Humans are now better connected than ever before, thanks to modern conveniences like highways, jumbo jets, social media and smartphones. At the same time, though, wild animals around the world are increasingly disconnected, trapped in islands of wilderness amid a growing sea of people.

Habitat loss has become the No. 1 threat to Earth's wildlife. It's the main reason why 85 percent of all species on the IUCN Red List are endangered, and why the planet is on the brink of a mass extinction event, with species now vanishing at hundreds of times the historical background rate. This is partly due to activities like deforestation that harm ecosystems directly, but also subtler dangers like habitat fragmentation by roads, buildings or farms and degradation by pollution or climate change.

"Small fragments of habitat can only sustain small populations of plants and animals," says Nick Haddad, a biologist at North Carolina State University who has spent 20 years studying how wildlife get around. "But what distinguishes the populations living in those fragments is not just their size. It's also their ability to interact with other plants and animals of the same variety."

The earliest victims of habitat loss are often big predators whose lives rely on roaming. And once any animal's habitat starts to shrink, other risks like disease, invasive species or poaching start to grow.

"When large carnivores cannot travel to find new mates and different kinds of food, they begin to suffer genetic breakdown because they're inbreeding," says Kim Vacariu, western director for the Wildlands Network, a Seattle-based nonprofit group that focuses on habitat connectivity. "And that is the precursor to extinction. Once the genetic breakdown starts to happen, they are more susceptible to different kinds of diseases, and their life spans become much more fragile."

Thankfully, we don't have to dig up roads or relocate cities to fix this. It's surprisingly possible to co-exist with wildlife, as long as we set aside enough space to provide buffers between us. And that means not just protecting a hodgepodge of habitats; it means reconnecting them via wildlife corridors and large-scale "wildways," much like the way we build highways to link our own habitats.

Amur leopard

Reconnected habitats have helped Asia's endangered Amur leopard double total its population since 2007. (Photo: WWF-Russia/ISUNR)

Happy trails

Scientists have long assumed it's better for species to have large, unbroken habitats rather than isolated scraps, but the idea has taken a while to get mainstream attention. That's partly due to the recent speed of wildlife declines, but it's also because we finally have data to prove corridors work.

"Almost from the origin of conservation biology, corridors were recommended," Haddad says. "If you look at the natural state of habitats, they were large and expansive before people sliced and diced them, so reconnecting them made some intuitive sense. But then the question was 'do the corridors actually work?' And in the last 10 or 20 years, we've started to prove that yes, they do work."

Wildlife corridors are now in vogue. Not only have they become a key part of many governments' species-recovery plans, but they're already helping revive a menagerie of rare animals around the world, from Amur leopards and Florida panthers to giant pandas and African elephants. Corridors have become especially important in the face of high-speed climate change, since rising temperatures and other environmental changes are forcing many species to adapt by moving to cooler, higher, wetter or drier habitats — a solution that's only possible if they aren't trapped where they currently live.

In places where corridors are severed by civilization, there's a trend among conservation groups to raise awareness with long expeditions through the wildest parts of what's left. Explorers and organizers are also using digital photography and social media to share the experience with followers around the world. It's a strategy that leverages our innate love of adventure, similar to how the Appalachian Trail was created for hikers in the 1930s yet also provides 2,000 miles of habitat for wildlife. (That connectivity, along with diverse topography, is a big reason why Appalachia is now considered a climate refuge.)

FWC map

Exploratory science

The Florida Wildlife Corridor Expedition, for one, recently finished its second odyssey to highlight that state's fading ecological links. The group's inaugural 2012 trek spanned 1,000 miles in 100 days from the Everglades to the Okefenokee Swamp, inspiring widespread news coverage and a documentary film about the trip. That set the stage for the 2015 encore, which sent three explorers 900 miles from Green Swamp to Pensacola Beach, where they arrived March 19 after 70 days of hiking, biking and paddling.

"There's pretty widespread agreement that from a biodiversity standpoint, it's better to maintain the landscape in a connected way rather than letting islands form around us," says Joe Guthrie, a wildlife biologist who spoke to MNN by phone during the final leg of the 2015 expedition. "And for Florida, it's important as a framework to render a blueprint of what the state can look like, building out the state from a conservation standpoint. We've built out the state in many ways for human infrastructure, so now let's also have a vision of Florida that can function for wildlife and water as well."

Guthrie was joined in 2012 and 2015 by photographer Carlton Ward Jr. and conservationist Mallory Lykes Dimmitt, who is also the group's executive director. The journeys have captivated people in Florida and beyond, Dimmitt says, partly because they harken back to our own species' history as explorers.

"Connecting these habitats is important for the movement and genetic mixing of different populations of animals," she says. "But there's also the opportunity for recreation. I think people like the idea of being able to start out somewhere and just keep going." The Florida Wildlife Corridor is still largely intact, but only about 60 percent is protected, and as Ward notes, "roads are never far away."

Call of the wildway

North American wildwaysThe Wildlands Network has used similar adventures to promote an even more ambitious vision. Co-founder John Davis spent most of 2011 exploring the proposed Eastern Wildway, a 7,600-mile pilgrimage from Key Largo to Quebec he chronicled on his TrekEast blog. He followed that in 2013 with TrekWest, which covered the 5,200-mile Western Wildway from Mexico to Canada in eight months.

A wildlife corridor can be any size, including tiny routes used by salamanders or insects, but the Wildlands Network is focused on continent-scale pathways for large animals, especially carnivores. It has identified four major wildways throughout North America, each of which is a loose network of regional corridors it's trying to stitch together.

"A wildway incorporates hundreds of wildlife corridors," Vacariu says. "Each corridor is an entity unto itself, because they're so different. You might have one that encompasses an entire river valley, and you might have one that follows the tops of mountains. It all depends on the species you're trying to protect."

Trickle-down ecology

Carnivores are often the main focus of large-scale corridor conservation, but that isn't just for their sake. Top predators tend to be keystone species, which help keep entire ecosystems in balance.

"When large carnivores are removed from a habitat, the effect ripples through the whole food chain," Vacariu says. "Wolves were completely exterminated from Yellowstone back in the '30s, and over the next several decades their main prey, elk, exploded because it had no controlling predator above it. Elk would normally have to be wary of standing in one place and burying their heads in grass to eat, but without wolves they could become lazy and chew down all the aspen and cottonwood seedlings. And basically those trees stopped reproducing in Yellowstone due to massive overgrazing."

Wolves have since been reintroduced to Yellowstone, and they're already keeping elk in check. That has let a variety of plants flourish again, which are in turn providing perks like roots that control riverbank erosion, branches that support bird nests and berries that help bears fatten up for winter.

Conservationists hope to mimic that habitat rehab throughout the Yellowstone-to-Yukon artery, and the broader Western Wildway, as well as other carnivore-centric corridors around the world. The Jaguar Corridor Initiative aims to bridge jaguar habitats across 15 countries in Central and South America, for example, and the Terai Arc Landscape Project is working to link 11 protected areas in Nepal and India, creating a corridor for tigers as well as other rare wildlife like elephants and rhinos.

wildlife crossing

Canada's Banff National Park uses large overpasses and underpasses to help wildlife cross the TransCanada Highway. (Photo: Shutterstock)

Blurred lines

It's obviously best if wildlife can stick to wilderness, but sometimes habitat corridors need to cut through civilization. That might mean preserving a forest strip for chimpanzees between villages, planting trees for birds along the edge of a farm, or building a wildlife overpass or underpass to help elk get across a busy highway. It might even mean learning to occasionally share space with wild animals, as the Jaguar Corridor Initiative notes on its website: "A jaguar corridor is a cattle ranch, a citrus plantation, someone's backyard — a place where jaguars can pass through safely and unharmed."

For the most part, large wild animals aren't trying to commute through cities. Habitat fragmentation is often initially caused by less intensive development, like farms or ranches, and these aren't necessarily incompatible with wildlife. "Private landowners tend to freak out when their lands are identified as something that needs to be protected," Vacariu says. "So we make sure the word 'voluntary' is always included. Private landowners are asked to voluntarily manage their properties for nature conservation. And they can typically do this without changing their operations."

Conservation groups sometimes pay landowners in developing countries to protect their land or to plant trees along the fringes, a strategy that's already helping wildlife like chimps and elephants in parts of Africa. Private landowners can also sell or donate a conservation easement, which lets them keep the land — and receive tax benefits — while also permanently protecting it from future development.

bird eating insect

Preserving space for birds, bats and other predators can help farmers fight crop-killing insects without pesticides. (Photo: Shutterstock)

But preserving pockets of nature can also reward landowners directly. A 2013 study, for example, found that when coffee growers in Costa Rica leave patches of rainforest in their plantations, native birds return the favor by eating borer beetles, a coffee-bean pest that could otherwise ruin harvests. Preserving forests around farms can also support populations of foxes, owls and other predators that control rodents, as well as insect-eating bats, which save North American farmers an estimated $3.7 billion every year. Farms can blend into wilderness more easily than many other types of land use, Dimmitt notes, so it's important for conservationists to see farmers and ranchers as allies, not adversaries.

"The future viability of the wildlife corridor depends on the viability of agriculture in Florida," she says. "What typically follows agriculture is more intensive development, so the more we keep rural economies strong and the longer we keep agriculture strong, the longer those lands stay in a more natural state."

Yet despite the role agriculture can play in reuniting ecosystems, even well-managed farmland is only helpful if species have enough natural habitat on either side. Preventing a mass extinction will likely require an international surge of nature conservation in the coming decades, well beyond the roughly 14 percent of Earth's land that's currently protected. Some biologists even say we should set aside half the planet for wildlife and half for people, a concept known as "half Earth."

That's a noble goal, but its daunting scope shouldn't overshadow the incremental progress we can make in the meantime. After all, similar to a freeway system or a Facebook feed, the overall quantity of wildlife habitat isn't always as important as the quality of its connections.

Russell McLendon ( @russmclendon ) writes about humans and other wildlife.