Efforts to protect biodiversity are now focusing less on preserving pristine areas and more on finding room for wildlife on the margins of human development. As urban areas keep expanding, it is increasingly the only way to allow species to survive.

One morning not long ago, in the southern Indian state of Karnataka, I traveled with a Wildlife Conservation Society biologist on a switchback route up and over the high ridge of the Western Ghats. Our itinerary loosely followed the corridor connecting Bhadra Tiger Reserve with Kudremakh National Park 30 miles to the south. In places, we passed beautiful shade coffee plantations, with an understory of coffee plants, and pepper vines — a second cash crop — twining up the trunks of the shade trees. Coffee plantations managed in this fashion, connected to surviving patches of natural forest, “provide continuous camouflage for the predators,” — especially tigers moving through by night, my guide explained, and wildlife conflict was minimal. Elsewhere, though, the corridor narrowed to a thread winding past sprawling villages, and conservationists played a double game, part handholding to help people live with large predators on their doorsteps, part legal combat to keep economic interests from nibbling into the wildlife corridor from both sides. It was a microcosm of how wildlife hangs on these days, not just in India, but almost everywhere in the world. For conservationists, protecting biodiversity has in recent years become much less about securing new protected areas in pristine habitat and more about making room for wildlife on the margins of our own urbanized existence. Conservation now often means modifying human landscapes to do double-duty as wildlife habitat — or, more accurately, to continue functioning for wildlife even as humans colonize them for their homes, highways, and farms. There is simply no place else for animals to live. The ambition to create new protected areas still persists, of course. National parks, wildlife refuges, and other protected areas remain essential, especially for species that do not adapt well to human-dominated landscapes. The 168 signatory nations to the Convention on Biological Diversity (CBD) have acknowledged as much, at least on paper, committing to extend protected area coverage to 17 percent of their land area by 2020. But getting there has proved difficult. Coverage by national parks and other terrestrial protected areas has remained stuck for the past few years at about 15 percent worldwide, well short of CBD commitments, much less E.O. Wilson’s grander vision of “half-Earth” set aside for nature.

Research has demonstrated substantial improvements in biodiversity from wildlife corridors as little as 25 yards in width.

Meanwhile, though, work to improve buffer zones around parks, and to establish corridors on the land between existing protected areas, has flourished. For instance: Just since 2000, the area protected by land trusts in the United States has more than doubled, from 23 million to 56 million acres, according to the Land Trust Alliance. Easements are one increasingly common tool for conservation on private lands, though recent research indicates that those easements tend to impose fewer restrictions on landowners than in the past.

Corridor protection on the grand scale has achieved remarkable results, notably with the 2,000-mile long Yellowstone-to-Yukon Conservation Initiative. It aims to connect protected areas and to ensure safe passage for elk, grizzly bears, and other wildlife across 500,000 square miles of largely shared habitat, both public and privately owned. At the same time, research by Nick Haddad, a conservation biologist at the University of Michigan’s W.K. Kellogg Biological Station, has demonstrated substantial improvements in biodiversity from corridors as little as 25 yards in width, well within the range, he says, of “what’s reasonable in urban landscapes.” Indeed, a new study from northern Botswana has found that elephants traveling from Chobe National Park to the nearby Chobe River will use corridors as small as 10 feet wide to traverse newly urbanized areas. Urban areas now increasingly recognize that it’s cheaper to protect clean water by buying up natural habitat both within their own borders and at the source, instead of installing expensive technology to purify it after the fact. It’s not just about New York City purchasing huge chunks of the Catskills. North Carolina’s Clean Water Management Trust Fund, for instance, has also protected 500,000 acres of watershed and riverside habitat over the past 20 years — with enormous incidental benefits for wildlife.

The 250-acre Gardens by the Bay park in Singapore. Nearly half of Singapore's land is comprised of green space and nature preserves. Martin/Flickr

Cities have begun to recognize the value of protecting wildlife within their own borders. Singapore, for instance, has increased its natural cover to almost half its land area over the past 30 years, even as its human population has doubled. Its Central Catchment Nature Reserve has become one of the last refuges of the straw-headed bulbul, a bird once common across Southeast Asia. The government also recently announced plans to create new nature parks as habitat for the critically endangered banded leaf monkey.

Even in the absence of new parks and other habitat, city residents have rallied to their wildlife, sometimes in extraordinary fashion. In Mumbai, development-oriented politicians continue to encourage the destruction of natural habitat, particularly in the Aarey Milk Colony neighborhood abutting the city’s Sanjay Gandhi National Park. But local conservationists, together with the park itself, have launched a pioneering campaign to help densely populated neighborhoods around the park cope with more than 30 free-ranging leopards in their midst. Likewise, Los Angeles has turned its mountain lions into urban folk heroes. (The Facebook bio of the lion known as P22 begins: “Hi! I’m LA’s loneliest bachelor. I like to hang out under the Hollywood sign to try and pick up cougars. Likes: Deer, catnip, Los Feliz weekends. Dislikes: Traffic, coyotes, P-45.”)

While gas and electric transmission lines commonly divide and destroy landscapes, some utility companies have found maintenance savings (and good press) by managing these corridors as habitat, especially for pollinators and migratory birds. California’s Pacific Power & Gas, with 6,400 miles of gas transmission lines, is the latest U.S. utility to sign up with the Right of Way Stewardship Council.

Highway departments have learned that they can save money, reduce their carbon footprint, please tourists, and also help wildlife by converting roadsides and medians from grass to wildflowers. The Federal Highway Administration recently published best management practices for using roadside margins as pollinator habitat — with Florida incidentally saving $1,000 per road mile in mowing costs and Oregon reducing pesticide use by more than 25 percent.

While restoration of abandoned rail lines as habitat and hiking trails is old news, British companies have recently begun restoring habitat along active rail lines. Network Rail, which controls most of the rail lines in the United Kingdom, works with conservation groups on species from the great crested newt to the natterjack toad.

The idea of making human landscapes more wildlife-friendly dates back at least to the anti-lawn movement of the 1970s.

The idea of making human-dominated landscapes more wildlife-friendly dates back at least to the 1970s, when the anti-lawn movement proselytized for turning backyards into habitat. But finding ways — large and small — for wildlife to live among us has come to seem dramatically more urgent in recent years. That may be partly because in this century Homo sapiens has become a predominately urban species for the first time in history, with huge projected growth in cities and megacities. It may also be due to a series of recent studies on the implications of that growth. These studies read, at times, as if the researchers are looking up from their data and describing the end of the natural world.

Even scientists were stunned in October by the report of a mass insect die-off in Germany. That study, published in the journal PLOS One, found that over a 27-year period, from 1989 to 2016, the population of flying insects at nature reserves across Germany had collapsed, down by 76 percent overall, and 82 percent in the peak mid-summer flying season. Most of the likely causes — including habitat fragmentation, deforestation, monoculture farming, and overuse of pesticides — were factors outside the borders of these ostensibly protected areas. “We appear to be making vast tracts of land inhospitable to most forms of life,” one co-author grimly commented, “and are currently on course for ecological Armageddon.” That came on the heels of a July report in the Proceedings of the National Academy of Sciences describing a “biological annihilation” in which “as much as 50% of the number of animal individuals that once shared Earth with us are already gone,” with likely “cascading catastrophic effects on ecosystems,” and on economic and social services “vital to sustaining civilization.” In particular, global vertebrate populations — from elephants to amphibians — declined by 58 percent from 1970 to 2012, a 2016 report noted, with losses likely to reach 67 percent by 2020. That’s two-thirds of all vertebrate animals on Earth vanished in the lifetime of a person not yet 50.

A female mountain lion in the Verdugos Mountains, north of Los Angeles. Also known as cougars, these animals are an increasingly common sight in the mountains surrounding Southern California's cities. National Park Service

In the face of “annihilation” and “Armageddon,” emphasis on tending the margins of our lives can seem, yes, marginal. “If the focus is on degraded landscapes – roadside edges, powerline rights of way – you can find examples where these habitats are important to particular species,” says Josh Tewksbury, a conservation biologist at the University of Colorado, Boulder. “But it would be hard to find any evidence that it’s going to make a whit of difference to the big problem. It’s not going to solve 95 percent of the problem.” Then, as a second thought, he added, “It could be the 95 percent solution for people and biodiversity,” in the sense that routinely seeing birds in a city park, or a fox running across a field, can have “big implications for how people think about the value of nature.” And changes in human attitudes about nature can have dramatic effects on the ability of wildlife to survive in human-dominated landscapes. For instance, persistence of old cultural attitudes is the major reason wolf recovery has struggled in the U.S., despite an abundance of available land. Meanwhile, Europe, one of the most industrialized landscapes on earth, has welcomed the return of wolves even to the fringes of its largest cities — along with brown bears, lynx, bison, and other species. The surprisingly rapid recovery of such species in Europe has led to a call, as a recent commentary in the journal Conservation Letters put it, for rewilding to become “a primary component” of long-term biodiversity conservation on degraded landscapes elsewhere — even perhaps everywhere.

One danger is these landscapes may become places where excess individuals from undisturbed habitat can survive but not increase.

But caution about the potential of our cities and suburbs as wildlife habitat is probably still a good idea. One danger is that these landscapes may become “ecological sinks” — that is, places where excess individuals from undisturbed habitat can survive, but not ultimately increase. Having straw-headed bulbuls in central Singapore does not, for instance, ensure survival of the species. Success with some more visible species may also blind us to broader but less obvious declines in other species. European rewilding, for instance, has not been rewilding for its insect population.