Is the double sampling tiger census accurate?

The people of India are being counted one by one for the ongoing population census, but our national animal is much more elusive. The just-completed tiger census - which estimates that about 1706 big cats roam the wild - involves a double sampling process that the government says is accurate. Some experts are not too convinced.

The census collected field data in the first phase using standardised protocols, aiming to cover all major tiger occupancy areas, explained Y.V. Jhala, the senior wildlife scientist from the Wildlife Institute of India who coordinated the Rs. 9.1 crore census exercise.

Information on tiger signs, prey availability, habitat conditions and human disturbances were collected in almost 30,000 forest “beats” or patrolling units, with forest personnel walking 6.25 lakh km to gather the data. Satellite telemetry data was also used.

Then a camera trapping method was used in select sample areas covering 10,500 square km, which amounts to about five per cent of the total area. A total of 800 camera traps were set up for about 50 days in every four square kilometres, and photographs were ultimately clicked of 615 individual tigers, which were identified their unique stripe patterns.

“The camera trap intensity of one per 4 sq km is the highest in the world,” said Dr. Jhala, adding that the extrapolation from 615 photographed tigers to an estimate of 1706 was based on peer-reviewed methodology standardised in the 2006 census.

‘Deficiencies in methodology’

However, K. Ullas Karanth, a well-known scientist and conservationist who heads the Centre for Wildlife Studies in Bangalore, says that “the full process of how these tiger numbers are generated for individual tiger populations and landscapes, has not been made public in a scientifically acceptable manner.” He found “serious deficiencies” in the partial methodologies which were published in the sole scientific paper on the subject, he said.

While he was unwilling to comment on the specifics of this year’s census figures, he sounded sceptical about the growth trends reversing the earlier shrinkage of tiger populations. “Since various threats faced by tigers do not appear to have diminished in last four years, it is difficult to explain the claimed reversal of the decline of tigers,” he said.

Tiger conservationist Valmik Thapar was also sceptical of large growth claims, saying that the new areas surveyed in this year’s exercise, such as the Sunderbans and some Naxal areas, accounted for much of the increase.

While admitting that many tigers had fallen victim to poaching and other dangers in the last couple of years, Environment Minister Jairam Ramesh said that growth was still possible due to unreported tiger births. “Tiger mortality is headlines. But when it comes to tiger fertility, nobody bothers about it,” he said.

Dr. Karanth suggested that intensive annual monitoring, using camera traps and DNA sampling, of the crucial source populations - reproducing tigers are found in just 10 per cent of their habitat - would be more effective than the unwieldy and expensive all-India census exercises that are only conducted once every four years. He also urged the government to bring in outside expertise to ensure reliability and transparency.