William Bradford, looking out at Plymouth from the Mayflower in 1620, was struck by its potential. “This bay is an excellent place,” he later wrote, praising its “innumerable store of fowl.” By the next autumn, the new colonists had learned to harvest the “great store of wild turkeys, of which they took many.”

Soon, they took too many. By 1672, hunters in Massachusetts had “destroyed the breed, so that ‘tis very rare to meet with a wild turkie in the woods.” Turkeys held on in small, isolated patches of land that could not be profitably farmed. But by 1813, they were apparently extirpated from Connecticut; by 1842 from Vermont; and from New York in 1844.

In Massachusetts—land of the Pilgrim’s pride—one tenacious flock hid out on the aptly-named Mount Tom for a while longer. The last bird known to science was shot, stuffed, mounted, and put on display at Yale in 1847, but locals swore they heard the distinctive calls of the toms for another decade. Then the woods fell silent for a hundred years.

* * *

Americans used to assume a clear line between wilderness and civilization. Bradford called the land he saw a “hidious and desolate wilderness, full of wild beasts and wild men.” As European colonists moved inland from the coast, they called that boundary the frontier—on one side wild, untouched forest, and on the other, cleared fields, farms, and settlements.

Where the early settlers found squirrels or coyotes or deer or turkeys, they knew that they were venturing into wilderness. These wild creatures they hunted for food, and for sport. Onto the clear-cut land they brought new creatures—pigs and dogs and cows. They even brought tame turkeys, domesticated from a Mexican subspecies, taken to Europe, and then reimported across the Atlantic.

As Europeans advanced across the continent, they drove out its native species. And as these creatures dwindled and disappeared, the settlers began to regret what they had done. Some, like Teddy Roosevelt, saw the fauna of the New World as a natural resource, a treasure to be protected and cherished so that it could be harvested by future generations. Others, like John Muir, viewed the remaining patches of wilderness as sacred trusts, little patches of Eden to be preserved and enjoyed.

But both groups of conservationists drew a clear line between the pure preserves of nature, and the soiled, sullied domain of man. The conservation movement aimed to cordon off parts of the country from development, where woodland creatures could thrive and survive. Without such spaces, they warned, they would vanish altogether.

* * *

The squirrels were the first to return. In the mid-19th century, Boston, New Haven, and Philadelphia released small numbers of squirrels on to their commons, as curiosities. Hundreds came to marvel at the incongruity; imagine, a squirrel in the city! They dined at the public trough, of course; such wild creatures could hardly be expected to find their own food in an urban environment.

Those first released did not survive for long. But within a few decades, squirrels became fashionable appurtenances for upscale urban parks. Their presence, one contemporary gushed, “excites feelings of admiration akin to those awakened by the birds and the fairer forms of nature.” They remained dependent on the kindness of people, a necessarily fragile existence. But city dwellers cherished them, little avatars of the natural world dwelling peacefully in their midst.

Meanwhile, the forests of New England hit their nadir. They had once covered Massachusetts; by the mid-19th century, they accounted for less than a third of the state, a patchwork of land too hilly or marshy or rocky to farm. As agriculture exhausted the soil, new land to the west promised greater returns, and burgeoning industries offered steadier wages. Farmers abandoned the land their grandfathers had cleared, and trees sprouted up around the stone walls they left behind.

Today, more than 60 percent of Massachusetts is forestland. (Only a few thousand acres of that total are old-growth forest.) For conservationists, the return of the trees seemed a dream come true. As the population emptied off the land, returning to cities and their suburbs, it seemed possible to reestablish the frontier, to restore the woods to their pristine splendor, to again draw a line between nature and civilization.

Deer returned, and flourished in the woods. Hikers and campers came to see them on the weekends, and then returned to suburbia. Other creatures followed—some spreading on their own, some deliberately reintroduced. Soon, the forests were teeming with beaver, bobcats, and coyotes. In 1972, biologists trapped 37 wild turkeys in New York, and began releasing them into the forests of Massachusetts.

That’s when something unexpected happened.

The turkeys looked around at the forests. They provided safety and shelter, but were otherwise uninviting. Food was scarce; the undergrowth was dense. But adjacent to the forests was abundant open cropland, where farmers thoughtfully spread manure, there for the taking. By the time researchers arrived to study the birds a decade later, the turkeys were spending almost two-thirds of their diurnal feeding time on the cropland. The turkeys that figured out how to thrive in tandem with human activity were dramatically more likely to survive tough winters than those who stuck to the woods.

Slowly, they migrated eastward across the state, adapting at every stage to new environments. They learned to forage in the exurbs. To find seeds and grubs in the suburbs. And finally, to thrive in cities like Boston. In some places, they are now so abundant and aggressive that they have become public nuisances.

In 2013, police in the affluent Boston suburb of Brookline euthanized a turkey that was terrorizing school children. “It requires the efforts of the entire neighborhood to help keep wild turkeys wild,” police warned residents. But even an entire neighborhood working together cannot reimpose the faltering boundary between wilderness and civilization.

* * *

When Bradford looked at the coast and saw only desolation, it was because he did not understand what he was seeing. Far from an unspoilt wilderness, it was, in fact, a carefully tended landscape, cultivated by a large and prosperous population to meet its wants and needs. Native Americans set fires to clear the underbrush and provide a habitat for the animals on which they depended. They hunted the deer and the turkey which thrived in the forests they maintained.

The near-miraculous abundance of game in those early years was, itself, very likely an artifact of human intervention—a legacy of the pathogens introduced by Europeans that killed so many of the land’s inhabitants, and which may have led game populations to explode in their absence. There was no frontier dividing nature from civilization—just two different agricultural landscapes, each optimized for a different purpose.

Small wonder, then, that the returning turkeys found the woods so uninviting. Naturalists hoped to restore a pristine wilderness, but that’s not where the turkeys had once thrived. No one was burning the underbrush for them anymore, or promoting the growth of nut-bearing trees. Turkeys had lived in the New England landscape in tandem with Native Americans, who had carefully tended the environment. And once the descendants of European settlers ceased hunting them at unsustainable levels, they moved right back in.

They came back to find cities that had more space to accommodate them. Dirt lots and pavement had yielded to grassy medians and green yards. Gone were the tens of thousands of horses pulling carts, the pigs rooting through slops, and the dogs wandering off leash. They found few competitors, and fewer threats. The contemporary city might as well have been designed for turkeys.

Metropolitan Boston is again filled with squirrels, pigeons, peregrine falcons, and red-tailed hawks, as it was before the Pilgrims landed. The deer in its parks and woodlands are so abundant that they have become a nuisance, and attracted coyotes. The occasional bear or moose wanders into town. The store of fowl is so innumerable, as Bradford might have put it, that their droppings fairly pave the banks of the Charles.

And now, the turkey have come home, too. They strut proudly about town, chests puffed out with infinite complacence. The line between wilderness and civilization has dissolved. But then, it was always an illusion.