Habitat destruction is forcing India's endangered tigers to new grounds, including high mountains which have a sufficient prey base but are not known to be the natural home of the big cats.

With forests in the foothills being built over and cleared for farming, wildlife experts say tigers are being increasingly spotted in high altitudes in India's northeast and west.

But they say tigers could still be as endangered in their new environment and are not as adaptable as leopards.

"Tigers can feel the effect of villages on the bio-diversity from miles, and move away," said Belinda Wright of the Wildlife Protection Society of India.

"But they are not as adaptable as leopards in mountains." India's wildlife crisis, highlighted best by the dwindling tiger and lion population, has caused huge national concern, pushing authorities to declare new measures to save the cats.

Experts say increasing human interference such as development, encroachment and destruction of habitat, as well as poaching, are the main threats to animals across India, from the Himalayas to Indian Ocean islands.

India is thought to be home to half the world's surviving tigers, but according to a census in 2001 and 2002, their numbers have dwindled to between 1,300 and 1,500 from 40,000 a century ago.

In an example of the tiger adapting to the threat to their natural habitat, experts have found at least 20 of them in the high mountains of Neora, tucked between Bhutan and India's eastern state of West Bengal.

"Until 1998, we found one or two tigers straying into the Neora from the foothills, but now they live there," said Pranabes Sanyal of World Conservation Union, who conducted a study on tiger migration.

The tigers moved to the dense cover of bamboo and oak at Neora from the Gorumara reserve in the foothills, their original habitat.