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A system that uses paw prints and faeces offers scientists a fresh way to determine how many tigers are left in the wild, a study has suggested.

Scientists hope the new technique will provide a low-cost and reliable way to accurately assess big cat numbers.

Fewer than 3,500 tigers remain in the wild, with more than half found in India where the population is spread over more than 100,000 sq km of forest.

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"Tigers are cryptic, nocturnal and occur at low densities so they are extremely difficult to monitor," said lead author Yadvendradev Jhala from the Wildlife Institute of India.

"Unless we know how many tigers are left in the wild, and whether their numbers are increasing or decreasing, we will not be able to conserve them," he added.

Current monitoring methods include using camera traps or looking for paw prints.

"In the absence of abundance information, conservation management decisions are often based on crude estimates, expert opinion or educated guesses - which may result in erroneous decisions that can be counterproductive," the India-based team observed.

While paw prints, otherwise known as pugmarks, allow individual tigers to be identified, scientists say they are not a reliable way to estimate a region's overall population.

Camera traps offer a much more accurate assessment of an area's tiger density, but the technique is expensive and labour intensive, resulting in its deployment being limited to places that have a relatively high number of the big cats.

'Basmati rice'

"By showing that it is possible to accurately estimate tiger numbers from their paw prints and faeces, we have opened up a new way of cost-effectively keeping our finger on the pulse of the tiger population and gauging the success of conservation programmes," explained Dr Jhala.

"This approach could be applied to monitoring other endangered species across vast landscapes," he added.

Between 2006 and 2007, Dr Jhala and his team gathered samples from 18 tiger populations at 21 locations across central and northern India, recording the occurrence of pugmarks and faeces.

"Tiger faeces are the size of large beetroots and have a characteristic pungent, musky odour," he explained.

"Fresh tiger faeces are normally accompanied by urine sprays that smell like well-cooked basmati rice."

Tigers are solitary animals, and use the spray to mark their territory - hence the presence of scat offered an insight into the species density in the area.

When the team compared its findings with data from camera traps, the group found the new system provided similar results but for just 7% of the cost.

Writing in the British Ecology Society journal, the team concluded: "The approach and models... permit rapid and cost-effective assessments of abundance to monitor the status of tigers at landscape scales.

"This information is vital for conservation investment, habitat management, planning development projects, formulation of policy and for law enforcement."