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CONSERVATIONISTS may be miscalculating the numbers of threatened animals such
as elephants, say African and American researchers. The error occurs because of
a flaw in the way they estimate animal numbers from the piles of dung the
creatures leave behind.

The mistake could lead researchers to think that there are twice as many
elephants as there really are in some regions, according to Andrew Plumptre of
the Wildlife Conservation Society (WCS) in New York.

Biologist Katy Payne of Cornell University in Ithaca, New York, agrees. 鈥淲e
really need to know elephant numbers and the evidence that we have is all quite
indirect,鈥� says Payne, who electronically tracks elephants.

Counting elephants from aeroplanes is impossible in the vast, equatorial
rainforests of Central Africa. So researchers often estimate elephant numbers by
counting dung piles in a given area. They also need to know the rate at which
dung decays. Because it鈥檚 extremely difficult to determine these rates, however,
researchers tallying elephants in one region tend to rely on standard decay
rates established elsewhere.

But researchers at the WCS have found that this decay rate varies from region
to region depending on the climate and environment. Using the wrong values can
lead the census astray, says Plumptre.

He and his colleague Anthony Chifu Nchanji studied decaying elephant dung in
the forests of Banyang-Mbo Wildlife Sanctuary in southwest Cameroon. They found
that the dung decayed between 55 and 65 per cent more slowly than dung in the
rainforests of neighbouring Gabon. If researchers use decay rates from Gabon to
count elephants in Cameroon, they would probably find more elephants than are
actually around.

This could mean estimates in Cameroon at least twice as high as those derived
from decay rates calculated locally, says Plumptre. 鈥淗owever accurate your dung
density estimate, the decay rate can severely affect the result.鈥�

Plumptre also says that the dung-pile census should be carried out over a
region similar in size to an elephant鈥檚 natural range. The usual technique of
monitoring only small, protected areas distorts numbers because elephants move
in and out of these regions, he says. 鈥淚f the elephant population increases
within the protected area, you cannot determine whether it is a real increase or
whether it is due to elephants moving in because they are being poached
辞耻迟蝉颈诲别.鈥�

Plumptre says that similar problems may also plague other animal census
studies that rely on indirect evidence such as nests, tracks or burrows.