an elephant’s tail hair tells its life story
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An elephant’s tail hair tells its life story

Researchers report that they were able to trace the diets and migration patterns of elephants in Kenya by examining the hair at the tips of the elephants’ tails. Among other benefits, this method might help to alleviate conflicts between humans and crop-raiding elephants.

Scientists 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 times throughout the study period.

The seven animals migrate from the semi-arid region in and near the Samburu Reserve to the Imenti Forest on the flanks of Mount Kenya, 37 miles away. The reserve is about 3,000 feet above sea level, with vegetation consisting largely of acacia trees and scrub bush. In the Imenti Forest, at an altitude of about 6,500 feet, the landscape is dominated by evergreen and deciduous trees.

During an observation period from February to June 2002, researches spotted six of the seven elephants in or near the Samburu National Reserve (their sightings were confirmed by GPS data.) One elephant, however, had a very different migration pattern.

An old bull, designated B1013, made three long trips from the lowlands to the upland forest near Mount Kenya and back, spending the rainy season in the lowlands and the dry season in the forest.

His migration was nothing like gradual – the bull moved from one location to the other, a distance of 25 miles as the crow flies, in less than 15 hours, a behavior known as ‘streaking.’

Analysis of B1013’s tail hair showed that the bull ate very differently depending on his location. It also became clear that he got a significant part of his diet by raiding crops cultivated in subsistence farms near the Imenti Forest.

Elephant hair can grow up to 20 inches long, at a rate of growth of 0.01 to 0.04 inches a day. As a result, a single hair can provide clues to an elephant’s diet and migration patterns for the period of a year or more.

Elephants eat grass when it’s available, and browse on shrubs and trees at other times. Because these two kinds of plants undergo photosynthesis by different means, they leave different chemical traces – specifically rations of carbon 12 and carbon 12 – in the hair of foraging animals. The ratio changes quickly as the animal’s diet changes; so measuring fluctuating carbon ratios in elephant hair helps indicate what the animal recently ate. This method can apply to all mammals, not just elephants.

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 author of the study. “This is additional information,” he said, “not meant to replace older methods like GPS or direct observation. But this is a way to quantify diet – grass versus browse – even on animals with no observational information. Such a detailed dietary history of individuals cannot be obtained in any other way. So this may explain why animals migrate, not just the fact that they do migrate at all.”

In spite of all the observation made of elephants, the importance of grass versus browse has not yet been well quantified. Cerling hopes that using elephant hair might illuminate these details for many different habitats, without having to make detailed observations in every one.

“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.”

Some researchers still have some reservations about the hair-use method. Keith Leggett, 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.”

However, “all their data is based on knowing the rate of tail hair growth and that the growth was constant throughout the year.” This data is imperfect, in his opinion, because that growth might be dependent on available nutrition and thus vary seasonally throughout the year.

Leggett also suggests that the researchers should have studied the hair growth of captive elephants, who are less likely regularly to lose and break tail hair than animals in the wild.

The study will appear in the Proceedings of the National Academy of Sciences journal’s January 10 print edition.

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