The secret lives of fences
Written by Emily Reed
Most all of Wyoming’s ungulates (hooved-animals) are migratory. For migrating wildlife in the West, it’s all about having access to seasonal habitats. In order to find the routes that provide access to high-quality forage, ungulates like mule deer, elk and bighorn sheep have to learn them by following in the hoof-prints of their mothers or other animals in the herd. Most calves and fawns are only four to five months old when they learn their migration route for the first time. In the first autumn of their life, they scamper up and over mountain passes and ford rivers and creeks to get to their winter range, a journey that can stretch for up to 150 miles or longer for certain individuals.
A doe and her yearling fawn munch on spring vegetation emerging along the foothills of the Wind River Range near Pinedale, Wyoming. Credit: Gregory Nickerson
However, many animals are struggling to migrate in the face of increasing challenges. Our ever-expanding human population and footprint alter their habitats, hindering their ability to find the best forage. The steady increase of subdivisions, roads, fences, energy production, and mineral development have big implications for the future health of these big game herds. And, researchers have found that climate changes has increased the frequency of drought, which reduces the duration of springtime foraging that animals rely on to get them through the long winters.
A mule deer buck searches for a way around an elk fence. Credit: Joe Riis
Fences are often an overlooked challenge to animal movement, they are a dynamic barrier to wildlife because they can be built quickly compared to other infrastructure, and they can also deteriorate rapidly. Fences crisscross the western landscape marking property boundaries, lining the right of ways on highways, keeping livestock corralled, and more. Biologists are responding by conducting detailed assessments of fences and the impacts they have on wildlife at large scales.
Destin Harrel looks at mapped fences while out in the field. Credit: Emily Reed
Just this year (2020), a team of researchers lead by UC Berkley PhD Student Wenjing Xu from the Middleton Lab produced one of the first large-scale estimates of fence density in the western United States. Their model estimated that there are more than 1 million kilometers (km) of fences, without including urban and suburban property fences. They also found that nowhere in the western U.S. are you more than 48 km away from a fence, with the average distance being 3 km.The model further shows high densities of fencing around urban areas, and lower densities around rural and remote parts of the western United States. However, several areas in north-eastern Wyoming and Idaho as well as western Colorado stood out as having high densities of fencing despite their remoteness from human urban areas.
This underscores the idea that vast areas of land that seem untouched by the human footprint can be secretly covered in dense networks of fences. Animals like moose and elk are able to easily step over and hop over standard fences with their long legs, but other species like mule deer often die by getting their legs caught in the wires while jumping over them. Pronghorn especially struggle with fences because they don’t like to jump over them, they prefer to duck underneath the bottom wire. Pronghorn will often be delayed or even get stuck between fences on their migration routes. Sometimes they can get stuck in small, fenced areas for a year or more. When these species start their fall migration, they often have their fawns or calves in tow, who are not fully grown yet and struggle to leap over the fence or find gaps in woven wire fences to squeeze through.
Moose caught in fence wires. Credit: Jackson Hole Wildlife Foundation
Other wildlife like Sage grouse also are impacted by fences,. The birds can’t see when flying and each spring across the West they collide with fences when flying from their traditional leks (breeding grounds). Fences can also provide hunting raptors a place to perch.
A sage grouse hen in the YU bench area outside of Cody, Wyoming. Credit: Emily Reed
All of this is an easily fixable problem, by identifying where fences impede big-game wildlife movement from detailed maps. This allows citizen efforts and private-public partnerships like the Absaroka Fence Initiative to implement wildlife-friendly fence designs to ensure that we will have robust big-game populations and other wildlife like the sage-grouse to enjoy for future generations.
AFI participants work on a fence. Credit: Kathy Lichtendahl
