Don't Count on Dung（粪便）

Conservationists（自然保护主义者）may be miscalculating thenumbers of the threatened animals such as elephants,say African and Americanresearchers. The error

occurs because of aflaw in the way they estimate animal numbers from the piles of dung（粪）the creatures leave behind.

The mistake couldlead researchers to think that there are twice as many elephants as therereally are in some regions according to Andrew Plumptre of the Wildlife

ConservationSociety(WCS)in New York.

Biologist Katy Payneof Cornell Universityin Ithaca,New York,agrees,"We really need to know elephantnumbers and the evidence that we have is quite indirect,"says

Payne,whoelectronically tracks elephants.

Counting elephantsfrom planes is impossible in the vast rainforests of Central Africa. So researchers often estimate elephant numbers by countingdung piles in a given area.

They also need toknow the rate at which dung decays because it's extremely difficult todetermine these rates. However,researchers counting elephants in one regiontend to

rely on standarddecay rates established elsewhere.

But researchers atthe WCS have found that this decay rate varies from region to region dependingon the climate and environment. "Using the wrong values can lead the

census astray（离开正道）,"says Plumptre.

He and his colleagueAnthony Chifu Nchanji studied decaying elephant dung in the forests ofCameroon.They found that the dung decayed between 55 and 65 percent more

slowly than the dungin the rainforests of neighbouring Gabon.If researchers use decay rates from Gabon to count elephants in Cameroon,they would probably findmore

elephants than areactually around.This could mean estimates in Cameroon are at least twice ashigh as those derived from decay rates calculated locally,says

Plumptre"Howeveraccurate your dung density estimate might be,the decay rate can severely affectthe result."

Plumptre also saysthat the dung-pile census should be carried out over a region similar in sizeto an elephant's natural range.The usual technique of monitoring only

small,protectedareas distorts numbers because elephants move in and out of these regions,hesays"If the elephant population increases within the protected area,youcannot

determine whether itis a real increase or whether it is due to elephants moving in because they arebeing poached（入侵偷猎）outside."

Plumptre says thatsimilar problems may also affect other animal census studies that rely onindirect evidence such as nests,tracks or burrows（地洞）.According toPlumptre,the region over which a dung-pile census is carried out should be______.

A.small enough

B.well protected

C.carefullymonitored

D.large enough