It is estimated there are 3200 tigers left worldwide - 95 per cent fewer than a century ago - and the booming wildlife trade is the biggest threat to their survival.
Increasing affluence in Asia has caused prices for skins and the body parts used in traditional Chinese medicines to soar. International gangs pay local Nepalese handsomely to kill tigers and rhinos. The skin and bones are handed to middlemen who pass easily through the porous border to India, where the big dealers are based. For many in a country where the average income is 150 Nepalese rupees ($2) a day, rewards of around $9560 a skin and $3250 a kilogram of bones outweigh the risks of being caught and jailed for up to 15 years.
Poachers kill tigers either using homemade guns fashioned from wood and piping which fire bullets of crushed glass and gunpowder, or by laying poisoned bait.
The WWF Nepal's co-ordinator for wildlife trade monitoring, Diwakar Chapagain, said: "It is hard to know if a tiger has been poached, because nothing is left behind. Each part of the animal has a sale value - eye-balls for drinks, the penis for soup to boost virility, its teeth for jewellery and its bones for good luck charms. Stuffed tiger cubs and rugs made from skins are also seen as status symbols."
Anti-poaching work has its dangers. Bardia assistant warden Ramesh Thapa has been targeted: "I got phone calls with death threats and then a middleman came to warn me that a hitman had been hired to kill me - the man knew me so he told me. I moved my wife and daughter from a village to Kathmandu."
The Nepal police's criminal investigation bureau established a wildlife unit only two years ago. Superintendent Pravin Pokharel, 38, led the 11-strong unit responsible for activity outside the nine vast national parks until last August. He believes 15 to 20 per cent of Nepalese wildlife crime is detected.
He said: "We have informants who tell us someone is dealing tiger skin or rhino horn. We go undercover as buyers and get evidence using spy recorders and video and we go through phone records. One year ago a dealer tried to sell an undercover officer a jute bag of bones from a whole tiger.
"During my time we arrested 100 people, mostly small-time dealers. The big dealers are in India. They use local tribespeople to kill to order."
Most of the plunder went to China.
"The price is increasing all the time. Two days ago two people with one rhino horn were asking 6 million Nepalese rupees in Chitwan. That would fetch 8 million rupees in Kathmandu, and that would be multiplied in China."
During Nepal's civil war between government forces and Maoist rebels from 1996 to 2006, the army checkpoints in the parks that had helped curb the wildlife trade were deserted after they became a prime target for the guerrillas. This resulted in a poaching bonanza, leaving Bardia with a handful of rhinos and tigers.
Now, thanks largely to conservation and anti-poaching programmes run by the WWF, tiger numbers are inching up. Last year it was estimated that there were 37 tigers in Bardia national park, up from 18 in 2009.
In 2010 the WWF started a multi-million dollar global Tigers Alive appeal with the aim of doubling the number by 2022. One of the areas where it is concentrating its efforts is the Terai Arc, 5 million hectares which includes Bardia national park on the border with India where around 120 royal Bengal tigers live near 8 million people.
The park now has 31 anti-poaching bases, and some are being provided with solar power so they can be manned around the clock. The WWF has also started a gun amnesty which has taken in hundreds of homemade guns - the village receives $6.70 for each weapon handed in.
One of the keys to boosting tiger numbers is to restore their habitat in "corridors" between the parks. Tigers have to be able to move freely between the parks so they can mate and catch prey.
Much of the WWF's work in Nepal involves harnessing the skills and enthusiasm of villagers so they can run anti-poaching patrols and conservation projects themselves.
In 2006, tigers had 40 per cent less habitat than they had 10 years earlier. Demand by villagers for wood for fuel and building, illegal logging, agricultural expansion and intensive grazing are all behind the erosion.
Twelve years ago the WWF started plantation and seedling protection programmes as well as micro-financing and insurance schemes to protect against livestock being killed.
There are now thousands of community forests, run by local people. Villagers have been helped to install biogas, reducing the need for firewood, and grazing is now limited.
The vice-chairman of the Community Forest Coordination Committee in the Khata corridor, Bhadai Tharu, lost an eye when he was attacked by a tiger while patrolling grasslands nine years ago. Asked what happened, he lunges forward, claws the air and lets rip a bellicose roar.
"A tiger jumped on me from a bush at about 1pm. My friends ran off," said Bhadai, 48, a father of three.
Removing his sunglasses - given to him by actor and wildlife campaigner Leonardo DiCaprio when he visited the area - he shows his scars.
Fearing for his life, he put all his strength into elbowing the animal.
"If I do nothing I would die. I made a loud roaring noise and the tiger ran off. Blood was pouring out of my eye. I was taken to hospital and my eye was only attached by one tiny nerve so it had to be removed. One of my ribs was taken out to reconstruct my face.
"I didn't have much to do with tiger conservation for two years after, but now if I don't see a tiger's paw mark every day I feel something is missing."
The Observer joined Bhadai and about 20 villagers - mainly women in their teens and 20s armed with sticks - on an anti-poaching patrol in the forest near Gauri.
Bhadai spotted some disturbed leaves and scattered them with a stick to reveal two iron traps; a large net was found nearby.
Harirani Chaudhary, 19, a student on the patrol, said: "Without a forest there's no life for us. That's why we conserve the forest and patrol. We must save the tiger, because the tiger is head of everything in the food chain. When we have lots of tigers, it means the habitat is strong enough to support all of us. Tourists will come and our village will improve."
A few months ago, seven tigers and nine rhino were photographed by automatic cameras set up in in the 3km-long Khata corridor.
Chapagain said: "Their appearance shows what is being done is working. Fifteen years ago the Khata corridor was barren land and bad forest and there were no tiger or rhino and only a few elephant."
That progress has been made is clear, but the battle to save the tigers is still far from won.
- Observer
