About 500,000sq-km of forests, including 39 tiger reserves in 17 states, are being surveyed.

"We would know the tiger numbers in Terrai, Central India and the Western Ghats by December. Although the estimation process for the entire country would be over only by March next year," professor Y.V. Jhala of Wildlife Institute of India (WII), told IANS.

He said: "Not only tiger reserves, but all forest areas in the country will be covered."

The last census in 2005-06 showed a sharp fall in tiger numbers. The census then conducted with an improved method revealed India had just 1,411 tigers left in the wild, raising serious concern about their survival.

Jhala said a new phase involving camera-trapping of tigers has begun. "Researchers have started this exercise, as the ground work involving the forest staff is almost completed."

Each camera costs about Rs10,000 and is especially designed for deployment in forests. It has censors that trigger the camera to take pictures automatically whenever animals come within range in front of its lens. They are usually attached to a tree. Batteries and the film of the camera are replaced manually when they run out. Since they are produced in small numbers in India, demand for large quantities is met through imports.

"The Indian Institute of Science produces them but only in limited number for research purpose," says Rahul Kaul, director of Wild Species Programme of the NGO Wildlife Trust of India, which will lay the camera-traps.