&, *Correspondence: E-mail: tcerling@mines.utah.edu 614 Ó 2007 The Authors. Journal compilation Ó 2007 Blackwell Publishing Ltd, Afr. J. Ecol., 45, 614–623