It's a little before midnight, and a matte-green Land Rover pickup with its headlights off and its dashboard darkened creeps along a dirt track beside a 10-foot-high electric fence. At the wheel, driving by moonlight and keeping the engine as silent as possible, is a former Australian Special Forces sniper with years of experience with this kind of mission from having served a dozen tours in Iraq.

Three armed men dressed in camouflage stand in the flatbed, their eyes scanning the fence line and the terrain ahead for the telltale ridge of sand that has been turned by a boot, or a blade of grass slowly springing back to upright, or the faint residue of wood smoke in the still air.

All could point to an invasion.

Fresh footprints are visible from a male lion that passed this way less than an hour ago. A herd of a dozen eland antelope emerge from the bush to the left. Ahead, a startled spring hare bolts for its burrow.

Farther on, something else catches the driver's attention. He stops and unfolds his mountain of a frame from the truck's cramped cabin and raises a night-vision scope to his eye, an infrared light in his hand. He scans the valley below while the other men fan out around the vehicle, establishing a perimeter.

Two electric lights flicker in the far distance. They would be invisible without the extra gear, equipment more apt to be found on a battlefield than here in a Zimbabwean game reserve a short drive from Victoria Falls. The driver, Damien Mander, a no-nonsense Australian who is a former elite soldier and gun for hire, quietly calls over his colleague, Chelepele Phiri, a mild, composed Zimbabwean with a quick smile who nonetheless handles his rifle with meaningful menace. Together, they focus on the pinpricks of light a mile away.

"Inside the reserve, or outside?" Mr. Mander whispers to Mr. Phiri.

"Outside. But close to the fence," the ranger replies.

The interlopers these men are looking for are poachers. Inhabiting the 12,000-acre reserve are a handful of endangered black rhinos as well as a sizable number of elephants, lions, and leopards. They are a trove for desperate men paid by rich people to come to kill and to carry out treasures whose value far away across oceans is rising higher than ever.

The illegal trade in wildlife and its horns, tusks, skins, and body parts has never been more lucrative. Its raw materials have never fetched higher prices, and the lengths to which people will go and the risks they will take to supply expanding markets in Asia have never been greater.

It is an industry now worth close to $20 billion a year, ranking it fourth behind drugs, weapons, and human trafficking as a global criminal activity. President Obama says its proceeds fund terrorism. The issue is serious enough that 50 world leaders gathered in London in mid-February at the invitation of the British Prime Minister and Prince Charles and Prince William for the highest-level summit on poaching in a generation.

On the eve of the gathering, Mr. Obama announced a new "national strategy for combating wildlife trafficking." It is designed to boost law enforcement efforts, reduce demand for illicit products, and strengthen partnerships among those fighting poachers.

But to people like Mander, founder and chief executive officer of the International Anti-Poaching Foundation (IAPF) – registered in Houston, headquartered in Zimbabwe, and training rangers across Southern Africa – the way the world is fighting back against this sophisticated new enemy is failing. What's needed, according to this military man, and to growing numbers siding with him in an acrimonious debate among conservationists, is total war on the poachers. Mander's philosophy, at its core, is simple: You don't want to show up at a gunfight armed only with good intentions.

"Look, I get it that we need to win the hearts and minds of the people living around here so they turn against the poachers," he says, sotto voce, leaning against the Land Rover while still looking through the night scope. "Hearts and minds: It rolls off the tongue so easily, but when has it really worked, shifting an entire population to your side? It didn't work in Iraq against the insurgency. It didn't work in Afghanistan against the Taliban. And it's not yet working in Africa against poachers.

"Meantime," he adds, "while we're trying to win people [over], tens of thousands of animals are being killed every year. We need to do something now, on the ground, to stop the hemorrhaging. Otherwise there won't be anything left by the time we've won all the hearts and minds."

Mander's urgency is not misplaced. Poachers in South Africa killed the equivalent of one rhino every eight hours in 2013. They hacked or sawed off their horns and sold them on the world market for as much as $27,000 per pound – more than the price of gold. That makes the average horn on the average rhino worth close to a quarter-million dollars.

Across Africa, the number of elephants has fallen from 1.3 million 40 years ago to fewer than 400,000 today. Each year, the continent loses somewhere between 5 and 10 percent of those that remain. This has prompted organizations such as the Convention on International Trade in Endangered Species to predict that Africa will lose a fifth of its elephants in 10 years.

Other groups warn that the African elephant could be extinct within a generation, consigned to picture books, zoos, and eventually fairy tales, like the unicorn.

Mass killings of Africa's wildlife have happened before, notably in the 1970s and '80s, a period known as the "ivory holocaust." In 1989, an international ban on trade in elephant ivory curtailed the supply of illicit animal parts, and populations of the hardest-hit wildlife began creeping up again.

But so did the demand. Asia's growing middle class increasingly sought out the animal contraband that serves both as ancestral trappings of wealth and a source of traditional medicines.

To supply these expanding markets, poaching has surged again. But this time the sophistication, funding, and malevolence of the poachers and their big-time criminal underwriters have reached new heights.

The few who are caught are often found with their own night-vision goggles, sniper rifles, bandoliers of ammunition, and other specialized gear. Big-money backers equip the gunmen with helicopters to land inside the electric fences that guard wildlife. They bribe veterinarians to supply the poachers with powerful animal tranquilizers, which are used to fell the beasts all the more quickly.

In the face of this onslaught, the world's conservation organizations have significantly increased their efforts despite chronic underfunding. But Mander argues that the conservation "industry," as he calls it, is "dangerously fragmented" and wasting energy pulling in different directions.

"It's a world wildlife war. Don't let anyone tell you it's anything else," he says back at his main encampment in Zimbabwe. "And the way we're heading, we're going to lose."

• • •

Mander is an unlikely poster boy for an environmental conservation movement. Born in the late 1970s and raised in a beachfront suburb of Sydney, Australia, a "teenage hothead full of testosterone," he admits he had "no concern whatsoever" for animals, "besides our German shepherd."

In his youth, he would make pocket money by scuba diving to find lost fishing lures and then sell them back to the fishermen who lost them. At age 19, he joined the Australian Navy and soon transferred into the force's equivalent of the US Navy SEALs. Six years later, he had become a fully trained Special Forces sniper and specialist diver. But his commission ended, and he shifted into private security and protection of VIPs in Iraq.

As he helicoptered into Baghdad in 2005, Creedence Clearwater Revival's Vietnam-era anthem "Fortunate Son" on his iPod, adventure was all that was on his mind. At the time it would have seemed crazy to him that a decade later he would be patrolling the African bush at midnight, earnestly protecting wild animals.

Twelve tours and three years later, he'd become a wealthy man but decided to quit. He'd taken fire regularly, worked with good guys and guys not so good. He'd set up a base in a former Iraqi national intelligence building, where the trappings of Saddam Hussein's autocratic rule were still visible, including the "huge date palm stumps out back where they executed detainees." He'd spent time training the Iraqi police, a job he says meant he "maybe had a positive contribution in an otherwise bad situation."

Feeling uneasy about the ethics of the war, he left Iraq and spent 2008 partying his way across South America, eventually, he says, "hitting rock bottom."

Mander returned to Australia. He recalls a barroom chat he had with someone about a man who had gone to Mozambique and was running around with a sniper rifle protecting wildlife against poachers. "I don't remember how the conversation came up, but he said it as a kind of a joke – as the ultimate boy's adventure," he says. The idea appealed to Mander's sense of derring-do, and despite knowing no one in Africa, he bought a one-way ticket to Johannesburg, South Africa, and began contacting wildlife reserves offering to help.

"I can imagine how I looked back then, a white foreigner, a Special Forces background, wanting to run around in Africa and have some fun," he says. He admits he just wanted to live in the wild for a while and post some "cool" pictures on Facebook for his buddies back home.

In Zimbabwe, a wildlife reserve manager with a team of rangers out in the bush decided that hiring Mander was worth a try. At least he thought it could do no harm. So Mander lived with the rangers for six months. Slowly, he came to the realization that here, fighting poachers amid the teak forests and grasslands of the Bushveld, his military skills coupled with his enduring quest for adventure really could have the kind of "positive contribution in a bad situation" that he had hoped for when he was training the police in Iraq.

"I had a personal transformation. I realized out there in the bush that there was something much bigger than myself, and it needed protecting," he says. "I was living out with the guys, teaching them what I knew about military tactics, and they were teaching me about the bush and how to deal with the wildlife. We might be in the African bush here but the principles are no different to the techniques of working around downtown Baghdad."

Seeing the need to teach rangers about military tactics, and using money from investments he had made during his high-paying days in Iraq, Mander set up the IAPF in 2009. To date, it has trained rangers from 10 separate wilderness areas in Zimbabwe and is expanding into Mozambique. IAPF is also leading efforts from South Africa to create an international standard for wildlife rangers around Africa and beyond.

• • •

Down one of the sandy tracks that crisscross the Stanley and Livingstone Private Game Reserve, Mander's men gather one morning for advanced tracker training. The sanctuary sits on largely flat land covered with dense, low bushes that radiate the heat back into the air.

Areas of ancient cedar forest, long ago hacked down for firewood, are starting to sprout again. Bugs the size of hummingbirds buzz past. A storm builds far away to the south, but above is only expansive blue sky.

Walking slowly forward in a line, the rangers point out footprints (laid earlier by their trainer) that are so faint as to be barely visible. One of the men, Benzine Sibanda, spots where the "poacher" had rested. The imprint of his rifle butt is clear in the dirt. Victor Mumpande, a former mechanic who's now been a ranger for 17 years, finds where the man had walked backward, trying to throw off any pursuers. Broken twigs on branches and still bleeding sap mean that he had passed this way less than 30 minutes before.

Such training sessions are part of Mander's strategy to treat the rangers as warriors, which he sees as essential to thwarting the poachers. He teaches intelligence gathering and analysis, as well as overt and covert patrolling. He shows them how to set up observation posts, how to use force properly, and how to deal with battlefield casualties.

Mander deploys the gear he used when he was in Iraq, the night scopes and the infrared lights. He's working on a new gas-driven drone that can spend five hours in the air scouring the landscape for poachers. His rangers go through physical training drills every morning. Their uniforms are new and spotless.

"People will try to package it up in a softer way – I don't know why – but antipoaching is a paramilitary operation," he says. "Law enforcement should be a ranger's No. 1 job, but it's been turned into a minor role."

Mander is not the only one militarizing ranger training. In Kenya, the British Army is helping teach similar battlefield techniques. In South Africa, former special forces soldiers are doing the same. Drones are undergoing trials in a dozen wildlife reserves across Africa.

The key ingredient in Mander's approach is a perpetual show of force, which he believes acts as a deterrent. Any poacher living near a reserve where IAPF-trained rangers patrol will likely think it's not worth the risk and go somewhere less well protected instead.

If Mander's rangers do encounter poachers, the aim is to arrest them, not cut them down in a hail of bullets. Mander is proud to say that no poacher has been shot at in anger by any ranger he's trained.

Many have been arrested, however.

The last poachers to try to breach the Stanley and Livingstone Private Game Reserve, where the IAPF has its headquarters, were arrested and eventually sentenced to stiff jail terms. That was more than three years ago.

Since then, not a single poaching incident has occurred in the reserve. Meanwhile, the number of critically endangered black rhinos that were here when Mander arrived has more than doubled, thanks to a successful breeding program. Another calf is on the way.

"I'm not saying I have all the answers – far from it," Mander says. "But I'll tell you this: What we're doing is working."

• • •

As successful as Mander has been, not all conservation groups embrace the militarization ethos. The majority, in fact, favor the more traditional approach of winning the war against the poachers – what Mander terms "hearts and minds."

This entails persuading people living alongside wildlife across Africa that the animals are worth more to those populations alive, and bringing in prodigious tourist dollars, than they are killed and exploited for their tusks or horns. In places of generational poverty, as in many communities near large populations of wildlife, that can be a hard argument to win.

"I'm proud of my job, but when I go home to my village, some people see me as the enemy," says Mike Dube, one of Mander's rangers at the reserve here. "Animals are something they [get] money from, even if just for meat. It is hard teaching people the value of protecting these animals."

Yet the softer, educational approach is working in some places. The Khama Rhino Sanctuary, a three-hour drive north of Botswana's capital, Gaborone, began with just four donated white rhinos 24 years ago. Today, it has more than 30 and has already bred and relocated another 28 rhinos to wilderness areas across Southern Africa. Not one of the animals has been poached.

Most of the 50-odd people who work at the reserve are from nearby villages. Artisans sell crafts to visitors. The money trickles down to local residents. Here, says Moremi Tjibae, the sanctuary's chief warden, the "hearts and minds" strategy has been successful.

"Our No. 1 focus has been to make local people aware that these animals are worth more alive than dead," he says. "If you poach a rhino, maybe you will benefit for today, and maybe tomorrow. If you protect it, everyone benefits – and their children and their children's children. All our schools and clinics, they are paid in part by money from tourists who come to see the animals."

Critics in the conservation community worry that militarizing the antipoaching movement raises the risk of innocent people getting caught in the crossfire. They think it sidesteps the judicial process at a time when courts are beginning to impose harsher sentences on poachers.

Max Graham, the founder and CEO of Space for Giants, a Kenya-based charity focused on saving habitats for elephants, says that educating local communities about the value of conservation, even though arduous, is "the only way logically we're going to win."

"I get very nervous when I hear about guys with military backgrounds running around the bush with weapons selling themselves as the answer to beating the poachers," says Mr. Graham.

He stresses that he has not met Mander, nor specifically come across the IAPF. He is talking instead about "mavericks" who "think shooting anyone who looks like a poacher is a way to win this thing."

"Training guys on the front line is really, really important," he says. "It's been the cornerstone of our success in Laikipia [in central Kenya], where we've managed a 60 percent reduction in the illegal killing of elephants in one year. But it is imperative that the people offering that training are properly vetted, and the standard of training offered should be the best available."

He and others believe that it is important to strengthen and clarify the laws surrounding poaching, too. Space for Giants distributes a handbook to judicial officials that lays out all the laws under which poachers can be prosecuted: trespassing, illegal possession of a firearm, threatening behavior, even driving offenses. This "holistic" approach could put a surprising number more of these guys behind bars, Graham says.

Other conservation organizations are focusing their efforts thousands of miles away, in Asia, trying to get people to stop buying the horns and tusks to begin with. WildAid, a group based in San Francisco, enlists Hollywood actors, British royals, Chinese Olympic stars, and other celebrities to spread the message that buying banned wildlife products is simply not cool. Peter Knights, the group's executive director, is exasperated that so much money goes into trying to curb the poachers.

"We need to shift focus a bit towards cutting the demand," he says. "Then there's no need for supply."

• • •

Mander understands all this. He's emphatic that he does not oppose the other antipoaching approaches, even those less aggressive than his. He concedes that international donors who fund conservation charities often shy away from sponsoring the more paramilitary outfits like IAPF, indicating that the get-tough argument has yet to be won.

But all this talk about the right way and the wrong way frustrates him. It points to a sharp divide in the conservation community at a time when he believes the most urgent need is unity. To his mind, the field is overloaded with emotion and flawed logic. He cautiously backs the idea of a licensed trade in rhino horn, for example.

"I don't like it, mate, I'm a vegan after all, but we need to be logical about this: Harvesting horn could save the species." With proper regulation – a major hurdle, Mander admits – he argues there's no reason why selling limited amounts of horn taken from animals that have died naturally and from existing stockpiles couldn't help satisfy the demand in Asia and raise money to protect remaining animals.

He rails against those who "get fueled up on Facebook petitions against hunting or Asians buying rhino horn or one-off sales to help countries pay for conservation."

"A lot of people jump up and down and point fingers at Asians, saying they're bad, they're evil, taking all the wildlife, when it was actually white Europeans and Americans who came out here and shot these animals," he says. "I think it's a little misleading that we spent a hundred years killing as many of these animals as we could find, and now we are putting them behind fences and saying to everyone that we have to protect them."

Ultimately, he thinks the only way to stop poaching is to face up to a more fundamental problem: population growth. "My argument is that Africa's population is going to double to 2 billion between now and 2040," he says. "How do you convince a continent that has a common mind-set of immediacy, often born of poverty, that the long-term preservation of wildlife is more important than food on the table tonight?"

• • •

Mander and his rangers are out on foot patrol as the sun starts to dip toward the horizon and the afternoon begins to lose its heat. At first, the only noise is the swish of khaki pants through tall grass and the creak of well-polished boot leather. Then, suddenly, a bird chirps. It's a Grey Louie, informally known as the "go-away bird." It's the official lookout of the African bush, and its chatter signals something is amiss.

Phiri, the head ranger, brings the men, who are walking single file, to an abrupt halt. At first there is only dense bush. But then there is the flick of an ear, the shift of a gray-brown shoulder, a step or two of fire-hydrant legs. This is Shungu, the reserve's dominant male black rhino, one of only 5,000 left in the world.

"The rhino to me represents Mother Nature and what we're doing to the planet," Mander says. "You have an animal that's hardly evolved for millions of years and now all of a sudden it's being pushed to the brink of extinction not through any fault of its own evolution but just because humans want to use its horns. Are we going to be the generation that allows that to happen?"

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Mander pauses. The go-away bird is silent. The bugs have stopped their symphony. Distant thunder rumbles. The rhino watches the men, close enough to kill it, but in fact here only to protect. Then it trots into the undergrowth.

"A lot of people will argue that we need to be focused less on the military approach I'm trying here and more on community work and hearts and minds and sustainable alternatives for communities," Mander goes on. "Look, I'm all for that. Let's have people out there working on that. But while they're at it, I'm going to be here on the ground trying to stop the bleeding and hold on to what we've got left before everything's dead."