Dr Paula Kahumbu`s eyes are blazing and she is jabbing her finger at the distant African horizon. At anyone, everyone, who is responsible for the elephant slaughter engulfing this continent. "You realise that Kenya is now Africa`s primary gateway for ivory smuggled to Asia," she says. "What that tells us is that organised crime has taken root in this country. It is corrupting the entire chain, from the wildlife areas to our ports."

We are standing on the plains of the Maasai Mara, the most northern extension of the fabled Serengeti, one of Africa`s most beautiful wildlife ecosystems. Out here today there is tranquillity: wildlife going about its business, uninterrupted by the predations of modern man. As the sun begins to set behind the hills, zebras, wildebeest, giraffes and a small herd of elephants head towards the Sand river for water. Above, eagles and vultures are riding the thermals like so many kites against a cobalt-blue sky. Right now the only predators these animals need fear are the lions, hyenas and occasional leopards that are part of the ecological chain.

But this serene snapshot of the African wilderness adhering to its ancient order contrasts starkly with the blizzard of recent reports of elephant, rhino and big-cat poaching. Over the past three years, more than 100,000 elephants across the continent were killed for their ivory. South Africa, which has 80 per cent of Africa`s rhinos, is losing about three a day to poachers. Elsewhere lion, leopard and cheetah numbers are declining dramatically, and even less-endangered species such as giraffe and zebra are being hunted illegally for the shabby trade in skins and bushmeat.

A shocking study published in August by American academics states that Africa`s elephant population has reached tipping point, that poachers are now killing more elephants than are being born, and the species is heading for extinction. According to the lead author, Colorado State University`s George Wittemyer, "We are shredding the fabric of elephant society and exterminating populations across the continent."

Paula Kahumbu knows better than most that the African wilderness we are looking at - the idyllic Maasai Mara of so many tourist brochures - is under serious threat. For the past six years this vivacious Kenyan crusader has been playing a leading role in WildlifeDirect, the most creative, outspoken and politically active environmental NGO to emerge in recent years. Most African wildlife organisations - the AWF (African Wildlife Foundation), WWF (World Wide Fund for Nature) and Tusk Trust, for example - are dominated by white Western males, all with the best intentions but required by African political protocol to remain polite, relatively docile and deferential to the political leaders.

Dr Kahumbu is the opposite: confrontational, fearless and ready to tackle African politicians head on. "In this country," she says, "the conservation world is dominated by people who aren`t African Kenyans, and that has allowed the powers-that-be to look at it as a black versus white issue. So having me speaking out and enlisting Africans from all sectors has been an important change."

Her approach has exposed her to personal danger, and she admits she has received what she calls "veiled threats". "Dealing with issues that touch on organised crime, corruption and politics - and you can be sure these criminals are engaged with the political fraternity in Kenya - then that could be dangerous," Kahumbu acknowledges. "But the stakes are too high to back down now."

She is equally emphatic about what needs to be done to stem demand. The most "blindingly obvious move in the short term" is for the Chinese government to ban the domestic trade in ivory. "It would instantly reduce international demand by about 80 per cent," she says, "but at the moment the Chinese government is sending out mixed signals. It says it is trying to reduce demand by allowing organisations like WildAid to put out anti-poaching posters in subways and on the sides of buildings, but at the same time there are ivory exhibitions, they promote ivory markets and they recently started carving degree courses at Chinese universities. Everyone is terrified of upsetting China, but the situation is now urgent so there is no longer time for diplomatic niceties."

Kahumbu`s mentor is Dr Richard Leakey, the founder of WildlifeDirect and himself a militant conservationist, who 25 years ago ran the Kenya Wildlife Service (KWS), surrounded at all times by five bodyguards. Midway through his term as the country`s wildlife guardian in the early 1990s, the light aircraft he was piloting crashed to earth, and as a result he had both legs amputated below the knee. To this day there remain suspicions that this was an assassination attempt.

WildlifeDirect has accused Kenyan officials of protecting the international poaching networks. According to the United Nations Office on Drugs and Crime, Kenyan and Tanzanian ports are the main ivory gateways to the major consumer markets in China and, as Kahumbu says, "You can`t move ivory in that volume as an individual. You have to be connected to criminals, freighting companies and corrupt officials at the ports. We know they`re turning off the scanning machines."

The organisation has also been instrumental in the introduction of stringent new laws in Kenya to punish wildlife-trafficking offences, as well as increasing the penalties for possession of ivory or rhino horn from a paltry 40,000 Kenyan shillings (£279) to 20 million shillings (£139,000). These are now the most severe penalties on the continent. The country`s Chief Justice has also agreed to review the filing system for wildlife crime after WildlifeDirect found that in 70 per cent of recent cases files were missing, misplaced or simply thrown away.

WildlifeDirect has harassed the government into banning Furadan, an agricultural insecticide that in recent years has been responsible for poisoning hundreds of lions, hyenas, vultures and other animals. And Kahumbu has successfully put pressure on the Kenyan courts to halt government plans to go ahead with a Chinese-built four-lane highway through Nairobi National Park, the country`s oldest wildlife reserve.

Just as important as this brave and brazen confrontation with a corrupt, complacent establishment has been WildlifeDirect`s use of social-media platforms to engage Kahumbu`s fellow Kenyans in citizen conservation. The conventional colonial view is that black Africans are not interested in wildlife conservation. Kahumbu says WildlifeDirect`s social-media traffic "completely undermines that stereotyping". It gives voice to some 120 conservation projects that share their daily challenges through blogs, podcasts, tweeting, video diaries and the rest. As a result, donors are contributing small but significant amounts directly to the grass-roots conservationists as they never have before.

This work is also creating stark awareness of the poaching horrors that are now commonplace across the continent. When seven mountain gorillas were found brutally slaughtered in the Democratic Republic of Congo`s Virunga National Park in 2007, local villagers mourned their deaths intensely, and the rangers who discovered the bodies of these animals they had known well posted their life stories and photographs. Their moving WildlifeDirect blogs had a profound effect. According to Kahumbu, "That story went from the blog to the cover of National Geographic and raised half a million dollars for the rangers." It also led to the local guerrilla armies in this war-torn region agreeing to protect the gorillas in the future.

"What we did with the gorillas was to make people aware of the specific horrors behind the statistics," Kahumbu says. "So when a rhino was poached at Ol Pejeta, I was in discussions with the Lewa board [the local conservation body]. I insisted they come with me to see the carcase, and I uploaded pictures of the board members looking at a rhino that had had its face chopped off. That`s pretty powerful. By the time we got back to Nairobi that story was all over the news. It really affected people."

Kahumbu has a lot in common with Obama. Like the US President, she is the child of a black Kenyan father and a white Western mother, her father part of the first generation of Kikuyu to be educated in Western universities. And like Obama, she has excelled academically, acquiring a bachelor`s degree at Bristol university and her doctorate, in elephant behaviour, at Princeton. She is also a powerful orator, a lecturer at Princeton and author of the children`s book Owen & Mzee, the true story of a hippo and a tortoise that became inseparable friends.

Throughout her formative years, Leakey was a profound influence. They were near neighbours when she was a schoolgirl in Nairobi`s Karen suburb, and she remembers going to his house with her siblings - she was one of nine children - and testing him out on identifying animals they had found or seen. "He was never wrong," she says. Years later, after her mother had sent her to secretarial college "because we couldn`t afford university and that was regarded as the best career option for young women in those days", she turned to Leakey for advice and help in escaping a fate that for her was horrifying.

"I ran away from college after three months and decided I wanted to be a wildlife ranger and work for George Adamson [the conservationist, author and rehabilitator of lions]. Richard persuaded me to intern instead with some scientists, and he promised that if I did well he would find a way of getting me a scholarship to study at university."

Her early studies and fieldwork involved primates, and she wrote her masters papers on the monkeys of the Tana River Primate Reserve. But, like so many African conservationists, she became increasingly fascinated with elephants. This is a sentiment echoed by most of the wildlife people I have met over the years. There is something about elephants and elephant behaviour that sets them apart from other animal species. Perhaps it is their intense family bonds, or the fact that they mourn their dead, or that they can communicate over vast African plains. Whatever it is, elephants represent something special. For Kahumbu they are "mystical creatures. And they seem aware of us. They look us in the eye."

The turning point in her life came when, in-between degrees, as an employee of Leakey`s KWS, she was tasked with counting and measuring the ivory stockpile in the country`s vaults. This was in preparation for Leakey`s internationally televised burning of the tusks in 1989, an event that remains the boldest anti-trade statement in wildlife conservation. Kahumbu found her grisly auditing exercise heartbreaking. "We were weighing and measuring tusks from elephants no older than three or four years old. At that stage I was deciding what to do for my doctoral thesis, and I thought there would be no point in studying elephants because they were on their way to extinction. I was thinking that even back then!"

The 12 tons of tusks were assembled into what Leakey deemed "a macabre sculpture" and, in front of the world press, the country`s president, Daniel arap Moi, set it alight. This publicity stunt proved a major turning point in Kenyan conservation, helping to stem the tide of poaching ripping through east Africa in the 1980s. It also gave the young Paula Kahumbu an incentive to study the animals she loved and to begin working on her doctoral thesis, on the relationship between elephants and their habitats.

"I am at my happiest out here in the bush," she says as we head out from Cottar`s 1820 tented camp, where we are staying, on to the Maasai Mara plains. She admits this is something of a cultural anathema; for a long time her fellow Kenyans asked her why she would want to work in wildlife conservation. "They would say, "Why are you doing this? How can you go back to the bush - don`t you know that`s where we came from?" There was huge cultural discouragement. I just laugh at them." But times are changing and, as her social-media campaigns have proved, modern Africans do not suffer the same cultural cringe about the wilderness as earlier generations of post-colonial Africans.

We have now been joined by Leakey and are doing what so many safari-goers do - cruising through this sun-drenched landscape watching the wildlife from the comfort of a Toyota Land Cruiser. Only, today, the plains are somewhat lacking in fellow foreign travellers, for the terrorist bombing campaign that has plagued Kenya over the past two years has led to travel advisories from the British and American governments, and resulted in a significant fall in tourism.

The presence of tourists is a significant deterrent to poachers, and both Leakey and Kahumbu express concern about the knock-on effect of a major tourist downturn. Kahumbu says that if tourists stay away not only are there "fewer eyes in the park", but there is less money to support ranger patrols. The last time there was a crash in tourism, following the post-2007 election violence, WildlifeDirect raised $80,000 to restore patrol levels. If this international stay-away continues into 2015, it is agreed that a great deal more will be needed to plug the gap.

As we potter through the Maasai Mara at a leisurely pace, Kahumbu and her mentor argue like a well-worn married couple. Their mutual respect is palpable, and the bickering is good-humoured. But Leakey is concerned about her safety. "For the record," he says, "there are people in Kenya who would rather Paula wasn`t doing what she`s doing." He says she should have a bodyguard. She says she wouldn`t think of it. Then she concedes that rubbing up against the authorities can be dangerous and recalls a friend who, a few years ago, spoke out against the government and was arrested and treated badly. "He was so affected by the experience that he disappeared from the scene."

One of the crucial lessons Leakey has taught his pupil is the art of thinking big, acting accordingly, and so maintaining a high profile. Kahumbu has learnt how to market conservation ideas. Leakey has always had a great reputation as a peerless gatherer of donor funding for his causes, whether they be paleo institutions or conservation organisations. When he was head of the KWS in the late 1980s he managed to persuade international donors, led by the World Bank, to contribute $150 million to Kenya`s conservation efforts, at a time when the West was decidedly wary of giving money to east African governments. Even today he is tirelessly raising funds for his ambitious science institute at Turkana in the north of Kenya.

Kahumbu has a similar flair for attracting publicity and supporters for her organisation. Last year she secured Kenya`s First Lady, Margaret Kenyatta, as a patron of WildlifeDirect, and recently she managed to persuade the regional airline Safarilink to carry her hands off our elephants logos, but has failed to persuade the national airline, Kenya Airways. She has also convinced the airport authorities to carry warnings in the country`s four international airports about the criminality of, and stringent new laws attached to, possession and transportation of ivory.

This being Africa, there have, of course, been major setbacks. Much of the dramatic branding and artwork that has carried the WildlifeDirect campaigns over the past few years was a collaboration between Kahumbu and Patrick Richer, an Australian art director who was married to a Kenyan and lived in Nairobi. But Richer was murdered in an armed robbery in his home last November, and talking about her friend and his cruel demise stops her in her tracks. "We lost his genius," she says quietly, "and unfortunately all of our artwork, which was on his computer."

Outspoken and engaging though she is about everything to do with conservation, Kahumbu seems oddly diffident about her private life, though she is proud of her 21-year-old son, who is serving in the US Navy. In a recent interview for a Kenyan website she described her status as single. In fact, in May 2010, she married the journalist Peter Greste under the acacias at Nairobi National Park. He is one of three foreign correspondents recently jailed by the Egyptian authorities. When I ask her how she feels about this, she shrugs it off, saying, "We broke up in 2010." And that`s all she wants to say on the subject, though they are still married.

Two days in the Maasai Mara is all the time Kahumbu can afford, for there are meetings, emails, blogs, conference calls and publicity campaigns to attend to back in Nairobi. So the next morning we bounce along the corrugated dirt road heading for the Cottar`s camp airstrip, and I ask her whether, in the face of all the gloomy statistics we`ve been discussing, she is optimistic about the future of Kenya`s wildlife. "I`m optimistic that we`ll start pushing the dealers away from Kenya by making it difficult to operate here. And that`s a new beginning." And with a flashing smile, she boards the Cessna Caravan and is gone. "An unusual woman," Leakey says as we head back to camp.

Some weeks after our trip, I get a call in my London office from Kahumbu. She is extremely animated. She tells me that a report on Kenya`s wildlife security that was commissioned by the government cabinet secretary Judi Wakhungu has just been published. It confirms everything she and Leakey have been saying about the KWS, the supposed guardians of Kenya`s wildlife.

The report accuses KWS senior managers of incompetence, citing a breakdown in communications with wildlife NGOs and wildlife conservation experts, and the fact that 50 per cent of the organisation`s vehicles were not being deployed in the field. It also claims that the intelligence networks, fundamental to anti-poaching successes in Leakey`s heyday, had completely broken down and that staff were poorly supervised and demoralised. In short, according to Kahumbu, the KWS is not fit for purpose.

"It is worse than we thought," she says. "It`s shocking. Nepotism, corruption, mismanagement of finances and much more." She believes, however, that wildlife crime "can`t be defeated by KWS alone. The government needs to look at this as an issue of national security. It requires all law-enforcement agencies to work in a strategic, coordinated way, and we need to work with neighbouring countries. President Kenyatta has to take the lead on this.

"It`s war now. We are losing our national heritage; we are losing our elephants. It`s happening inside our national parks; rangers are being shot by other rangers because they`re poaching. We have to act now."

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