When wild animals are on the move, wildlife corridors can keep them from harm
Feature Opener

By Wendee Nicole

At the onset of the breeding season in May 2010, a two-year-old male Florida black bear called M34 began his perilous journey in search of a mate. Starting in the south-central Florida oak scrub, he crossed swamps, pine forests and palmetto thickets, all while skirting human development. He swam across the Kissimmee River, moving northward for a month—until the six-lane I-4 stopped him short. M34 ambled along the freeway for a week, presumably looking for a place to cross, then gave up, turned back and returned to the area biologists first radio-collared him.

This bear’s nearly 500-mile roundtrip made Joe Guthrie, the biologist who collared M34, take notice. He wondered how wildlife can move about and expand territories when so many humanmade barriers—from roads to fences to subdivisions—fragment the landscape. Inspired by the bear, two years later he embarked on the first Florida Wildlife Corridor Expedition, hiking, biking and canoeing 1,000 miles with three colleagues to seek out wild habitat and landcover for protection like a black bear or Florida panther would do. His goal was to demonstrate the need for securing safe passageways that connect wildlife habitat from the southern tip of the state to the Georgia and Alabama borders.

Wild animals in every state face innumerable obstacles as they move across the landscape in search of food, mates and habitat. “This is true all the more as they shift their own historical ranges because of climate change,” says Bryan Bird, Defenders’ Southwest program director. “We need to make it easier for wildlife by protecting and creating corridors that connect islands of habitat.”

A corridor can be any contiguous stretch of natural habitat or it may involve “stepping stones” that allow individuals to move back and forth without having to cross a vast expanse of human development. Corridors may also include underpasses or overpasses that allow animals to move safely across a major freeway, rather than get stuck like M34—or worse. 

“Our roadways are probably the biggest cause of habitat fragmentation,” says Ben Prater, Defenders’ Southeast program director. Prater retells a story of a female black bear with three cubs crossing a busy highway in North Carolina’s Pigeon River Gorge, where two large sections of forest are bisected by a busy freeway. The mother led her cubs over the interstate, but one got stuck, unable to pull his little body over the jersey barrier in the middle (opening photo). Traffic stopped in both directions. People in cars were quietly cheering on the little cub, who eventually tumbled over and reunited with mom. Similar scenarios don’t always end happily. “It’s heartbreaking for the animals that don’t have a lot of options to get where they need to be,” he says.

Highway overpasses and underpasses have become a proven tool to successfully connect habitat interrupted by major roads. Such passages typically include vegetation, rocks and other natural elements to make animals feel at home. In Canada’s Banff National Park, roadway fencing along the Trans-Canada Highway guides animals—including bears, beavers, bighorn sheep, lynx, moose, snakes and wolverines—toward each of 44 wildlife crossings, reducing wildlife collisions by 80 percent. Other examples include a $10 million project to build highway overpasses and underpasses in Wyoming to protect pronghorn, which has reduced wildlife collisions from 85 to 16 annually, and the more than 70 wildlife underpasses in Florida constructed specifically for panthers along with crossings for bears, smaller mammals and turtles. “Animals take to them very quickly,” says Prater. “If we provide an easier path, they’re going to use it.” Other crossings have been built or are planned in Los Angeles, Utah, Colorado and more. 

When few animals remain in a population or species, connecting natural habitat via wildlife corridors and creating highway passages is even more important to their survival. One recent study found that roadways are a major threat to the survival of at least 21 federally listed species, including the desert tortoise, Florida panther, Hawaiian goose, Houston toad, ocelot, Red Wolf and San Joaquin kit fox. 

In some cases, the loss of even one animal can be catastrophic to the gene pool. The Florida panther population hovers around 200, for example, and a male panther requires up to 200 square miles of contiguous habitat, yet the population is confined to just 5% of its historical range. For this endangered population to recover, panthers need to expand their range into former habitat in northern Florida and throughout the Southeast. But road fatalities, the panther’s largest human cause of mortality, make it difficult. Dozens are killed while crossing roads every year.

Farther west, only 60 to 80 ocelots remain in the U.S. in two disconnected populations, one on Laguna Atascosa National Wildlife Refuge in South Texas, where there are only 15 known cats, and another on private ranchlands approximately 30 miles away. The leading cause of death for ocelots in Texas is also vehicular collisions. “The Texas Department of Transportation has done an amazing job building underpasses for ocelots on lands around the wildlife refuge that allow them to move through their habitat to greatly reduce risk of collision,” says Sharon Wilcox, Defenders’ Texas representative. “But we also must address long-term plans for connectivity between populations.”

For ocelots to fully recover, the two isolated groups also need to reconnect to a third population in Mexico, 125 miles south. “We call the dream connection between the U.S. and Mexico populations the ocelot coastal corridor,” says Wilcox. But protecting lands, private and public, is not enough to guarantee ocelots will reconnect. Ocelots are habitat specialists, meaning they only reside in one type of vegetation in Texas—dense, prickly Taumalipan thornscrub. “We have to restore and reconnect the native thornscrub to create corridors ocelots are willing to use,” says Wilcox.

To that end, Defenders has filed lawsuits to stop three proposed liquid natural gas terminals that would cut the ocelot coastal corridor in half and destroy some of the last remaining thornscrub habitat between the U.S. and Mexico populations.

Then there’s the border wall. Greatly expanded under the Trump administration, the border wall has had harsh implications for people that have been well-documented in the media. Less well understood are the harms caused for wildlife. The wall acts as the ultimate barrier to any wildlife movement between the U.S. and Mexico, and it has already cut off populations of jaguar, Mexican gray wolf and other wildlife. “Where the wall is standing, it has absolutely eliminated the opportunity for intercontinental migration for borderland species,” says Wilcox. 

Defenders, the American Civil Liberties Union, the Sierra Club and others lobbied to prevent a wall segment south of Laguna Atascosa, and language prohibiting the construction of border wall at the easternmost segment of the border was included in the congressional appropriations bill that was signed in December. “This is a small victory that Defenders fought hard for, alongside our partners,” says Wilcox.

But corridors are not just used to connect wildlife populations. Other wildlife species use them to follow age-old migration routes. Thousands of animals—like bighorn sheep, bison, elk, moose, mule deer and pronghorn—use these pathways twice a year.

Animals have an uncanny ability to know when to time their migrations, whether up a mountain in the summer or into valleys in winter, says U.S. Geological Survey wildlife biologist Matt Kauffman, who is working with the Wind River Reservation, which includes Northern Shoshone and Arapaho tribes, to map migrations and learn about wildlife movements from tribal elders, especially historical bison pathways. “There’s something we call ‘surfing the green wave’ which means they’re always in the right place where the green grass is just coming up and it’s most nutritious to them,” says Kauffman. “Anything that constrains their movement—fences, roads, subdivisions, energy development—disrupts those choreographed movements that they have with the landscape.”

Pronghorn are particularly vulnerable to fences in their path. “They tend to come up to fences and pace back and forth,” says Bird. “I don’t think people understand how many hundreds of thousands of miles of fences there are in the West.”

A collaborative project with the federal government helped document a 100-mile “Path of the Pronghorn” from their summer range in Grand Teton National Park to winter range to the south in Wyoming’s Green River Valley—an annual migration followed for nearly 6,000 years. In 2008, the portion located on national forestland became the first federally designated migration corridor in the U.S. Other efforts include saving additional land along the path, a highway overpass and fence modifications.  

Protecting wildlife corridors also involves legislation and policy change. A state leader in connecting habitats, New Mexico recently passed the 2019 Wildlife Corridors Act that directs the state Game and Fish Department and state Department of Transportation to identify wildlife corridors and then create a plan to reduce animal-vehicle collisions and aid wildlife movements across the state. “Defenders worked really hard with the bill sponsors to get that passed,” says Bird. A similar federal Wildlife Corridors Act was introduced in the last Congress but did not make it to a vote. It will likely be reintroduced this year. 

Connecting habitats and preserving corridors fits in with a growing movement to protect 30% of all the world’s lands and oceans by 2030 and requires the latest science—which inevitably means planning for climate change. 

“Now we don’t just have to identify which species need corridors, where they are and what they need to connect,” says Ted Weber, Defenders’ climate adaptation policy analyst. “We also have to figure out where animals will need to migrate to adapt to a changing climate.”

For example, mountain-dwelling species like white-tailed ptarmigans may have to move upslope. Coldwater aquatic species like brook trout may become confined to headwater streams. Some places, like the Southwest, are experiencing droughts that will likely worsen. Protecting riparian areas is critical when connecting pieces of habitat. “Climate change is going to affect everything,” Weber adds.

Fortunately, some states have already proactively conserved land for wildlife. Florida—where that young, inspiring bear M34 helped bring about greater public appreciation for the need to preserve and connect greenspace—has conserved more than 10 million acres—29% of the state—by acquiring, protecting and connecting ecologically important habitats.

And the resulting connectivity is working. “Just in the last few years, Florida panthers have moved into territory north of the Caloosahatchee River where females had been absent for more than four decades,” says Elizabeth Fleming, Defenders’ senior Florida representative. “One individual has had three or four litters, something that hasn’t been documented since the early 1970s.” 

While there’s a long way to go before they reclaim their former range throughout the southeastern U.S., there’s reason for celebration—not just for these panthers, but also for Florida black bears, ocelots, pronghorn and all species across the country that stand to benefit from the growing momentum behind wildlife corridors.


The I-40 Pigeon River Gorge Wildlife Crossing Project

Defenders is collaborating with a group of 20 federal, state, tribal and nongovernmental organizations to make a deadly 28-mile stretch of I-40 that borders Great Smoky Mountains National Park safer for wildlife and people. Every year, as many as 70 bears are killed in this section of highway between Asheville and Knoxville. The vertical terrain of the gorge makes solving the problem difficult, but the coalition is collecting data to recommend the best solution.

“People come here to see bears—but no one wants to hit an animal with their vehicle,” says Defenders’ Ben Prater. “If we can provide safe passage, over generations, bear, elk, deer and other species will teach their young to use those structures, and we can keep the animals out of the road.”

Learn more at SmokiesSafePassage.org.


Salmon Need Connectivity, Too

Many people don’t consider the lack of habitat connectivity in streams and rivers. In some cases, dams block the pathways of migratory fish, such as salmon in the Northwest, where Defenders is actively working to remove four dams on the lower Snake River.

The dams violate the treaty rights of the Nez Perce (Nimiipuu) tribe by physically blocking adult and juvenile salmon, greatly reducing their runs. Dams also cause the river water above the reservoirs to warm up, which harms this cold-water species, an important food source for the severely imperiled orca population in the Salish Sea. “When you look at connectivity from a salmon perspective, it’s not just impeding their movement, but it also exposes them to a whole host of risks all along the way and severely limits their ability to breed and create a new generation,” says Robb Krehbiel, Defenders’ Northwest representative.


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