Stable isotopes in elephant hair document migration patterns and diet changes
Thure E. Cerling *, 
, 
, George Wittemyer 
, Henrik B. Rasmussen ¶, Fritz Vollrath ¶, Claire E. Cerling , Todd J. Robinson , and Iain Douglas-Hamilton ||
*Department of Geology and Geophysics, 135 South 1460 East, University of Utah, Salt Lake City, UT 84112; Department of Biology, 257 South 1400 East, University of Utah, Salt Lake City, UT 84112; University of California, Berkeley, CA 94720; ¶Department of Zoology, Oxford University, Oxford OX1 3PS, United Kingdom; and ||Save The Elephants Foundation, Nairobi, Kenya
Contributed by Thure E. Cerling, November 4, 2005
We use chronologies of stable isotopes measured from elephant (Loxodonta africana) hair to determine migration patterns and seasonal diet changes in elephants in and near Samburu National Reserve in northern Kenya. Stable carbon isotopes record diet changes, principally enabling differentiation between browse and tropical grasses, which use the C3 and C4 photosynthetic pathways, respectively; stable nitrogen isotopes record regional patterns related to aridity, offering insight into localized ranging behavior. Isotopically identified range shifts were corroborated by global positioning system radio tracking data of the studied individuals. Comparison of the stable isotope record in the hair of one migrant individual with that of a resident population shows important differences in feeding and ranging behavior over time. Our analysis indicates that differences are the result of excursions into mesic environments coupled with intermittent crop raiding by the migrant individual. Variation in diet, quantified by using stable isotopes, can offer insight into diet-related wildlife behavior.
13-carbon | 15-nitrogen | chronology | human–elephant conflict
(Introduction)
The stable isotope ratios of 13C/12C in hair records the diet of mammals (1–4). It is particularly useful in distinguishing diets of C3 browse versus C4 grass in tropical regions (5–7) because of the large difference in 13C/12C ratios between plants using the C3 and C4 photosynthetic pathways, respectively. In tropical regions, the C3 pathway is used primarily by trees and shrubs, whereas plants using the C4 pathway are principally grasses (8, 9).
Hair is a particularly useful indicator of diet change (3, 4) because the isotope turnover of mammal tissues is high enough to resolve short-term diet changes. Recent advances in methodology, progressed through the study of large mammals with controlled diet changes (10, 11), allows detailed reconstruction of the diet history of individual large mammals in wild populations (12, 13).
In this study, we determine the growth rates and stable 13C/12C and 15N/14N ratios in elephant hair collected between 2001 and 2004. We focus on the behavior of a resident population of Samburu National Reserve, Northern Kenya, for the time period of 2000 to 2002. We compare stable isotope results of this resident population with a migrant elephant (B1013) that visited Samburu Reserve up to several times each year. Differences in isotope ratios between the resident individuals and the migrant indicate different behaviors, including rapid migration across long distances by the migrant individual and differences in the fraction C4 biomass in the diet. The latter may be related to seasonal crop raiding, which can be quantified by using stable isotope ratios.
Source: PNAS, January 10, 2006, vol. 103, no. 2, 371-373
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