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Last Updated: Wednesday, 7 November 2007, 10:54 GMT
How do you count tigers?
WHO, WHAT, WHY?
The Magazine answers...

Large tiger, photo by FW Champion
Caught on film by an early camera trap
India is lining up a "tiger protection force" to try to prevent poachers forcing the animal into extinction. New figures put numbers at less than 1,500. But how do experts count the big cats?

As any visitor to India's wildernesses will tell you, the beautiful Bengal tiger is an elusive beast. You might hear one, see its droppings or spot its footprints in the mud, but few clap eyes on one.

Even for experts, arriving at an accurate estimate of their numbers is a huge challenge. First they have to find the tigers, or evidence of them, then be sure they haven't counted the same one twice. With tiger numbers at such a critical low, it is crucial to know how many remain.

THE ANSWER
Camera traps that take a picture of the tiger are being used again, along with other tactics
"You need 30 to 40 breeding females and 10 to 20 males to form a viable population," says Valmik Thapar, one of India's leading conservationists. "Otherwise in-breeding becomes a problem."

The authorities also need to gain a clear picture of the extent of poaching - the biggest threat to tigers. The latest figures are based on data collected using a variety of techniques from radio-collaring to camera trapping. Numbers are gathered for an area of 100sq km then extrapolated to give an estimate for a wider area.

Caught on film

Camera trapping - getting the animal to set off a camera to take a picture of itself - was pioneered in the 1920s by Englishman FW Champion, a forester with the Imperial Forestry Service in India.

Tiger with long face, photo by FW Champion
A tripwire triggers the camera
Using tripwires and flash, Champion obtained dozens of remarkable photographs of tigers at night, as well as other passing wildlife.

Champion was fascinated by tigers and hated having to issue permits to dignitaries who came to his area of forest to shoot them. "He often gave out permits for areas where he knew there weren't any tigers," says his grandson James Champion, who is researching his grandfather's life for a book.

A rare early conservationist who detailed his experiences with tigers in two books still used by foresters today, Champion recognised that with good photographs of the animals, it was possible to tell individuals apart by their different stripe patterns.

But since tigers numbered tens of thousands at the time, there was little need for counting and the idea of using photography for that purpose seems to have been lost in the mists of time.

WHO, WHAT, WHY?
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A regular part of the BBC News Magazine, Who, What, Why? aims to answer some of the questions behind the headlines
By the 70s tiger numbers had been decimated by hunting, habitat loss and poaching. Then Prime Minister Indira Gandhi outlawed hunting and launched Project Tiger in an effort to save India's most impressive beast.

Scientists involved in the project used a technique called the "pugmark method" - taking plastercasts of tiger footprints and measuring them - to provide data on the tiger population. But the technique had many pitfalls; it's difficult to get a good foot impression in hard soil or by a waterhole, and how to tell how many cubs in a litter when all their footprints would be roughly the same size?

Thirty years on, many experts began to realise using pugmarks alone was unreliable and began arguing for more sophisticated means. Camera trapping came back into fashion.

Slimmer tigress, photo by FW Champion
Each tiger has different stripes
Now cameras are set off by more advanced methods than Champion's tripwires, and photos show both sides of the animal, making identifying and comparing them much easier.

Using these photos along with signals sent by radio collars, conservationists behind the recent national survey in India have gained more accurate data than ever before and the sad truth has emerged - a tiger population that many fear is on the brink of dying out.

"I had a meeting with the Prime Minster [Manmohan Singh] the other day and I didn't mince my words one tiny bit. I told him we are heading for extinction, so let's see what happens," says Valmik Thapar.

FW Champion would doubtless be delighted to know camera trapping is being used again, but horrified that numbers have dropped so low.

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