"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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