Bits of hide flutter in the wind as they dangle from a cloven-hoofed foreleg entangled in fence wires. The rest of the carcass lies scattered by scavengers at the base of the fence. If you’ve spent time in the rangelands of the United States or Canada, you’ve likely seen this grim pennant. It marks the spot where a wild animal attempted to cross a fence and failed. It’s a heartbreaking scene. For Paul Jones, senior wildlife biologist with the Alberta Conservation Association, it’s also a call to action.  

Today Jones studies how to make fences safer for wildlife. But Jones and fences have a long history. An early summer job with Alberta’s Department of Fish and Wildlife required supplying farmers with fencing that kept deer and elk from raiding their stacks of hay.

Those fences made it easier for farmers and ranchers to share rangeland with wildlife, but it comes at a cost. A 2005 study of fences along roadways in Colorado and Utah estimated that for every two and a half miles of fence, one antelope, deer, or elk is killed annually. The study found that most of the animals killed had caught a leg in the fence as they tried to jump over, couldn’t pull free, and ultimately died from exposure. Unfortunately, we lack much of the basic information necessary to assess how big a problem fences pose for wildlife. For instance, how many miles of fence are there on North America’s rangeland? “That,” Jones says, “is the million-dollar question.”

Many different individuals and agencies put up fences: private landowners, federal, state and provincial land management agencies, transportation departments, and railroads are just a few of them. These groups and individuals may have different record-keeping systems, if they record fence locations at all. Jones thinks the lack of records could just be the result of a lack of awareness. “People don’t really realize the potential impact that fences have on wildlife,” he says. “They’re an invisible barrier.”

Jones has spent the last 15 years studying pronghorn, which migrate hundreds of miles from as far north as southern Alberta and Saskatchewan to as far south as New Mexico. These exotic-looking speedsters are commonly referred to as pronghorn “antelope,” but they are technically not antelope at all—they are actually more closely related to giraffes than they are to true antelope or deer. Fences are especially problematic for pronghorn because, even though they are the fastest land animal in North America, they are lousy jumpers.

Prior to the introduction of fences beginning in the 1870s, there were few vertical obstacles on the grasslands and shrub steppes where pronghorn live. When confronted with a fence, they often try to crawl under it. If the bottom wire of the fence is barbed or too low, it will scrape the fur off their back. This may seem like a minor injury, but losing valuable insulation during a blustery Wyoming winter can have fatal consequences.

Many wildlife agencies and nonprofit groups including the Arizona Antelope Foundation and the American Prairie Reserve, are working to remove or modify the fences that impede pronghorn migration. But to understand, and hopefully mitigate, the impact of fences on species like pronghorn, researchers need to know where the fences are.

Record keeping is improving in some areas. In Colorado, the Bureau of Land Management uses National Environmental Policy Act (NEPA) standards to assess the impact of proposed fences on the lands it manages. The agency also records GIS data on fence locations. But some fences on the landscape today were first erected before NEPA went into effect in the 1970s. Many more predate the inexpensive GPS devices that now make it relatively easy to record locations and make maps.

Many fence lines are not visible from roads, so Jones has, at times, tried to map them using aerial photographs. This has its own challenges, since fences can be virtually invisible viewed from above. What are visible are the paths that cows sometimes leave walking alongside them, but a cow trail does not indicate what type of fence is next to it.

Concern for privacy is also an issue when it comes to mapping. Many landowners don’t want the location of their fences to become widely available. Jones is sympathetic. “I wouldn’t open my home’s door to a complete stranger to see how I decorated,” he says, “Their ranches are their home.”

Despite their hazards, fences can benefit wildlife in some situations. Keeping large mammals off highways saves the lives of motorists and the animals themselves, especially when fences are used to direct them to specially constructed wildlife crossings. Keeping wild herbivores separate from livestock can prevent the spread of disease. Fences can even be useful for managing the grazing of wild animals.

One example is the 113,613-acre Flying D Ranch near Gallatin, Montana, owned by billionaire Ted Turner. An avid conservationist, Turner wanted to turn back the clock on the ranch to resemble the state it was in before European settlers arrived. Most of the fencing was removed from the interior of the property, and the resident bison herd was allowed to graze freely. “The elk and bison keyed in on specific areas of good habitat, overgrazing them extensively,” says Mark Kossler, vice president of ranch operations. The preferred grazing areas began a downward spiral of habitat degradation, erosion, and loss of plant species.

Eventually the ranch installed a small amount of fencing (approximately 20 percent of what had originally been on the property) to divide the ranch into large pastures. This allowed managers to give pastures a period of rest from grazing, which allowed range health to recover. In the case of the Flying D Ranch, fences benefitted wildlife.

Many state wildlife agencies publish guides for land managers who want to make their fences safer for local wildlife. For instance, if the bottom wire on the typical four-wire cattle fence is replaced with a smooth, unbarbed wire that is at least 18 inches off the ground, pronghorn can pass under it unharmed. Spacing the top two wires of a fence 12 inches apart makes it easier for a mule deer to free itself if it becomes entangled. Flying sage-grouse sometimes hit fences and injure themselves, but attaching inexpensive strips of reflective material to the top wire of fences can prevent these collisions.

As wildlife face pressures from expanding human development and climate change, it is important to understand how our fences affect animals' ability to use their remaining habitat and relocate to new areas. Even if we knew where all the fences were, counting the numbers of animals caught in them would not give a complete picture of their impact, because they can also harm wildlife by blocking migratory routes and access to resources like water.

A significant amount of fencing on the landscape is not even needed anymore. Old fences are often left on the land because removing them is labor intensive. Even when no longer standing, these fences can still snag wildlife—or even wildlife biologists. “The first fence I ever took out was a bunch of downed wire that I got caught up in myself," says Brian Holmes, a biologist with Colorado Parks and Wildlife. “I thought, ‘Someone should take this out.’”

Since then, Holmes, with the assistance of grants from the Rocky Mountain Elk Foundation, the youth conservation corps, and a crew of volunteers, has now removed about 45 miles of obsolete fencing on state, private, and federal land over the last three years. Many conservation and hunting organizations—including the American Prairie Reserve, Wyoming Wildlife Federation, and Oregon Natural Desert Association—organize similar efforts.

The more people are aware of the problems that fences pose for wildlife, the more visible these “invisible barriers” will be. Many volunteers are happy to do the manual work of fence removal because they care about wildlife. Advancing  technology is making it easier to map fence locations and better understand their impact.

Our fences often harm wildlife, and a fence-free “open range” across western North America is not a realistic goal. But if we can remove unnecessary fencing, while making existing and future fencing safer for animals, we can go a long way toward being better neighbors to wildlife.