Don ' t Count onDung

"Conservationists（自然保护主义者）maybe miscalculating the numbers of the threatened animals such

aselephants."say African and American researchers.The error occurs becauseof a flaw in the way that they

estimate animalnumbers 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

someregions,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 ele-

phant numbers andthe evidence that we have is quite indirect,"says Payne,who electronically

tracks elephants.

Counting elephantsfrom planes is impossible in the vast rainforests of Central Africa. So researchers of-

ten estimateelephant numbers by counting dung piles in a given area.They also need to knowthe rate at

which dungdecays.Because it's extremely difficult to determine these rates,researcherscounting elephants

in one region tendto rely on standard decay rates established elsewhere.

But researchers atthe WCS have found that this decay rate varies from region to region dependingon the

climate andenvironment. " 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 of Came-

roon.They found thatthe dung decayed between 55 and 65 per cent more slowly than the dung in the

rainforests ofneighbouring Gabon.If researchers use decay rates from Gabon to count elephants in Cameroon,

they would probablyfind more elephants than are actually around."This could mean estimates inCameroon

are at least twiceas high as those derived from decay rates calculated locally,"saysPlumptre."However

accurate your dungdensity estimate might be,the decay rate can severely affect the result."

Plumptre also saysthat the dung-pile census should be carried out over a region similar in sizeto an ele-

phant's naturalrange."The usual technique of monitoring only small,protected areasdistorts numbers be-

cause elephants movein and out of these regions,"he says."If the elephant populationincreases within the

protected area,youcannot determine whether it is a real increase or whether it is due toelephants 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 evi--

dence such asnests,tracks or burrows（地洞）.Theword"threatened"in the first sentence of the first paragraph could bebest replaced by_________.

A."endangered"

B."frightened"

C."killed"

D."angered"