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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