African elephants in Kenyas Samburu National Reserve. Note the adult elephants tail hair. University of Utah geochemist Thure Cerling analyzed chemical isotopes in elephant tail hair to help track the diet and movements of the giant creatures, which have international status as endangered animals. Credit: George Wittemyer
New tracking method may help endangered pachyderms
By analyzing chemicals in tail hair from elephants that wore radio collars, researchers tracked the diet and movements of elephants in Kenya – a method aimed at reducing human-elephant conflicts and determining where to establish sanctuaries to protect the endangered creatures.
"This is a new method to understand elephant behavior and help ensure their survival," says geochemist Thure Cerling, the study’s principal author and a distinguished professor of geology-geophysics and biology at the University of Utah.
So a section of elephant tail hair with a low carbon-13-to-carbon-12 ratio indicates the elephant was eating trees and shrubs at the time that section of hair grew, while a high ratio indicates they ate tropical grasses – or perhaps a crop like corn.
The Findings: You (Elephants) Are What You Eat
The scientists studied tail hair isotopes and-or GPS tracking records for seven elephants during 2000 through July 2002.
Isotopes in the tail hair of six elephants had high ratios of nitrogen-15 to nitrogen-14, indicating they spent their time in the arid lowlands of Samburu. Most of the time, they had low ratios of carbon-13 to carbon-12, indicating they ate trees and shrubs. But during the rainy season – as indicated by satellite photos – they had higher ratios of carbon-13 to carbon-12 because they ate grasses that flourished in the wet weather.
"When it gets green, they begin to eat grass," Cerling says. "When it’s not, they eat trees and shrubs."
The seventh elephant – the bull named Lewis – was different. Cerling had isotope data from Lewis’ tail hair from 2000 through February 2002, when the hair was removed at the same time a GPS radio collar was placed on Lewis. The collar tracked Lewis from February to July 2002, when it failed. An assumption was made that Lewis’s behavior when GPS tracked him was similar to when he was "tracked" by his tail hair chemistry.
The collar showed that Lewis spent rainy seasons in lowland Samburu, but then trekked 25 miles cross country to the Imenti Forest, some 6,500 feet in elevation on Mount Kenya. While in the forest, he made nighttime raids into subsistence farms.
The collar showed Lewis made three trips between mountain forest and arid lowlands between February and July 2002, with each 25-mile trek taking only 15 hours.
Such behavior is called "streaking" because the elephants "are essentially going as fast as they can," Cerling says. "They spend their time in one area, and suddenly make this dash across the country and spend a long time in another area. Fewer and fewer elephants do this because the distance between safe areas is getting greater and there are more fences, more guns and more people."
Lewis’ tail hairs showed he had higher nitrogen-15-to-nitrogen-14 ratios during times he was in the arid Samburu preserve, which produces the "dry" nitrogen isotope signature even during the rainy season. Lewis also had higher ratios of carbon-13 to carbon-12, indicating he went to Samburu during rainy times to eat grass.
At other times, the nitrogen isotope ratio was lower in Lewis’ tail hair, indicating he spent the dry season in the mountains, where he normally ate trees and shrubs. But elevated carbon isotope ratios from mid-June to mid-August 2001 showed Lewis was eating C4 plants too – probably maize during nighttime crop raids.
Cerling says it is "important to quantify how much of elephants’ diet comes from crops. It’s going to help resolve elephant-human conflict by quantifying the crop damage done by elephants. … Areas open to elephants are getting smaller and smaller, so we need to know how important different foods are to their diets in different areas."
Lewis’ Deadly Final Trek
Douglas-Hamilton says that when elephants move, it is for "sustenance, security or sex." Lewis’ motivation was not security since he crossed dangerous human-occupied territory. But by "streaking" to the mountains during the dry season, Lewis was able to eat corn while the Samburu elephants browsed on trees and shrubs.
"Diet is very important for bull elephants," says Douglas-Hamilton. "If they are to succeed in sexual contests for females, they need high-quality food to build up their strength, hence the reason for high-risk crop raiding."
"It is a high-risk, high-gain strategy, and in our elephant’s case it did not pay off. Shortly after the research was done, Lewis suffered multiple gunshots, very likely a result of crop raiding. He died in the Samburu reserve a year after the research was done."
Douglas-Hamilton says the study shows that "tracking stable isotopes in an elephant’s diet – when combined with actual tracking of movements using high-tech remote sensing – provides a powerful new tool for conservationists. It allows us to understand possible elephant motivation and, from this, to see how management plans can be focused on understanding their basic needs for space."
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