Derek Gow decided to abandon conventional farming about ten years ago, not long after the curlews left. At the time, Gow, who is thickset and white of beard, had a flock of fifteen hundred breeding ewes and a hundred and twenty cows, which he kept on a three-hundred-acre farm of heavy clay close to the border between Devon and Cornwall, in southwest England. He was renting an extra field from a neighbor, and a pair of curlews had come to forage for a few days. A farm worker spotted the distinctive brown birds; they have long beaks that slope downward, like violin bows. “He didn’t even recognize what they were,” Gow told me.

Curlews are Europe’s largest wading bird. They used to be a common sight in British marshes and meadows during the summer but have all but disappeared from the south of the country, which is intensively farmed. Gow, who is fifty-six, has experimented with breeding animals since he was a teen-ager. For decades, he worked on conservation projects, mostly to restore almost-extinct British wildlife, while looking after his sheep and cows and also running an ecological consultancy. He called a friend at the Royal Society for the Protection of Birds to tell him about the curlews. “Derek, they’re in their late twenties, early thirties,” Gow remembered his friend saying. “They’re just having one final look before they die.” The curlews left a day or two later; Gow has not seen any since. “These old, old birds coming back to this landscape to see if there was any possibility of breeding, to see if there were any mates left, to see if there was any hope of life,” he recalled. The departure of the curlews caused Gow to rethink how he used his land. “That began the whole pain of bringing the farming to an end,” he said.

When I visited Gow, in August, the last of his sheep were grazing, penned on a slope, awaiting their sale at auction in the coming weeks. We drove past them in his white pickup truck. “I don’t look at the sheep anymore,” he said. “I don’t come here. I don’t want to see them.” Gow has spent the past decade building a different kind of farm, emptying his fields of routine livestock and restocking them, at much lower densities, with the ancestral inhabitants of the northern European landscape: enormous cattle, wild boar, water buffalo, Exmoor ponies, and mouflon, a type of feral sheep. A digger was arriving that afternoon to bust up drains, tear up holes, and allow Gow’s fields to flood and fill up with water in interesting ways. Gow likes the word “contusions.” Some life was beginning to return. Greylag geese had noticed that Gow’s land was more accommodating than before, and dozens swung across the sky above us. At one point, we looked up and there were two white geese among the gray—escaped farm birds flying neatly in a skein.

Much of the unwinding of the old farm has been prosaic: removing fences and gates, to allow the new animals to move freely; repurposing sheds; retiring the dogs. This winter, Gow plans to erect two large catching pens, so that his new livestock can be examined by vets and, at least in theory, remain subject to his control. “We can have hiccups and we can have things that are tricky, but we can’t have no ability to manage this. It’s like ‘Jurassic Park,’ ” Gow said, in a way that made me feel unsure that he has seen the movie.

In its way, what Gow is doing is similar to other “rewilding” projects across Britain—a term that has become faddish and covers everything from letting a few fields go to seed, for tourist purposes, to major conservation projects, such as breaching a seawall along the Lancashire coast to restore salt marsh that had been claimed for agriculture. But what is different about Gow’s farm is that he wants it to be a breeding colony, a seedbed for a denuded island. “The outreach, if we can get this right, is going to be much bigger,” he told me. Gow is a disciple of Gerald Durrell, the writer and conservationist. In 1990, when Gow was working at a country park in Scotland, he attended a summer school at Durrell’s zoo, on the island of Jersey, in the English Channel, about the captive breeding of endangered species. In the book “The Stationary Ark,” which Durrell wrote in 1976, he argued for the creation of small, specialized zoos dedicated to propagating “low-ebb species” that were vulnerable in the wild. Such “zoo banks” would be motivated by saving animal populations rather than attracting human visitors. “The whole organization would act not only as a sanctuary, but as a research station and, most important, as a training ground,” Durrell wrote.

Gow’s farm is a zoo bank. The first enclosure that we passed held a pair of common cranes, which were hunted to extinction in Britain in the seventeenth century. In the next were black storks, which have been scarcely present since the Middle Ages. I sensed only a vague outline through the vegetation. “We’re not in the least bit interested in displaying these to people,” Gow said cheerfully. Small, whitewashed farm buildings held multitudes. One workshop was stacked with cages for young water voles, the population of which has fallen by around ninety-seven per cent this century. Gow breeds around three and a half thousand of the creatures a year. No one else does this. Cages for wildcats stood on a hillside; Gow is aiming to produce forty kittens a year. If he wants to get hold of a species, he has found that there is usually someone he can call. The problem is infrastructure for reproducing the animals: tanks, cages, food, skilled staff. “We stripped these life forms from the whole island,” Gow told me. “Replacing them is going to be an industrial process and it will go on for generations.” There are limits to what Gow will undertake. He has three lynx on his farm, and he does not want to breed them because there is no realistic prospect of their being welcomed back to the land. But pretty much everything else is there to be multiplied. When people ask Gow where his animals are supposed to live—the boar, the cranes, the pine martens, the snakes—he replies: everywhere. “That has to be an ambition for all the animals that were once here,” he said. “We should start a conversation about the wolf.”

In conservation circles, Gow is known for his impatience. The work that he does, particularly around the reintroduction of formerly native species, is a slow, vexing process. The farming lobby is strong. Politicians are unreliable. Scientists like to model things. Conservation people are too polite. Gow is done with all of that. “History is full of nice, ineffectual people that create catastrophes,” he said. Britain’s departure from the European Union and the bloc’s agricultural-subsidies program has led to the biggest reform of the country’s farming sector since the Second World War. New environmental incentives, which will come into effect next year, should in theory assist Gow, but he didn’t seem terribly interested. When I visited, he had plans to invite officials from Natural England, a public conservation body, to inspect his farm in a few months’ time. “If you get a decent person who’s keen, enthusiastic, they will try to help,” Gow acknowledged. “And, if you get a rodent, they will be no fucking use to you at all.”

Alastair Driver, the director of Rewilding Britain and a former head of conservation for the Environment Agency, the national resource regulator, has known Gow since the mid-nineties. “To be honest, a lot of people have called me a maverick over the years,” Driver said. “But, you know, I’m not anything like as maverick as he is.” Gow expresses his indifference to bureaucrats and rules in an age of ecological collapse with a rare rhetorical force. He is an autodidact from Dundee, on the east coast of Scotland, and there are times when he sounds like a preacher, both of his time and others gone before. “Everything is engineered to our whim and bequest,” Gow said, of the view from his truck. During my tour, Gow quoted from a Siegfried Sassoon war poem and recalled the defeat of three Roman legions in the Battle of the Teutoburg Forest, in Germania, in 9 A.D. He spoke of returning stones to his fields, to encourage lizard populations, which would undo the labor of medieval farmers and their “poor, dribbly, poverty-stricken children.” More than once, Gow referred to the “perfect circle of death” that has devastated the populations of virtually all British wildlife which has had the temerity to encroach on farmers’ crops or to prey on their livestock. He is millenarian and can-do at the same time. “We’re probably finished as a species, anyway. We’ve done way too much damage to this earth,” Gow said, at one point. “But the only way to forge a future that is going to be different is to start to look at where we are and reconsider our position.”

He has made mistakes. In the nineteen-twenties, a pair of German brothers—Heinz and Lutz Heck, the directors of the Munich and Berlin zoos, respectively—set out to recreate the aurochs, a lost species of wild European ox. Inspired by notions of biological purity, the Heck brothers worked from cave paintings, woodcuts, and contemporaneous descriptions of aurochs, including a few lines in Julius Caesar’s account of the Gallic Wars: “In size these are somewhat smaller than elephants; in appearance, colour, and shape they are as bulls. Great is their strength and great their speed, and they spare neither man nor beast once sighted.”

One of the project’s patrons was Hermann Göring. The brothers succeeded, after a fashion. (Each used his own combination of bloodlines, which included Scottish Highland cattle and Spanish fighting bulls.) A handful of the ersatz aurochs survived the war. In 2009, Gow imported thirteen Heck cattle from Belgium. His herd grew to around twenty animals. When we pulled into a field on the corner of his farm, a group of around a dozen muscular, long-horned cattle, tan stripes down their backs, scattered sharply to the edges. “They are fantastic-looking creatures, but they are seriously bloody dangerous,” Gow said. The cattle were intended to break up the soil, bash their way through the woods, and distribute their body weights in dung across the fields. But they were also aggressive. In 2015, Gow was forced to cull his most violent animals. The herd settled down after that, and there was a time when Gow could walk safely among the Heck, but after he let them run free through his woods, a couple years ago, something changed. A wildness returned.

A tall bull eyed us across the field. The last time that Gow tried to feed the bull, he only just managed to make it back to the safety of his pickup. The herd was back up to sixteen. “They operate as a unit now,” he said. “So, when one decides to do something, everything else follows it really fast. They’ve got big horns and they are fast as Satan.” The first two Heck had been shot the previous week and the rest of the cattle would be steadily slaughtered during the fall. “I’ve tried and I have failed,” Gow said. “That’s what an end looks like. We won’t be filming it and there won’t be anything on Instagram.” I asked Gow whether losing control during a rewilding project is a form of success. “It’s a version of success,” he replied. “But my career started in farming. And I would like to think that I’m still a fairly practical person.”

Gow’s triumph has been the reintroduction of the Eurasian beaver. He parked his car by a reed-lined pond, near the base of a small valley. A family of four beavers lives in this part of his farm (three or four families and around a dozen penned beavers live on Gow’s land over all) and they had blocked a stream and rerouted the flow of water around an old levee and flood defenses, to Gow’s obvious satisfaction. “Every single one of these medieval gutters is blocked, many, many times over,” he said. British place names are strewn with beavers: Beverston, Beaverdyke, Bevercotes, Beverbrook. John Bradshaw, the judge who presided over the trial and execution of King Charles I, in January, 1649, wore a bulletproof beaver-skin hat. But the animals were killed off by the early nineteenth century. One of the last records of their existence is a bounty of two pence paid for a beaver head in Bolton Percy, near York, in 1789.

There was a sudden downpour and we sheltered under a tree. Before Gow released beavers on his farm, rainwater poured off his fields and coursed through ditches. Around us, the ponds made by the beavers shimmered but lay still. “There is pond after pond after pond,” Gow said, “with hobbies hunting over here last week, fish swimming at the top, amphibians everywhere, dragonflies everywhere. It’s a no-brainer.” He loves beavers. “They are the most amazing architects of life.”

In “Bringing Back the Beaver,” which was published last year, Gow describes his twenty-five-year—and mostly quixotic—quest to return the animal to Britain’s waterways. Although there was progress in Scotland, experiments in England went nowhere until 2014, when an amateur wildlife cameraman filmed a family of wild beavers playing on the River Otter, in Devon, about fifty miles east of Gow’s farm. Last summer, after a five-year study, which showed that beaver dams help to alleviate flooding and filter pollutants, the government gave the animals permission to stay. I asked Gow whether he knew where the escaped beavers came from, and he named an estate near Ottery St. Mary, which has kept beavers in enclosures since 2007. But he admitted that another colony found on the River Tamar probably came from his land. “A badger let them out. It was an act of God,” Gow said, insisting that there was no legal case to answer. “You are getting to a place where many people view that the system has been profoundly broken. And, if they can get the creatures, they’re going to do it. They’re not going to fill in forms.”

There are now around eight known populations of wild beavers in England. Their return delights Gow and unnerves him, too. He is sometimes known as “Beaver Man,” and landowners often call him to see if he can obtain animals for them. Gow’s farm has a quarantine facility, for imported beavers, and he has the capacity to distribute around fifty animals per year. (I watched a beaver, known as Brian, while away a few minutes of his six-month quarantine by chewing on some willow and flopping about in a steel bath.) But there is a growing resistance to their reintroduction and signs of political unease. In Scotland, farmers have been granted licenses to cull beavers that they deem a nuisance on their land. Last year, a hundred and fifteen animals—slightly more than ten per cent of the Scottish beaver population—were killed. Ill-founded rumors of the damage that beavers can cause (such as eating fish; they are herbivores) are widespread. The perfect circle of death remains. Gow senses a conflict looming in England, as well. Last month, the government proposed a “cautious approach” to reintroducing beavers, which would depend on the support of local farmers, landowners, and river users. “I think we have a bigger fight in our hands than we ever imagined possible,” Gow said. “And I don’t think any of us that began this journey—to get the animals, to bring them back to release—at least some, ever thought it would come to this. But I think that’s going to be elemental. And I think it’s going to be really brutal.”

It was time to feed the wildcats. Gow has been breeding the creatures, which are Britain’s rarest mammal, on his farm for the past three years. Their scientific name, Felis silvestris, means wood cat, just like their old English name, and they used to be common, shy inhabitants of the country’s forests. Their name and their reputation became fearsome over time. Gow carried a white bucket of dead, day-old chicks into a large cage where a family of tame wildcats, which were no larger than tabby house cats, with thicker, barred tails, hopped out of the undergrowth to snatch them off the grass.

“It’s a tiny animal, isn’t it?” he said. The cats watched Gow through the leaves as he spoke. “There’s nothing to alarm you in this. . . . They’re not going to take sheep. They’re not going to take children. They’re not going to change your social order.” Britain’s first official reintroduction of captive-bred wildcats is due to take place in the Cairngorm Mountains, in Scotland, in 2023. Gow told me about a meeting he attended where he was told that the process in England and Wales—which would involve the design of nesting boxes, scientific models, and consultations with cat-welfare groups—would take at least seven years. “Before you’ve bred one kitten, opened one door, put one radio collar on, the whole thing has been sucked of its essence by deviations and cul-de-sacs,” Gow said. “No.” He was planning to work quicker than that.