Growth Rates of Elephant Hair. Hair growth rates for male andfemale elephants are 0.55 ± 0.11 mm/day (9 hairs from5 individuals) and 0.81 ± 0.13 (23 hairs from 11 individuals),respectively, and are significantly different (ANOVA, P <0.0001). Within one individual, the growth rate of differenthairs may vary by up to 30%, but growth rates for a given hairappears to be constant to within 5–10%, which agrees withprevious observations for equids (10, 11). The overall rangein tail hair growth rates is from 0.4 to 1.1 mm per day, withsingle hair lengths sometimes exceeding 500 mm, thus preservingdiet or migration information for periods often exceeding 1year for a single hair.
Spatial Distribution and Stable Isotope Ratios. GPS radio collarswere fitted to the seven elephants (four female, three male)of this study in Samburu National Reserve in Northern Kenyain 2001 and 2002 (14). Six of the seven elephants were visuallyobserved to be in Samburu National Reserve or in the immediatevicinity during the observation period from early 2001 to July2002, and this was corroborated with the GPS information; thisgroup constitutes the Samburu resident elephants. However, oneelephant, an 40-year-old bull elephant (B1013), collared onFebruary 3, 2002, had a very different movement history thanthe Samburu resident elephants for the period from February2002 to July 2002. The GPS collar recorded the hourly positionsof B1013's movements between February 3, 2002 and July 18, 2002,when the collar failed. Unfortunately, B1013 was shot and killedshortly thereafter, and a second hair could not be recovered.During this period, B1013 made three major trips, shifting fromthe arid lowlands of Samburu National Reserve to the mesic Imentiupland forest near Mt. Kenya or vice versa. The periods spentin the lowlands correspond to the mid- and late rainy season,and periods spent in the forest were during the dry season.Each range shift was accomplished in <15 h, covering a straight-linedistance over 40 km, a behavior pattern described as "streaking"(14). It is assumed that B1013 moved in the same pattern in2001, when the isotope data are available from a single hair,as from February 2002 to July 2002, when the GPS data are available.
Stable isotope analyses at 5-mm intervals (13C and 15N) of thehair collected on February 3, 2002 showed that this individualoccupied two isotopically distinct regions (Fig. 1B). The 15Nrecords environmental information, including 15N values relatedto regional vegetation. The hair segments with elevated 15Nvalues (from 8 to 10.5) corresponded to values observed in residentelephants of Samburu National Reserve (average11 for the sametime period). Plants in the mesic highlands of the Aberdaresand Mt. Kenya region have 15N values averaging 1.7 ±0.5 (n = 21), whereas those in xeric lowlands of Samburu NationalReserve average 7.9 ± 0.7 (n = 14); these values aresignificantly different (ANOVA; P < 0.0001). Enrichment in15N for hair compared with diet is 3, suggesting that equilibrium15N values for these two regions should be 5 and 11, respectively.Moving as he did between the two regions, B1013 never attainedisotope equilibrium with the environment in either region. Thus,the movement data and the isotope data show that B1013 occupiedthe highlands (where the 15N values are low) in the dry season,and in the rainy season he moved to the lowlands, where 15Nvalues are elevated.
Seasonal Diet Changes. According to the chronology establishedhere, B1013 had four periods of increased consumption of C4grass. Three of these periods were associated with wet seasonsand periods of elevated remotely sensed NDVI values, representingincreased vegetative productivity. In general, African elephantshave a diet dominated by browse (6) and consume grass only asa windfall when it is in new growth. These periods of grassconsumption occurred when B1013 was observed in Samburu NationalReserve and when NDVI values exceeded 0.3. This pattern of elevatedC4 consumption during wet seasons was comparable with observedpatterns in resident Samburu elephants (Fig. 1C); during theseintervals, B1013 had similar C4 grass consumption as the othersix elephants. The single exception is the highest C4 consumptionpeak, which occurred during the dry season between June 18 andAugust 16, 2001. By comparison, the other six elephants hada low fraction of C4 grass consumption during this dry season.During this interval, while B1013 was in the Imenti Forest,average NDVI was low, yet C4 grasses made up 36% of the dietintegrated over this interval, with peak values approaching50% C4 biomass. NDVI in the Imenti region was below the yearlyaverage from June 11 to November 21, 2001, corresponding withthe dry season period when vegetative productivity is decreased.
GPS tracking data from the subsequent period spent in Imentireveals that, while in residence of the Imenti Forest, B1013was outside the forest reserve boundaries only during nighttimehours (Fig. 2). Most elephant crop raiding occurs at night,apparently to avoid human interaction (17, 18). Subsistencefarming occurs adjacent to the Imenti Forest (19), and thisregion, around the time of the data collection, was one of themajor crop raiding conflict zones in Kenya. Thus, it appearsthat this isotope signal is a quantifiable record of crop raiding(Fig. 3). While in the Imenti Forest, C3 vegetation was theprincipal food available, and therefore the C4 component ofdiet was most likely obtained from adjacent crops, evidentlyat night. During the dry season between June and August of 2001,our study indicates that B1013 was supplementing his C3 forestdiet with nocturnal crop raiding of C4 maize. Fig. 3 shows adetailed stable isotope profile along with the estimated fractionationC4 intake during this unusual C4 diet period during the longdry season of 2001.
Quantification of longitudinal diet records from hair in wildanimals can offer important information to conservationistsand wildlife managers. This article provides an example of oneof the many possible uses that stable isotopes can provide inresolving the elephant–human conflict issue. Despite therecording of conflict incidences, it is often difficult to understandelephant decisions made at an individual level and to quantifythe dietary importance of crop raiding by elephants. Combiningstudies of elephant movement patterns and overall diet withincidences of raiding injects additional scientific data intothe highly topical discussion of human–elephant conflictalleviation.