A mountain lion known as P-22 lived for years in Los Angeles' Griffith Park, trapped in just nine square miles of habitat surrounded by freeways. His isolation became a symbol of urban wildlife's struggle—and a catalyst for change. When he died in 2022, construction had already begun on a massive wildlife crossing that will prevent other animals from suffering his fate.

Cities have long been seen as the antithesis of nature. But that's changing fast. As urban areas expand to house the two-thirds of humanity expected to live in cities by 2050, a new approach is taking hold: turning concrete jungles into wildlife corridors that reconnect fragmented habitats.

The Problem: Islands of Isolation

Cities occupy less than 2% of Earth's surface but produce around 70% of the world's carbon dioxide emissions. They've also carved nature into isolated patches. Between 2001 and 2017, the United States alone lost 24 million acres of natural area—equivalent to nine Grand Canyons—largely to housing sprawl.

The consequences show up starkly in places like the UK, which has lost almost half its biodiversity since the 1970s. Roads and development create what biologists call habitat fragmentation. Animals get trapped in shrinking territories, unable to find mates or new food sources. Genetic diversity plummets. Populations collapse.

David Szymanski, Superintendent of National Park Service, puts it bluntly: "Twenty years of research shows that the biggest conservation challenge facing the wildlife of the Santa Monica Mountains is isolation by roads and development."

Building Bridges Over Highways

The solution sounds simple: give wildlife a way across. The execution is anything but.

The Wallis Annenberg Wildlife Crossing, spanning ten lanes of the 101 Freeway west of Los Angeles, is the world's largest wildlife crossing. At $92 million, it's also one of the most expensive. Construction began on Earth Day 2022, with completion expected this year.

But the price tag tells only part of the story. This crossing has been discussed for more than thirty years. Thousands of hours went into design, planning, and securing funding from the Annenberg Foundation, National Wildlife Federation, and California Department of Transportation.

The structure itself is engineered deception. Five thousand plants grown from local seeds—wildflowers, shrubs, native grasses—will cover the bridge. The goal is making it feel like natural terrain to mountain lions, bobcats, coyotes, mule deer, and dozens of other species that need to move between the Santa Monica Mountains' fragmented habitats.

Wildlife crossings aren't new. France built the first overpasses in the 1950s. What's changed is the scale and urban focus. Colorado's I-25 Greenland wildlife overpass, completed in December 2024, is now North America's largest, connecting 39,000 acres of habitat near Larkspur.

Research shows these structures work. Wildlife movement between isolated populations increases. Genetic mixing improves. Road kill decreases.

Cities That Think Like Ecosystems

Some cities are going beyond individual crossings to reimagine their entire urban fabric.

Singapore maintains more than ninety miles of "Nature Ways"—canopied corridors that connect green spaces throughout the city. These aren't just parks strung together. They're deliberately designed pathways that let wildlife move safely through one of the world's most densely populated places.

The results surprised even the designers. At Bishan-Ang Mo Kio Park, biodiversity increased by 30% within just two years of rewilding—without introducing a single animal. Create the habitat, and nature shows up.

Singapore's Gardens by the Bay takes the concept further. Eighteen "Supertrees," some reaching 160 feet high, house over 158,000 plants. These vertical gardens clean air, provide habitat, and demonstrate what's possible when cities treat nature as infrastructure rather than decoration. Singapore is now considered Asia's greenest city.

London took a different approach in 2019 when Mayor Sadiq Khan declared it the world's first National Park City. The designation isn't just symbolic. It represents a commitment to making the entire city wilder, greener, and healthier for both humans and wildlife.

Gardens already cover about a quarter of London. The strategy is turning these private spaces into a connected network—habitat corridors that link to larger green spaces. When thousands of gardens connect, even small urban lots become part of something bigger.

New Delhi operates six biodiversity parks totaling nearly 2,000 acres. Nottingham is planning to convert a shopping center site into six acres of urban wetlands, woodlands, and wildflowers that will link the city to nearby Sherwood Forest.

The Science of Urban Nature

The benefits go well beyond helping wildlife.

Cities create "urban heat island" effects, running several degrees hotter than surrounding countryside. All that concrete and asphalt absorbs and radiates heat. Green spaces counter this. They cool through evapotranspiration and shade.

The mental health benefits are measurable. Green spaces lift mood, reduce loneliness, stress, and anger. They help treat anxiety and depression. Physical health improves too: lower blood pressure, better immune function, even reduced eyesight problems.

During COVID-19 lockdowns, wildlife rapidly returned to cities. Hippos appeared at gas stations in Saint Lucia. Pumas walked Chilean streets. Wild boars explored Italian towns. Goats took over Welsh streets. The speed of nature's return demonstrated something crucial: it's not that wildlife can't live near us. We just haven't left room.

Microrewilding—small-scale efforts by individuals and communities—can reduce flood risk, improve air quality, and counter heat islands. A rain garden in a front yard. Native plants instead of lawn. Leaving leaf litter for insects. These small acts accumulate.

The Public Wants This

Eighty-one percent of Britons support rewilding, according to a Rewilding Britain poll. Only 5% oppose it. That's remarkable consensus in polarized times.

Part of the appeal is accessibility. Research shows that 96.7% of cities are within a two-hour journey to biodiversity-rich recreational areas. But that access isn't evenly distributed. Lower-income neighborhoods typically have less green space, creating environmental justice issues that rewilding can help address.

What Comes Next

Urban rewilding represents a fundamental shift in how we think about cities. For centuries, urban planning meant controlling nature, pushing it out, paving it over. The new approach treats cities as ecosystems that can support both human and non-human life.

The challenges are real. Wildlife crossings are expensive. Rewilding requires long-term commitment. Not everyone wants coyotes in their neighborhood or native plants instead of manicured lawns.

But the momentum is building. As the Wallis Annenberg Wildlife Crossing nears completion, other cities are watching. The question isn't whether urban wildlife corridors work—decades of research confirm they do. The question is how fast we can build them.

P-22, the mountain lion who spent his life trapped in Griffith Park, won't benefit from these changes. But the wildlife that comes after him will inherit a different kind of city. One where concrete and nature coexist. Where highways have bridges built specifically for bobcats. Where cities function as corridors rather than barriers.

That future is already being built, one crossing at a time.