Rhinotek, Nyota, Serian and Jazz: four black rhinos that visitors to Lewa Wildlife Conservancy in northern Kenya won't be seeing again.

A gang of armed poachers struck early on December 1, shooting Rhinotek, an 11-year-old female, in the stomach. They picked off Nyota and Serian the following night. What remained of Jazz was found later that day. The following week a fifth black rhino was slaughtered and left to bleed to death, its horn set hacked out, just a mile from human habitation.

In the old days a lot of rhino horn found its way to Yemen, where it was carved into grotesque dagger handles, but that was before the rise and rise of China and Vietnam, where a burgeoning middle class, fed on centuries of superstition and medical mumbo jumbo, believes the horn possesses the power to cure everything from cancer to hangovers. That's why today, pound for pound, rhino horn is worth more than gold. Paradoxically, these patients would do themselves just as much good chewing their own fingernails, as the horn is made of nothing more than keratin.

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Unless they are made to understand the real cost of this useless practice, both the black and the southern white rhino will be extinct within a decade. The world's rhino population has declined by 90% in 40 years. This story is partly about habitat loss but about 600 have been poached this year alone in Africa, up from just 32 in 2007. Then it looked as if the war against the poachers was being won and numbers of both species were rising.

The biggest slaughter (more than 200) has been in the gargantuan Kruger National Park in South Africa, where the most recent locations of rhinos no longer feature on information boards for safari visitors.

Yesterday, I phoned Mike Watson, CEO at Lewa, where years ago our family succumbed to the charms of a hand-reared orphaned baby rhino that took a shine to my other half's suede desert boots. Watson was in a sombre mood, after a meeting with senior Kenyan government officials, to discuss how to tackle the crisis: "We're determined to get on top of it but rhinos have died and probably more will die before we do."

If it can happen there, it can happen anywhere. Lewa is reckoned to be an African model for wildlife conservation, especially of black rhino, which have bred so successfully that a number have been translocated to reserves where they had been poached out. Lewa's rolling scrub and muddy swamp are ideal for rhino and the entire 62,000-acre site is fenced. Profits from upmarket safaris are shared with local communities to teach them the value of keeping wildlife alive. One of the most highly trained security teams in the country patrols the place constantly. People used to say: "Even the trees have guns at Lewa." But today's poachers are no longer hungry Somalis hoping to make a quick buck but heavily armed and trained Kenyan criminal gangs that are also caught up in drug dealing and human trafficking and whose profits arm militias intent on destabilising this fragile democracy.

Last week a Lewa security guard was arrested for taking bribes for information on the routes of nocturnal patrols. Desperate times call for desperate measures. Watson is seriously considering dehorning Lewa's 130 surviving rhinos, despite the possible social impact and risk to their metabolism of frequent tranquillisation (because the horns grow back). He has just taken delivery of an American turbine helicopter and is considering employing spy-in-the-sky drone aircraft. Despite the threat of revenge attacks if poachers are caught, he says his guards are ready for a showdown. If the greedy poachers represent everything wretched about man's relationship with nature, these brave men personify the selfless care shown by others. And they have some powerful allies. Hillary Clinton raised the issue in Phnom Penh earlier this year and the Duke of Cambridge, who proposed to Kate at Lewa and is a patron of the African conservation charity, the Tusk Trust, recently stressed this battle is as much about educating Asians as Africans. He is right. The poachers must not win.