Elephant Hair Keeps "Diary" of Diet, Migration
for National Geographic News
|January 4, 2006|
Researchers say they have traced the diets and migration patterns of
elephants in Kenya by examining the hair at the tips of their tails.
The method may help alleviate conflicts between humans and crop-raiding elephants, the scientists note.
Researchers studied elephants in the Samburu National Reserve from 2000 to 2002, fitting seven elephants with global positioning system (GPS) radio collars and collecting hair from the pachyderms' tails at various intervals.
The seven animals migrate from the semiarid region in and near the Samburu Reserve to the Imenti Forest on the flanks of Mount Kenya, 37 miles (60 kilometers) away.
The reserve rises about 3,000 feet (900 meters) above sea level. Its vegetation is largely acacia trees and scrub bush. In the Imenti Forest, found at an altitude of about 6,500 feet (2,000 meters), evergreen and deciduous trees dominate the landscape.
Researchers spotted six of the seven elephants in or near the Samburu National Reserve during the study's observation period from early 2001 to July 2002. GPS data corroborated their presence there.
But one elephant, an old bull designated B1013, had a very different pattern from February 2002 to July 2002.
It made three long trips from the arid lowlands to the upland forest near Mount Kenya and back, spending the rainy season in the lowlands and the dry season in the forest near the mountain.
This was not a gradual migration. The bull moved from one location to the othera distance of 25 miles (40 kilometers) as the crow fliesin less than 15 hours, a behavior called "streaking."
Analysis of B1013's hair showed that the bull ate a different diet depending on his location. But the data also revealed another essential fact: B1013 got a significant part of its diet by raiding crops cultivated in subsistence farms near the Imenti Forest.
The hair analysis gives more information than GPS data alone, according to Thure E. Cerling, a professor of geology and geophysics at the University of Utah and lead study author. "This is additional information," he said, "not meant to replace older methods, say GPS or direct observation, used to study elephants."
"It provides a detailed dietary history of individuals that cannot be obtained in any other way. So this may explain why animals migrate, not just the fact that they migrate."
Elephant hair can grow up to 20 inches (50 centimeters) long, and its rate of growth is about 0.01 to 0.04 inches (0.04 to 0.11 centimeters) a day. As a result, a single hair can hold clues to an elephant's diet and migration patterns spanning a year or more.
Elephants eat grass when it's available and browse on shrubs and trees at other times. These two kinds of plants undergo photosynthesis by different means.
The plants leave different chemical tracesspecifically ratios of carbon 12 and carbon 13in the hair of foraging animals.
The ratio changes quickly as the diet changes. Because of this, measuring fluctuating carbon ratios in elephant hair helps indicate what the animals recently ate. This applies to all mammals, not just elephants.
"This is a way to quantify dietgrass versus browseeven on animals with no observational information," Cerling said.
"In spite of all the observations made on elephants, the importance of grass versus browse has not been well quantified. Using elephant hair, we could find this out for many different habitats without having to make detailed observations in every one," he said.
"We simply needed a single hair from each of several different animals to characterize what is happening in a region, realizing the limitations, of course, of whatever sample size we have."
Keith Leggett, a researcher with the Wildlife Conservation Society's Northwestern Namibia Elephant and Giraffe Project, said the method is "a very interesting and innovative step in combining analytical chemistry and biology."
Still, he has some reservations. "All their data is based on knowing the rate of tail hair growth and that [the] growth was constant throughout the year," he said. "It could well be that growth is dependent on available nutrition and varied seasonally throughout the year."
Leggett also suggests that the researchers should have studied the hair growth of captive animals. "Elephants in the wild lose and break tail hair all the time. It would have definitely helped to have some data on tail hair growth from captured animals for comparison."
The study is described in the current online edition of the Proceedings of the National Academy of Sciences and will appear in the journal's January 10 print edition.
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