Tigers, among the planet's most iconic and secretive creatures, have been near the top of the endangered list for some time. But yesterday, a landmark study by leading conservationists warned that their plight is even more serious than previously feared.

The big cat, the report warns, is close to extinction and the area in which it lives has been nearly halved in the last 10 years.

The area occupied by tigers is 41% smaller than 10 years ago and is just 7% of its historical "range" before habitat loss and hunting slashed its numbers, according to scientists at the Wildlife Conservation Society in New York, the World Wildlife Fund and the Smithsonian National Zoological Park in Washington. Tigers once ranged across Asia from eastern Turkey to the Russian far east.

In India, for example, where 60% of the world's tigers live, the population fell from 100,000 in the 19th century to 3,600 now. Many researchers believe the true figure is less than half the official estimate.

"The current trajectory will surely cause wild populations to disappear in many places, or shrink to the point of 'ecological extinction' - where their numbers are too few to play their role as the top predator," the authors write. "Now more than ever, tigers need homeland security." This grim prediction will come true in 20 years, the authors estimate, unless urgent action is taken.

The study is a follow-up to similar work carried out in 1995. It draws together satellite data on habitat type, information on poaching in different regions and data on tiger numbers.

Counting tigers is notoriously difficult because they are extremely secretive and very spread out. Data is collected either by counting paw prints or setting camera traps which snap unsuspecting tigers on their nightly prowl.

The study, paid for by the Save the Tiger Fund, identifies 76 "tiger conservation landscapes" - places with habitat which has the best chance of supporting viable tiger populations. Half would be able to support 100 tigers or more.

The grim headline figure is not simply a measure of how much tiger habitat has been destroyed since 1995, although much has been lost. The data take into account whether habitat that has become fragmented would be big enough to support a tiger population. The cats are reluctant to cross open areas and so need well connected forest. Also, it takes into account whether heavy poaching of the tigers' prey means that there would not be enough food for females to raise cubs.

"The last decade has been catastrophic for tigers and they simply can't afford another one like that," said Eric Dinerstein, chief scientist with WWF and one of the study's authors. But the news is not all bad, he said. "Like the Dow Jones, there are some stocks that are up while the rest are down."

The tiger population in the Russian far east, for example, has increased over the past half century from around 50 to 500. Also, the survey shows that targeted conservation efforts can pay off. "Just by applying a little bit of protection, they can rebound dramatically," said Dr Dinerstein. Tigers breed quickly for a large mammal and do not require pristine habitat to survive, so preventing poaching can lead to a rapid recovery of a local population. Apart from physical habitat destruction, the main threat comes from hunters. A tiger skin can fetch more than £5,000 and the penises, used in traditional Chinese medicine, are worth £14,000 a kilo.

"A lot of money is involved and a lot of people are involved," said Tito Joseph with the Wildlife Protection Society of India. Criminal gangs with links to drugs and arms trading smuggle tiger parts from India to China and Tibet. Skins are popular as garments called chubbas, and are also traded to collectors in the west.

Contrary to popular belief, tiger penises are not used as an aphrodisiac in Chinese medicine, but in cures for fevers and rheumatism. The Chinese government and NGOs are working with traditional medicine sellers to promote alternatives. The bones of a common mole rat called the sailong are now often used.

"There is cause for optimism," said Sabri Zain, advocacy and campaign director of Traffic, an NGO that combats illegal wildlife trade. "In terms of trade there is an appreciable reduction in demand for tiger bone-based medicine."

The authors of the report - Setting Priorities for the Conservation and Recovery of Wild Tigers 2005-2015 - advocate a "tiger summit", involving the heads of state of the 13 countries which still host the species. They believe this would galvanise political will and raise funds for conservation. To safeguard the remaining animals, the report says increased protection of the 20 most important tiger habitat areas should be a priority. Of the six tiger sub-species, the Javan tiger, Caspian tiger and Bali tiger have already become extinct.