Freedom of Movement

Biologists say that for many wildlife populations, survival depends on traveling across unobstructed landscapes

  • Tom Dickson
  • Nov 17, 2010

SOMEWHERE IN THE FROZEN, wind-whipped prairies of north-central Montana, 45 miles south of the Canadian border, a herd of pronghorn is trying to migrate south. For two years Andrew Jakes, a doctoral student in ecological design at the University of Calgary, has tracked these and other pronghorn—some moving as far as 350 miles in one year—as part of research on the animals’ migratory routes.

The pronghorn he is observing on this cold February afternoon left their Canadian summer range a few months earlier for Montana’s relatively milder winter range. Their primary route is the Milk River and its tributaries, such as one Jakes is following on a gravel county road. “Pronghorn have a very hard time walking through deep snow,” Jakes says. The animals’ tiny hooves and skinny legs punch through frozen drifts like pencils. To migrate, the prairie ungulates move along a creek’s exposed bluffs, where winds tearing across the northern Great Plains open bare areas where they can walk and find vegetation.

As Jakes’s pickup tops a rise in the road, he sees the herd of roughly 100 pronghorn feeding along the creek bluff on exposed patches of rabbitbrush and silver sage. “The way these animals deal with the harsh environment is to move,” Jakes says, as the pronghorn continue south.

A white-tailed doe can spend its entire life within a single square mile; a mole might never leave your backyard. But many wildlife species must move far and repeatedly to survive. Each summer, elk leave river valleys to graze on nutritious grasses and forbs in high mountain meadows. Young male grizzly bears seeking their own territories may travel hundreds of miles in the Greater Yellowstone Ecosystem. Male gray wolves, cougars, bobcats and other predators seek new home ranges.

During spring 2009, researchers with the Wildlife Conservation Society (WCS) tracked one young wolverine from Wyoming’s Grand Teton National Park south more than 500 miles to north-central Colorado, the first confirmed record of the species in that state since 1919. “That kind of movement shows that we still have some level of intact connectivity in this part of the Rockies,” says Steve Torbit, NWF’s executive director for the Rocky Mountain region.

Long-distance journeys are getting harder for wildlife to undertake. Roads, fences, rail lines, exurban housing and other developments increasingly chop large parcels of habitat into isolated pieces. This landscape fragmentation lessens what conservation biologists call “connectivity”—the degree to which the landscape allows animals to move from one place to another. One egregious example is the border wall being built between the United States and Mexico. Intended to slow illegal immigration, the 670-mile-long fence would also block migration of desert bighorn sheep, ocelots and other species.

Land Fragmentation

No less daunting to mobile wildlife is negotiating the growing number of homes—and accompanying driveways and access roads—popping up across rural countrysides nationwide. “Every time you put down a road, drill a gas well, erect a transmission line, whatever, it has an impact on connectivity,” Torbit says. “Wildlife can’t just move over to the other side of the mountain anymore. It’s all developed. There is no other side of the mountain anymore.”

Barriers to movement weren’t always seen as major threats to wildlife populations. Beginning in the early 1900s and continuing for much of the 20th century, conservationists focused on protecting core areas—biologically diverse habitats designated as wildlife refuges, wilderness areas and parks. Save the best habitat, the thinking went, and wildlife populations will survive. But since the 1970s, scientists have learned that protecting these habitat “islands” is insufficient. “We’ve seen more and more species declining in the robust protected core habitats, and that’s associated with increased development around those areas,” says Jodi Hilty, director of North American programs for WCS. “At the same time, we’re learning how much species need to move. So it becomes obvious the lack of movement among core areas is the problem.”

“Isolated populations suffer a variety of threats” says Kevin Crooks, associate professor of wildlife conservation at Colorado State University. “For example, isolation prevents animals from traveling to important foraging or breeding sites. It also heightens genetic risks, such as inbreeding and loss of evolutionary potential to adapt to changing environmental conditions.” Examples include floods, fires and, most ominously, global warming.

“Global warming causes habitats to change or even disappear, so that animals in the Northern Hemisphere will have to move from south to north or into higher elevations, provided that the pathways the animals need to follow aren’t blocked,” says Sterling Miller, an NWF senior scientist in Missoula, Montana. “We’re already seeing warmer weather push mountain goat and American pika habitats higher and higher into alpine areas. We’re also seeing wolverines blocked from moving between patches of the deep mountain snow they use for denning and for transportation corridors.” Says Crooks, “Few are debating the need to restore and protect landscape connectivity for wildlife. The big question is: How do you achieve it?”

Connecting Habitats

One way is with wildlife corridors. Also known as greenways, linkages and passageways, these tracts of habitat link two or more larger core areas. Some are naturally occurring, such as the creek bluffs along which Jakes’s pronghorn migrate. Others are made by humans, like the 42 culverts recently installed under stretches of U.S. Highway 93 on the Flathead Indian Reservation in western Montana to make the roadway permeable to wildlife. When reconstruction of the highway was being planned, the Confederated Salish and Kootenai Tribes expressed strong concerns about wildlife and habitat fragmentation impacts, disruption of movement corridors and vehicle-caused wildlife mortality.

A unique agreement between the tribes and state and federal transportation agencies included provisions for the crossing structures. “Initial monitoring is showing a lot of use by several species including grizzly bears, river otters, deer, elk, moose and others, as well as lower animal/vehicle collision rates in some areas,” says Dale Becker, the tribes’ Wildlife Program Manager. “The crossings are achieving our goals of maintaining habitat connectivity and movement corridors and enhancing the safety of motorists.”

In 2008, the Bridger-Teton National Forest designated a strip of land along the Gros Ventre Range in Wyoming as an official pronghorn migration corridor, the first federally designated wildlife corridor in the United States. The land is part of a 6,000-year-old migration route traveled by pronghorn that spend summer in Grand Teton National Park and winter in the Green River Basin, a round-trip of roughly 340 miles. Several landscape and development bottlenecks constrict the pronghorn’s ancient migration avenue, one to a width of just half a mile. The U.S. Fish and Wildlife Service has pledged to restrict all future activities on national forest lands within the designated corridor that would impede pronghorn movement.

That singular pronghorn route notwithstanding, one of the greatest impediments to corridor conservation is the lack of an official federal program for protecting wildlife migration routes across the nation. Hilty believes that the National Wild and Scenic Rivers System might be a workable model for adding federal weight to corridor protection. “River stretches designated under the system as wild or scenic are a mix of public and private lands, and from what we’ve seen they aren’t all that controversial. Something like that just might work for corridors.”

Protecting strips of land between core habitats can help populations remain viable, but it’s no guarantee. Some narrow greenways make prey species more vulnerable to edge-hunting predators such as coyotes, skunks, red foxes and domestic cats. In other cases, wildlife refuse to use their appointed corridors. Consequently, conservationists have broadened their scope to encompass entire ecological regions. “Wildlife don’t recognize country, state or international borders, and neither can we if we want to maintain wildlife connectivity,” Hilty says.

In the Northeast, the Algonquin to Adirondack Conservation Association works to connect a cross-border patchwork of ecological communities from southeastern Ontario to northern New York. The Two Countries, One Forest initiative conserves key wildlife linkages within the 80-million-acre Northern Appalachian/Acadian ecoregion. In southern Arizona, the 50,000-acre Cienega Corridor that links Saguaro National Park and Las Cienegas National Conservation Area facilitates movement of bobcats, jaguars and other itinerant species. The South Coast Wildlands Project is working to protect 15 critical linkages and wildlife-compatible surrounding lands in coastal Southern California one of the world’s largest metropolitan areas.

Maintaining wildlife connectivity requires not only protecting corridors but also changing human behavior and activities, says Rob Buffler, executive director of the Yellowstone to Yukon Conservation Initiative (Y2Y). With a project area of 8,000 square miles, Y2Y is the largest landscape-scale conservation effort in North America. The initiative identifies critical core habitats and threats to wildlife connectivity. “But we spend most of our time promoting public awareness so people can coexist with wildlife, and species like lynx and grizzlies can continue moving freely,” Buffler says.

That means, for example, partnering with citizens’ groups, municipalities and industry in order to manage the use of motorized vehicles in backcountry areas; to make dumpsters bear-proof so grizzlies don’t get into trouble and have to be killed; and to convince mining, logging and energy companies to fragment less habitat. “Our biggest challenge is to change public attitudes and behaviors,” Buffler says. One encouraging sign is a recent poll commissioned by his organization that shows 75 percent of residents in northwestern Montana’s Cabinet-Yaak Ecosystem believe grizzly bears belong there and should be preserved for future generations. “That’s a big increase from several years ago,” he says.

Protecting Linkages 

Another promising development: Governments are recognizing the economic logic in maintaining wildlife connectivity. “It’s a whole lot cheaper to protect wildlife corridors before doing things like energy development than to try to go in afterward and recreate them,” says Miller. In 2007, the Western Governor’s Association called for designing communities “in a manner that protects crucial habitats and maintains the ecological permeability of the intervening landscape so that wildlife can move between those areas.”

In 2008, the association created a wildlife council to advise them on where existing wildlife corridors would be damaged by proposed energy development. “The governors could see they were on a collision course, where their need to develop energy was conflicting with wildlife, which is hugely important out here,” Torbit says. “By mapping core areas and wildlife routes, development can still occur while keeping the landscape permeable to wildlife movement.”

For that to happen, however, government agencies must know which routes wildlife use and what landscape features inhibit movement. Jakes’s transboundary study on pronghorn will help. He overlays the pronghorn migration routes he has mapped on other maps that show gas wells, roads, farms, energy transmission lines and agricultural land in his study area. “I can see how pronghorn respond to these different developed areas as they travel,” Jakes says. For instance, one map shows a herd of pronghorn moving south until they hit U.S. Highway 2, after which they parallel the roadway for several miles before turning back north. “They don’t like to cross busy roads, so the highway is actually changing the trajectory of their movement,” Jakes says.

His observations underscore the need for protected corridors. Last February, for example, he tracked a herd of about 400 pronghorn that had suddenly headed south, fleeing brutally cold weather. One aerial photo shows the herd, which had been moving across the prairie in a single-file line stretching nearly two miles, stopped by a barbed-wire fence, one of several score they must negotiate on their biannual migration. “They are sitting down there, conserving energy, trying to figure out what to do,” Jakes explains. “It was almost 40 below, and they wanted to go south as fast as they could, but they were stuck.” He says eventually the pronghorn found a gap in the wire and continued their journey, then adds, “But that was just one fence.”

Tom Dickson is editor of Montana Outdoors magazine.

NWF at Work: Building a Wildlife Corridor in the Northeast

NWF’s Northeastern Regional Center in Montpelier, Vermont, is working with The Nature Conservancy and some 20 other private and public entities to create a vast habitat corridor that will connect six wildlife-rich landscapes (circles in map at left) in the Northern Appalachians and span a total of 80 million acres across New York, Vermont, New Hampshire, Maine and two Canadian provinces. Wildlife in the area includes such locally at-risk creatures as lynx, pine marten and fisher.

Funded by the U.S. Fish and Wildlife Service, the Staying Connected Initiative seeks to protect habitat from fragmentation and climate change and to restore landscape connections by assisting towns with protection of sensitive natural resources and by partnering with land trusts for permanent wildlife habitat protection.

“We want to empower local groups and citizens through education and outreach,’” says George Gay, senior manager of NWF’s Safeguards Program. “It works out really nicely from the National Wildlife Federation’s point of view, because it’s grassroots advocacy.”

Learn more about NWF efforts to safeguard wildlife corridors in other parts of the nation >>

The Long Haul

The 350-mile route used by pronghorns migrating between Grand Teton National Park and the upper Green River Basin in western Wyoming is the longest of any New World mammal south of central Canada.


"Perilous Journeys"—Just as science begins to solve the mysteries of their seasonal comings and goings, many of the world's migratory species are in sharp decline
NWF Launches Vermont Conservation Project
Conservation: Wildlife Corridors

Get Involved

Where We Work

More than one-third of U.S. fish and wildlife species are at risk of extinction in the coming decades. We're on the ground in seven regions across the country, collaborating with 52 state and territory affiliates to reverse the crisis and ensure wildlife thrive.

Learn More
Regional Centers and Affiliates