Sboniso Blessing Zwane, a wildlife biology research assistant, drives me along bumpy dirt trails through the rugged hills of Hluhluwe-iMfolozi Park in South Africa. Rhino mothers and their calves graze alongside zebras; wildebeests, elephants and giraffes mingle on the grasslands; and grizzled Cape buffaloes block the trail, glaring at us before ambling off in their own sweet time. The park, in the KwaZulu-Natal province of South Africa, was once the heartland of the Zulu kingdom and has some of the greatest concentrations of wildlife in Africa. But we pass the animals here with barely a glance. We're on the trail of one of the continent's most endangered carnivores—the wild dog.

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Members of the canid family, which includes jackals, wolves and domestic dogs, the wild dog is a distinct species, Lycaon pictus, or "painted wolf." Wild dogs once roamed most of sub-Saharan Africa by the hundreds of thousands, but today there are fewer than 5,000. They're victims of habitat loss, which has both reduced their food supply and put them increasingly at odds with lions and hyenas, their natural enemies. Moreover, people have long slaughtered wild dogs, partly because the animals have been known to attack livestock but also, apparently, because of their fearsome reputation; they kill prey with such bloody ruthlessness that some farmers, I'm told, still refer to the animal as "the Devil's dog." Today wild dogs inhabit less than 50 protected national parks and private game reserves in southern and eastern Africa, where the roughly three million-year-old species is making what amounts to a last stand.

"Wild dogs are much better hunters than even lions and leopards," says Zwane, a Zulu who assists on a wild dog research project run by the Smithsonian Institution's National Zoo, as we bounce along in Hluhluwe-iMfolozi's late afternoon sun. "Once they target prey, it rarely escapes." The claim is arguable—cheetahs, lions, leopards and hyenas are also superb hunters—but, as if to prove Zwane right, a herd of about 30 impala, led by a big buck, dashes past us heading for thick bush, their eyes wide. He beams. Moments later, two of the most extraordinary creatures I have ever seen run by in pursuit of the impalas. They resemble wiry, muscular dogs, but have long, slender, supermodel legs; broad heads and massive jaws; bushy white-tipped tails; and comical Mickey Mouse-shaped ears. Their sinuous bodies are splashed with dark brown, gold, white and black splotches, like camouflage suits.

The wild dogs seem to be merely loping along, even as they match the impalas' blazing speed. We drive behind along the trail, occasionally glimpsing the impalas and the wild dogs through the scrub. A few minutes later we hear a squeal from the bushes, and then silence.

They are ruthless killers, it is true. Depending on the terrain, they can be twice as successful as lions, getting up to three out of four of the prey they target. And though wild dogs weigh just 50 to 70 pounds, their prey averages 110 pounds and, in the case of a kudu bull (a type of antelope), can weigh up to 500 pounds. Living in groups of 2 to 30 animals, with home territories as large as 770 square miles, wild dogs hunt in packs, adapting their tactics to the environment.

In the Serengeti, says Micaela Szykman Gunther, a behavioral ecologist at Humboldt State University, in California, "a pack chases a prey for a long time across the open savanna, with dogs that tire falling back and their places taken by other dogs. They exhaust the prey." But in the thick bushland of Hluhluwe-iMfolozi, wild dogs tend to catch their prey by surprise. "I once saw a pack of 17 wild dogs flush out a big male nyala [an antelope] onto the road and surround him," Gunther recalls. "They kept darting in, tiring him as he tried to spear them with his horns. They pulled him down and tore into him in seconds." Wild dogs have been known to even disembowel prey while it is still on the run.

It's that sort of behavior that has earned them such enmity. In 1914, British big game hunter R.C.F. Maugham wrote: "Let us consider for a moment that abomination—that blot upon the many interesting wild things—the murderous Wild Dog. It will be an excellent day for African game and its preservation when means can be devised for its complete extermination."

Gunther bristles at the sentiment. "Somehow, the way a big cat like a lion or leopard usually kills—by strangulation that can take many minutes—was seen as more noble than the wild dogs' swift but gruesome kill," she says. "Which is more cruel?"

Greg Rasmussen says he dislikes the term "wild dog" because it reinforces the animal's nasty reputation. He prefers "painted dog," and indeed, among canid experts, Rasmussen is "Mr. Painted Dog." His base is at Zimbabwe's Hwange National Park, in northern Matabeleland, about 120 miles from spectacular Victoria Falls. Hwange spreads across 5,650 square miles, 90 percent of it Kalahari sand. At the northeastern edge of the park, a huddle of bungalows houses Painted Dog Conservation (PDC), a program set up by Rasmussen in 2002. There are about 150 wild dogs in the park, and Rasmussen has studied them in their natural habitat for two decades.

At the center, I settle into a chalet-style room with a view of a water hole, a draw for wild animals because of a persistent drought. More than 100 elephants troop in to slurp up water and spray themselves with cooling mud just a few yards from where I sit in the darkness. A leopard slinks across the flat dry pan toward the hole, causing several sable antelope, led by a male with huge curving horns, to skitter away. But I see no wild dogs. They get much of their fluids from the blood of prey.

Rasmussen, stocky and 50 years old, was born in London and came to Zimbabwe (then Rhodesia) with his mother and father, a schoolteacher at a private academy, when he was 11. "I loved animals and found myself in heaven," he says. In 1988, an American wild dog researcher, Joshua Ginsberg, offered him a job observing the animals in Hwange National Park because, Ginsberg recalls, Rasmussen "obviously enjoyed being out in the bush for months at a time observing wild animals, and I needed someone like that to follow the wild dogs."

Rasmussen started to live with a pack, following the wild dogs around the national park in his SUV and sleeping near them. "Their hunts usually start when the temperature is cool," he says. "By 9 a.m., it's too hot to hunt, and so the dogs lie up all day, sleeping together in a great heap." Often they hunt by the light of the moon. "They're very successful in the moonlight, and get more kudu than other prey on these hunts."

What attracted Rasmussen to the wild dogs and kept him going through the lonely days and nights out in the bush was what he calls their "perfect social harmony." They rarely fight among themselves, Rasmussen says, and "the pack members daily reinforce their bonding by elaborate greeting rituals, with leaps, tail wagging, squeals, twittering and face licking—when they wake up, just before they hunt and when they come back from a kill." As Gunther says, "The wild dog is one of the most intensely social animals we know. The pack is always living, playing, walking, running, hunting and feeding together."

Rasmussen remembers once seeing a wild dog get swatted by a lion, opening a deep gash around its neck. The wound was so bad that a veterinarian Rasmussen consulted recommended putting the animal down. "The pack knew better than the vet," Rasmussen says with a smile. "The dogs dragged their wounded member away and looked after it for three months. They appointed one of the dogs I called Circus to act like a medic, constantly licking the wound and making sure the injured dog got food after the pack returned from a kill. Three months later I saw the injured dog, its neck now healed, back in the pack and taking part in the hunt." Later, Rasmussen observed a dog he called Doc seemingly deputized to be the pack's medic. Doc fed and tended five injured dogs, Rasmussen says, feeding them by regurgitating food, something wild dogs can do at will.

Rasmussen found that the animals' social organization is so complete that each pack member was allotted a task suited to its skills. A dog he named Magellan proved almost useless in the hunt, and was once seen running after a rabbit while the other wild dogs tore after a kudu. But Magellan soon took on another role—babysitter. "He stood guard over the pups while the others were away at a hunt," Rasmussen says, "alerting them of any danger so they could quickly shoot down into the protection of the den."

Wild dog litters can number up to 20 pups—one of the largest litters of carnivores—and the pups stay in and around their underground den for about three months before they begin to run with the pack. Usually only the dominant pair of dogs in each pack breeds, the alpha male and alpha female, and they mate for life. (Beta females sometimes also have pups.) "The other dogs are incredibly loyal to the puppies and join in to raise them," says Rasmussen. Unlike lions and hyenas, they allow their young to feed first after a kill, even before the dominant pair.

Because the animals are hard to track, moving up to 20 miles a day, Rasmussen began following them in an ultralight. One morning two years ago, he took off at sunrise and was not long in the air before the right wing dipped, the tail lifted and the plane plunged to the rocks. With his legs badly smashed, Rasmussen dragged himself to a nearby thorn tree. A pair of vultures circled and landed nearby. (He cheered up a bit when they flew away.) He dragged himself back under the wrecked fuselage for protection from the boiling sun. "At sunset my heart sunk, knowing there was no chance of being rescued at least until the next day." At night his throat tightened when he heard a soft "ooogh, ooogh"—a lioness calling to a lion. He banged hard on the windshield and started whacking an aluminum strut, frightening the animals away. He scared off a prowling hyena the same way.

Another day passed without food and water. The end was near, he thought, and as he reviewed his life he concluded that the most rewarding moments had been among the wild dogs in the bush. Then he heard the drone of a plane. Its pilot noticed bits of wreckage that Rasmussen had distributed near the crash site, and sent their coordinates to a helicopter, which found him and bore him to a hospital. "Above the waist I was fine," he says, "but my pelvis had a fracture, both femurs were broken, both lower legs were broken in several places, and my ankles were damaged." Several major operations put life back into his shattered legs, now shortened two inches and as stiff as boards.

Rasmussen now runs two anti-poaching patrols manned by 17 trackers who scour the area near his headquarters in Hwange National Park. In the five years since the patrols began, the trackers have found and destroyed more than 10,000 snares, circles of wire designed to trap antelope but capable of killing or maiming wild dogs and even zebra and giraffes. He has also opened a 70-acre rehabilitation facility, which currently houses five orphaned dogs behind electrified fences. So far, Rasmussen has reintroduced four such orphaned dogs into the wild. He moved them first to Starvation Island in Lake Kariba, 300 miles to the north. (Despite its name, the island is well stocked with antelope.) For a month Rasmussen provided carcasses for the dogs. "Then, they chased and killed a female kudu," he says. "They got a taste for the hunt and had no trouble getting prey after that." Once they were ready to live on their own, Rasmussen transferred the dogs to the mainland, where they have had to contend with lions and hyenas. It's too early to tell whether reintroduction will have a big impact on wild dog populations. But, says Rasmussen, "if it has saved dogs from one area that then survive to fight another day somewhere else, even if they may not always do as well, then it's a success."

"Wild dogs are the hardest of all the African carnivores to reintroduce because they are highly social and require enormous areas to roam, preferably in protected reserves," says Ginsberg, Rasmussen's former mentor, who is now affiliated with the Bronx Zoo and is co-author of the World Conservation Union's (IUCN) African Wild Dog Status Survey and Conservation Action Plan.

Of all Rasmussen's efforts on behalf of this oft-maligned beast, it seems he's most proud of the Inganyana Children's Bush Camp, "inganyana" being the local Sindebele name for wild dogs. Some 900 sixth graders each year, 50 at a time, spend four days and three nights at the rehabilitation facility, watching the dogs and learning that they are an important part of the ecosystem, helping hold other animal populations in check. They also learn that, contrary to legend, wild dogs do not normally attack people. "The kids go back to their villages and report to the chief anyone they suspect is poaching painted dogs," Rasmussen says. "Convince the local kids that they should respect painted dogs, and the battle to save them is half won."

There are signs that wild dogs are capable of making a comeback. More than 15 field projects across Africa's lower half are monitoring wild dog packs for the IUCN's Canid Specialist Group, says Claudio Sillero, who chairs the effort. And he says that although wild dogs are declining in some regions, they are becoming more numerous in others, and have even returned to the Serengeti, from which they had disappeared more than a decade ago. At Hluhluwe-iMfolozi Park, in South Africa, researchers affiliated with the Smithsonian's National Zoo say there are almost 65 wild dogs in eight packs, up from 34 dogs in four breeding packs in 2003.

Whatever the species' long-term prospects, researchers don't expect wild dog populations to rebound overnight, given what's being learned about the animals' complex social life. In most wild dog packs, all the males are related, as are all the females—but not to any of the males. When females are about 2 years old, they leave their home group and roam, looking for a group of brothers that have split off from their natal pack. "It can take months" for groups of young males and females to find each other, says Penny Spiering, a conservation biologist who directs the fieldwork for the National Zoo's project.

One glimmering dawn, Spiering and I drive along a road inside Hluhluwe-iMfolozi Park searching for wild dogs. She jams on the brakes and points ahead—there's one, in silhouette, pacing the road. She aims her binoculars and smiles. "It's Khanda, one of the dispersers. I haven't seen her in two months." Khanda is apparently searching for a new pack. Being somewhat familiar with the researchers' trucks, she trots up to us and stands by my door for a few moments. I admire her lean powerful body and keen intelligent stare. Then, with a turn of her handsome head and a flash of gleaming teeth, she trots off, vanishing in the undergrowth.

Paul Raffaele's story on the Korubo people of the Amazon was selected for 2006's Best American Science and Nature Writing.