Underpaid, ill-equipped and outnumbered, park rangers fight a one-sided war against vicious gangs of poachers. Hundreds have been murdered in the defence of endangered wildlife, and their deaths leave their own families in jeopardy. David Smith reports from Zambia

Esnart Paundi rarely smiled for the camera. One old photo shows her wearing her ranger's camouflage fatigues and a pensive expression as she crouches beside a mound of bushmeat and three despondent poachers, one handcuffed. In another she is in a black leather jacket at her sister's home, leaning against the TV with a baby under her arm and sad eyes.

Death stalked Esnart. When her mother died young, she stepped in to help raise her siblings and become the family breadwinner. One of her five brothers and two of her three sisters are dead. Twice married and twice widowed, she was a single mother of five children.

When death came to Esnart herself at the age of 38, it was sudden, brutal and senseless. She had caught two more poachers trying to smuggle butchered wildlife to Zambia's copper belt. One was hiding a machete and, though she tried to flee, he hunted her down and smashed her skull with it. Her orphaned children are now scattered among different homes. The state has done nothing to help them.

Esnart was one of the foot soldiers in what has been called the thin green line: park rangers faced with an unprecedented onslaught from vicious, well-armed criminal gangs in Africa and around the world. In the past decade at least 1,000 have paid with their lives for defending wild animals, according to the Thin Green Line Foundation, a charitable organisation which supports rangers in their work, and their families in the case of bereavement.

"Once you are deployed on patrol, you know for certain: I am going to war," says Liywali Akakulubelwa, 47, a senior intelligence and investigations officer at the Zambia Wildlife Authority. "You accept that is the nature of the job."

Respite is unlikely. Rangers are braced for an escalation in the "wildlife wars" – the increasing militarisation of the planet's most precious and fragile game reserves. The struggle is as ferocious as any in nature, but unlikely to be seen in a David Attenborough documentary.

In India, the foundation says, rangers have been buried alive in sawing pits by illegal timber poachers. In Colombia they are killed when dealing with drug cartels, land mines and militias. But Africa is probably the bloodiest battleground. Elephants and rhino are under siege as the black-market prices of ivory and horn rocket. In the Democratic Republic of the Congo, tormented by rebel militias, 183 rangers have been killed in just one national park over the past decade. Last year alone Kenya lost six rangers, including a pregnant woman who was ambushed and shot in the face, while in Chad's Zakouma national park five rangers were mown down by automatic weapons during their morning prayers.

Running with the herd: an elephant family in the Luangwa Valley, Zambia. Photograph: Frans Lanting/Corbis

And this is no even contest. Some poachers are former army soldiers who do not hesitate to kill animals or humans, and they come with powerful backers. Rangers are often older and underpaid and lack the equipment, resources and training to defend themselves in firefights. When they make the ultimate sacrifice, there is often no government assistance for their families, who face a life of poverty and destitution.

Zambia, a landlocked country generally seen as democratic, inoffensive and rich in wildlife, has suffered much down the years. Its rhino population was annihilated and most of its elephants wiped out in 1970s and 80s. Efforts to reintroduce and conserve the animals now mean the "big five" – buffalo, elephant, leopard, lion and rhino – as they are a tourist drawcard.

In the early 1990s Esnart decided to become a park ranger to defend these crown jewels. Liywali, who trained with her for two years, recalls: "She wanted our animals to be protected so young ones could come and see elephants and buffalos. She wanted young people to see our natural resources in this country. She wanted to stop the trade in wildlife game meat. This is where death found her."

Esnart became a ranger in 1995, bringing a crucial income to an otherwise impoverished family. With her mother dead, Esnart helped her father with parenting. Her brother Mawto Paundi, 33, a taxi driver, recalls: "I remember she insisted that I go to school, but I refused. I now regret passing up the opportunity. She was ready to sponsor me."

Many former colleagues of Esnart claim she was aware of the risks of the job, but never dwelled on them. Mawto, however, says that she confided in him: "There was a time when she wanted to change career, get some money and do something else. She wanted to do something with computers so she could be in the civil service. It was because of the danger of going on patrol in the bush. She was concerned about the risks involved. It was around that time she died. Of course I was concerned as a brother, knowing the dangers of the job and what had happened to others who did it. A lot of other rangers have died. But I appreciated what she did for wildlife conservation."

By 2009 Esnart was working under William Soko, a senior ranger in Rufunsa district, about 80km from the capital, Lusaka, and earning about 1,350 kwacha (£160) per month. "She was very cheerful and obedient," Soko recalls from behind his desk in a modest office. "She was a fine lady, ever-smiling, everybody's darling."

Esnart was the only woman among Soko's 20 wildlife police officers, as rangers are formally called. "She was proud to be a pioneer. I gave her challenges, like patrolling through the escarpment. I thought she would say: 'No, I can't go' – I was shocked she went. It definitely changed my perception of women, because I know some males who are afraid to go there. I wouldn't hesitate to employ another female ranger. I still think about Esnart very much. She died a very sad death. She didn't deserve this type of death."

Esnart died on 14 September 2010 in Kabwe in Zambia's Central Province. She was on a route where poachers were known to transport bushmeat. A small, light truck approached her roadblock, executed a U-turn and sped away. Esnart, who was unarmed, and two other officers with rifles gave pursuit on foot into the bush. They found the vehicle abandoned and followed some tyre marks that led to a pile of bushmeat and two poachers, whom they arrested. One of the rangers then left to look for transport.

"One of the suspects had a panga [machete] hidden," Soko continues. "He moved like lightning. He struck the male officer on the head and knocked him unconscious. That officer has never been the same since – you can see he is not right any more."

Esnart ran but the poacher gave pursuit and rained blows on her head until she was dead. Soko was called to collect her body. "I cried," the 51-year-old admits. "It was a gruesome sight. I left with that grief in me and went to look for the suspects' house at 3am, and if I had found them, they would be have been mincemeat to bury."

But the suspects had gone and, more than two years later, are still on the run. It is thought one was Congolese and may have returned home. Soko adds: "If they are in Zambia, they will be caught. You can run for 10 or 20 years, but if you shed human blood you get caught. I can never forgive them. They have to pay."

Kick about: Annex Paundi 12, and his brother Chmunya Paundi, 7, play football with a ball of plastic bags at the home of their aunt Abigail Paundi. Photograph: Jason Larkin for the Observer

Soko took Esnart's body back to her home village, where her father, himself a former park ranger, was "understanding". The funeral brought a big crowd of mourners and there were songs, Bible readings and preaching. As is traditional, Esnart's colleagues fired their guns in salute to a fellow ranger.

But since then Esnart's family have received no financial compensation from the authorities she served. Soko, who is also chairman of the Game Rangers Association of Zambia, complains: "The government should have done a lot more because of the misery the children are subjected to. Their life simply collapses when they lose the breadwinner. She was a single mother and when she died everything went.

"I don't know what the government is thinking. What I do know is that they are silent. The Thin Green Line is the only organisation in the world to come to the aid of the children."

Rangers in Zambia, Africa and the world should not be abandoned by their governments, Soko argues. "It is a very dangerous job. Every year we have a death. It's nonstop. For as long as there are poachers, there are going to be deaths. If my daughters wanted to become rangers, I wouldn't allow them."

A short walk from Soko's office is the rudimentary house where Esnart lived, built of a reddish mudbrick, with a flimsy wooden door and a corrugated roof weighed down by rocks. It is surrounded by bare earth and dust. The faceless, unnamed poacher whose machete struck down Esnart also splintered a family. Her five children now live far apart in three separate towns in the care of various relatives.

The eldest, Anna Phiri, 17, is not so different from many teenagers: she enjoys going out and her favourite TV shows are Hannah Montana and Shake It Up. Her best subject at school is English, and she wants to be a journalist one day. "I wouldn't be a ranger because there is not enough security," she says.

Anna's father, Gawa Phiri, also a game ranger, died from meningitis in 2006. She lives with his sister, Martha Phiri, a primary school teacher, her husband Maxwell, an accountant, and their four children in eastern Lusaka. The approach road is dusty, bumpy, unpaved and fringed with rubbish. Outside the grey concrete-block house is the stench of raw sewage. Anna's bedroom has two double beds shared by four children. Dolls and teddy bears are strewn around the room. A green curtain is strung up by the window and the walls are pockmarked under a corrugated roof and naked lightbulb. A shoebox is perched on top of a wardrobe.

Barefoot and wearing a turquoise dress with white leggings, Anna rummages in a suitcase and produced a homemade photo album. It includes a picture of her mother with short hair, a blue T-shirt, light trousers and an unsmiling, careworn look. "I feel very bad when I look at it." Among her most precious possessions is a red and white dress that belonged to her mother. "It means a lot to me. I will wear it one day."

Recalling the day of her mother's funeral, Anna is tearful yet composed. "I was told by my aunt. It was very disturbing and shocking. My mother was very brave. I'm proud of her. I think about her a lot. It's very difficult now because I don't get to see my brothers and sisters often. I don't know how they are doing."

Across the city Esnart's son, George, 14, lives with his uncle, Mathews Phiri. "Mum didn't tell me much about the job," George mumbles shyly. "But I knew it was dangerous."

The long flat ROAD to Mumbwa, 135km from Lusaka, passes through a broiling marketplace selling farm produce, knock-off furniture and Manchester City football mugs. A sign for a traditional healer from Malawi promises penis enlargements and the magical return of runaway spouses. In Mumbwa is the simple house that Esnart bought but never occupied. It is now home to her siblings and three other children: the boys Annex, 12, and Chimunya, eight, and her adopted seven-year-old daughter Irene. Their father Annex, a polygamist who already had a wife when he met Esnart, died from an illness. Now the trio lives alongside her sister Abigail's two children.

There is electricity here and a digital TV and DVD player, but water must be fetched from an outside pump. Beyond a torn sheet in a doorway is the main bedroom, where foam oozes out of a split mattress, paint is cracked on the walls and a weathered mosquito net hangs limp. The family toilet is a dark pit in the ground in a ramshackle backyard shed.

Abigail, 31, is in charge of Esnart's estate and has kept her sister's ranger's uniform. "It reminds me of her because she used to wear it often," she says, sitting in a cramped, stuffy lounge with a fridge parked in the corner. "But I rarely look at it because it's painful."

She still feels bitterness towards the poachers whose actions that day continue to ripple through numerous lives. "I can't forgive them, because the impact of what they did is still being felt now. The main problem is that I'm the only sister looking after the kids, and I don't have a job. Sometimes I do piece work, but it might not suffice to look after the needs of the children. They miss their mother. I would like them all to be in one place, but I can't manage to keep all of them. They miss each other very much."

Another of Esnart's brothers, Muyeni Paundi, 22, a taxi driver, chips in: "The authorities should have done more. When the incident happened, she had no firearm and they had no handcuffs. They should also give financial support, especially for the kids. They were supposed to. Esnart's children need to be together for that brother and sister relationship."

A family friend wanders in, wearing the camouflage uniform of a wildlife police officer. Ellison Kanyembo, 47, had known Esnart since they were at training school in the 1990s. "We were tribal cousins," he recalls fondly. "She was good to me. We were like brother and sister, helping each other. She was courageous. She admired the job and was not frightened. She liked going in the field and seeing animals. She liked adventure in the wilderness. She liked cooking and she cooked fritters for me sometimes. I saw her three days before she died. It was as if she knew she was going to die. She said: 'Look after my children – this one, that one – I don't know if I'll come back.' It was like she was saying goodbye."

Matthies Kalounguna, a wildlife police officer, with his wife and children at thier home near to the Zambezi national park, Zambia. Photograph: Jason Larkin for the Observer

Kanyembo says that news of her death had a terrible impact on him: "It pained me spiritually, physically. There was that hurt in me."

Esnart's story chimes with those of many park rangers: gratitude for a job of any kind to feed and clothe numerous dependents, but low pay and the constant threat of a violent demise. In the absence of government support, her family was rescued by donations from the Thin Green Line Foundation.

What safety net, then, for other grieving spouses and children left to pick up the pieces? It is a question that corrodes the spirit of the Kalounga family back in Rufunsa where, down a bone-shaking dirt track, is a gate to the Lower Zambezi national park decorated with the skulls of buffalo, elephant and sable. Mathias Kalounga, 49, is among the rangers who patrols and camps there for unbroken stretches of 15 days. He has a wife and nine children aged from three to 22.

"I love keeping God's creation," he says. "I'm not afraid of anything. I have been shot at. We met some poachers and they started shooting and there was an exchange of fire. The poachers ran off and left their cooking equipment. I was not afraid at all."

But the danger weighs heavily upon his wife, Loyce. "It was close to the camp and we even heard the gunshots. I was worried that my husband might be killed and not make it home. He was outnumbered – three rangers against four poachers. I wish he did a different job, because this one is very dangerous. When I worry, I don't feel well."

If the worst happened to Mathias, Loyce, a housewife, would be left alone to fend for her children. "The authorities don't care about other people's lives," she muses. "We see what happens. Esnart was working for the government, but when she died the government did not look after the orphans. It's a big responsibility to feed my children and send them to school. When my husband dies, the government will do nothing to help me and my children. We will be in very big problems."

Even in life, the family endures deep hardship. Mathias and Loyce share the sole bed while their children sleep on the floor. There is no electricity or running water. Mathias earns just 1,700 kwacha (£201) per month. "It's very little, not enough to pay for the children to go to school. Some of them do and some don't."

When Zambia's vice-president, Guy Scott, was informed that Esnart's family had still not received any government support, he said that something had gone wrong and asked for her name so that it could be rectified.

One of the FIERCEST battlegrounds is also one of the world's most popular tourist destinations: South Africa, where on average a rhino is poached every 11 hours. Backed by international crime syndicates feeding a demand for horn in the Far East, poachers have been known to use helicopters, specialised silent tranquillisers, body armour, night-vision equipment and mercenaries experienced in rhino tracking.

Officials have vowed to "fight fire with fire" and deployed troops in the famed Kruger national park, where gun battles are increasingly common. Major-General Johan Jooste, who heads the joint military, police and game ranger operations, recently described the influx of poachers from Mozambique as an "insurgency" requiring a "counter- insurgency".

Wanda Mkutshulwa, managing executive of corporate services for South Africa national parks (SANParks), says: "Except for an accident between a ranger and a soldier who mistook each other for a suspected armed and aggressive poacher, there have been no fatalities of rangers in the Kruger national park related to suspected poaching in the past five years. This is something we live in fear of and, with the escalating incursions into the park and the increasing aggression of the suspects, it is only a matter of time before this happens.

"We are dealing with an enemy that has no rules and respects none, while the rangers are expected to first attempt arrest and can only shoot once they are shot at. The poachers are in control of time and place, because you never know where or when they will surface due to the size of the park – which is about half the size of Switzerland and bigger than Swaziland."

The rangers are the "forgotten victims" of the poaching war, according to Sean Willmore, an Australian-based conservationist, documentary maker and president of the International Ranger Federation. Willmore is the driving force behind the Thin Green Line Foundation, whose champions include Jane Goodall, the celebrated British primatologist. "Rangers are often outgunned, outnumbered and outresourced by illegal commercial poachers," Willmore says. "And, sadly, on a weekly basis, they are shot at, hacked to death and sometimes even tortured if they survive the bullets. I have many graphic and horrifying examples."

The foundation says it has given support to 80 widows and more than 550 orphans of rangers killed in action, but still has more than 900 widows waiting for help. Willmore adds: "With little or no compensation, many rangers' widows and children are often left destitute and below the poverty line. The children are often taken out of school with no source of income for the family. The poverty cycle for these families is set in motion. This is the thanks we give these rangers and their families for risking their lives for the animals we all care about."

For more information on the Thin Green Line Foundation, go to thingreenline.org.au