By Daniel Lak BBC Nepal correspondent in Chitwan National Park

Deep in the thick teak forest here, dozens of elephants are crashing through the undergrowth.

The usual pristine calm of a spring morning has been rudely shattered.

"Rhino one to rhino two, do you see the quarry, come in please," shouts a man with a walkie-talkie.

He ducks as the elephant he is riding carries him under a low-hanging tree branch.

So far 77 rhinos have been moved from Chitwan

The message comes back on the radio - a young male rhinoceros has been spotted.

The elephants begin to move towards it, their mahouts, or drivers, steering them by touching their ears with bare feet.

This is nothing less than a big game hunt - about 100 people, borne by 30 elephants, chasing one greater Asian one-horned rhinoceros.

But these are not poachers or animal killers - they are conservationists from the Nepal department of National Parks, the Worldwide Fund for Nature and the King Mahendra Trust for Nature Conservation.

As they force the young male rhino out in the open, the guns that point towards the fleeing beast are loaded with syringe-like darts, full of muscle relaxant.

Finally, Dr Tirtha Man Maskey, head of the national parks department and the very first warden of Royal Chitwan National Park when it was created in 1973, gets a clear shot.

His mahout holds the elephant steady and he pulls the trigger.

Drugged

The rhino jumps as the dart hits his flank, then starts to move towards the bank of the River Rapti.

The elephants follow in a long line, herding the beast into open ground.

The rhino population of Chitwan is going up by nearly 4% a year

Tirtha Man Maskey, Nepal national parks

The rhino stops, slumps and then slowly his two-tonne bulk sags to the ground.

He is paralysed by the powerful drug in the dart.

"Hurry now," cautions hunt organiser Shanta Raj Jnawali, "we've got 40 minutes to get him in the crate."

For that is what is going on here - the round up of 10 rhinos from Chitwan park and their transportation to Bardia National Park, 400 kilometres (250 miles) to the west.

"The rhino population of Chitwan is going up by nearly 4% a year," says Dr Maskey,

"While in Bardia there are less than 100. We're creating a viable breeding population there and taking pressure off the environment and villagers here."

Nepal has successfully moved 77 rhinos from Chitwan to other parks in the country since the so-called "translocation" programme began in 1986.

Rhino rage

Chitwan has nearly 550 rhinos living in an area that saw the population drop below 100 just 40 years ago.

By any measure, it's a huge success.

The downed rhino is rolled by about 20 labourers onto a sledge, gently but with determination.

Rhino numbers have dwindled over the years

The drug has only 20 minutes left before it wears off, and angry rhinos are best avoided.

They kill several people around Chitwan every year.

The sledge is dragged by tractor to a wooden crate near several trucks that are to take the rhinos to Bardia, driving through the night so the captured animals don't suffer from the heat of the day.

They refuse to eat or drink in captivity, and as the trucks drive you can hear them bellow with rage and drive their horns into the side of the crate.

Poachers

Finally, at Bardia, before an audience of local army officers, the sliding wooden door at the end of the crate is opened, and the rhinos back out slowly.

One bangs its head into the truck as it makes for the river for a drink and a bath.

Rhinos kill several people in Nepal every year

Last year, a vehicle was damaged.

Rhinos can run at 40 km/h and weigh as much as any small car.

The officers and conservationists in Bardia's Babai Valley applaud as the rhinos run away, free to roam and - with luck - breed and raise young.

This area had a big rhino population 300 years ago, but it dwindled with human settlement and poaching.

Now the challenge is to keep the beasts safe from poachers with the same skill shown by the organisers of the translocation programme.

It's not going to be easy - already this year poachers have killed close to 20 rhinos in Chitwan because the Royal Nepal Army has been busy fighting the Maoist guerrilla insurgency elsewhere in the country.