'The threat to rhinos is clear,' she said. At least 95 per cent of rhinos poached are hunted for their horns, an ingredient used by traditional herbalists to treat life-threatening fevers.

While many Western conservationists dismiss the use of rhino horn for such purposes, she said: 'It is not a myth. Keratin [fibrous proteins that are the chief constituent of horn] does work but the actual use of rhino horn seems to me a status symbol. It is nothing like as effective as aspirin.' The subject of several BBC Wildlife programmes, Ms Merz, 66, is a United Nations Global 500 award winner and among the world's leading wildlife biologists.

Since she moved to Kenya in 1976, she has persuaded landowners to share their estates with rhinos, instigated their capture for a sanctuary, raised an electrified fence to protect them from poachers and made fund-raising tours in developed countries to finance her reserve at Lewa Downs, Kenya, home to 45 black and white rhinos.

But Ms Merz has learned more than the mechanics of setting up a sanctuary. She is the first person to have studied rhinos in situ for so long, discovering that they communicate by breathing and that they can be gentle and intelligent, contrary to their popular image.

She faces the bleak reality, however, that fewer than 11,000 rhinos remain in the world, including fewer than 2,500 black rhinos, 430 of them in Kenya.

The slaughter, which feeds the trade in rhino horn, began decades ago and Ms Merz remembers the ominous signs in the 1970s when she left Ghana for retirement in Kenya with her Swiss husband, Karl.

'I could see that the same events were about to take place in Kenya that I had spent 20 years helplessly watching in Ghana,' she said. 'The forests were coming down, the wild animals were vanishing and money was all that appeared to matter to most people.' By the end of the 1960s there were as many as 20,000 black rhinos left in Kenya. In the next decade 90 per cent were killed.

Today there is not much left to poach, she said. 'Basically what is left, is inside sanctuaries.' Ms Merz saves her anger for the profiteering middlemen who, she says, are counting the days till rhinos become extinct, which will transform their stashes of keratin into a gold mine. Though banned from international and national trade - China prohibited the sale of tiger and rhino parts in 1993 - rhino horn is still available illegally via a lucrative black market.

A recent survey by the wildlife trade monitor, TRAFFIC, found rhino-horn medicines offered in 13 per cent of herbal outlets in China.

If Ms Merz has her way, however, the prime substance in horn, keratin, would be harvested from other sources, such as hooves and cow horns.

Her crusade to enhance the survival prospects of rhinos was not part of her father's grand plan for his daughter in the 1950s. When he urged her to follow in his footsteps and become a barrister, she persuaded him to allow her to take a year off before embarking on her career. She promptly set sail for Ceylon, now Sri Lanka.

Ms Merz never really went back. After returning to England briefly, she headed off to the Middle East. That was followed by a trip to Ghana, where she met and married her first husband, spending the next 20 years managing a menagerie at home, working for the Ghana Game Department and travelling the African sub-continent. She fostered orphaned chimpanzees, searched for pigmy hippos and surveyed areas suitable for game reserves.

But despite her decade-long stint as honorary warden for the Ghana Game Department, Ms Merz was no match for the economic, social and political changes sweeping wildlife out of the forests and plains and into the markets. 'In Ghana I tried so hard working for the Game Department but achieved so little,' she said.

But she was not easily deterred. Soon after arriving in Kenya, she began looking for land to build a reserve for rhinos. 'Nobody was prepared to give me enough land to breed white mice let alone black rhino,' she said of private landowners who thought her scheme was mad. That is until she met the Craigs, a family who farmed 18,000 hectares beneath the northern slopes of Mount Kenya.

'I began to realise Lewa Downs could become both my home and the place where I might at last, after a lifetime of failures, realise my dreams of helping a species that was in danger of extinction,' she said.

The family agreed to her proposed sanctuary offering first 2,000 hectares, later doubling the area and eventually turning over the whole of Lewa Downs, which is now grazed by rhinos and cattle. Ms Merz's side of the bargain was to foot the bill. At the time, she knew little about rhinos and hurriedly visited reserves in India and Nepal, the home of the greater one-horned rhino, and participated in white rhino translocations in other parts of Africa.

Kenya's black rhinos were isolated in mountain lairs: to move them to the safety of the new sanctuary - protected by a 2.5-metre electric fence - teams equipped with helicopters and stun guns were needed.

'I have had rather a splendid life and did some exciting things, but I can tell you catching rhinos without hurting them beats everything,' Ms Merz said.

Her first contact with captured rhinos gave her a hint of their intelligence - she calmed by reading them Shakespeare. But it wasn't until she played the role of substitute parent to a rhino born at Lewa that she really began to understand how intuitive they were.

'I was not prepared for how intelligent she was,' she said. 'It was a while before I realised she was trying to communicate with me through her breathing.' The calf, named Samia, was smart enough to realise Ms Merz needed to be protected from aggressive male rhinos and was 'unfailingly gentle' offering her tail to pull her up when she inadvertently knocked her down or up steep slopes during their walks.

When she was weaned and returned to the wild, Samia continued to return 'home' daily, years later even bringing her calf back for Ms Merz's inspection.

Today Lewa Downs provides not only a refuge for rhinos and other threatened species such as Grevy's zebras, but jobs for 160 people, schools, a health clinic and cottage industries.

The success of the sanctuary is dependent on stringent anti-poaching measures. Seventy-eight wardens patrol inside the electrified fence while an intelligence network collects information outside the reserve. And Ms Merz has no qualms about shooting armed poachers. 'These are very ruthless people,' she said. 'They are paid mercenary troops - they are goddamn murderers.' Ms Merz is pragmatic, accepting local cultural beliefs may take a generation to change. 'It is a huge barrier,' she admits.

Helping break down that barrier is Cathay Pacific Airways pilot Paul McIntosh, who represents the Lewa Wildlife Conservancy in the Asia-Pacific region.

He is raising money through corporate sponsorship - to help pay for Lewa's US$500,000 (about HK$3.87 million) annual running costs - and initiating a rhino education campaign in Hong Kong's schools. But he has no intention of telling people their traditional beliefs are wrong.

'What I don't think they are aware of is how close to extinction some of these resources are,' he said. 'If they kill the last rhino, there will be no more rhino horn and they have then destroyed their own belief system.' Mr McIntosh is planing to start safaris from Hong Kong to Lewa in a bid to bring people closer to rhinos and other wildlife. Only then would they begin to understand what is at stake, said Ms Merz.

Lewa Wildlife Conservancy Asia Pacific Fax: 2813 5197.