MISSOULA, Mont. — Wildlife must move to find resources and landscape connectivity is critical for their survival but fences and other linear features such as roads and railways can create obstacles to movement and contribute to population declines. Despite the extensive use of fencing globally, its impacts on wildlife are difficult to quantify due to a widespread lack of data.

A new study offers tools to evaluate the effects of fences on wildlife migrations in southwest Montana, using both modeling techniques and high-quality satellite imagery. When paired with wildlife location data, these maps can elucidate a far more accurate picture of how fence density and fence type impact daily and seasonal movements. The results of this study were highlighted in Advancing fence datasets: Comparing approaches to map fence locations and specifications in southwest Montana published in Frontiers in Conservation Science as a part of a collection of scientific papers focused on fence ecology.

“We simply don’t have maps for fences in the way we do for roads or buildings. And this is a huge limitation for wildlife ecology given the extent of fencing on the landscape and the rapid pace of habitat change occurring across the globe,” said Simon Buzzard, senior coordinator for Wildlife Connectivity at the National Wildlife Federation and lead author of the study. According to Buzzard, southwest Montana is home to a diversity of wildlife species that must migrate to find food, shelter and suitable breeding habitat but fences can get in the way. “High-quality data can help landowners and resource managers prioritize conversions to wildlife-friendlier fence designs to ensure wildlife can continue their migrations into the future,” Buzzard said. 

Fencing is a fixture of working lands in the West and proven strategies exist to build fences that are less of a hindrance to migrating wildlife while keeping livestock contained. In addition, conservation partnerships can provide the necessary resources to modify fences to wildlife-friendlier designs in priority areas. Increasing the bottom-wire height to 18 inches allows for pronghorn and juvenile elk, moose and deer to cross under a fence while lowering the top wire to 40 inches helps jumping animals avoid entanglement. 

However, the study found only 3% of sampled fences in Beaverhead and Madison Counties had wildlife-friendlier bottom wire heights of 18 inches or higher, and only 6% had top-wire heights measuring 40 inches or less.

“This is what you might expect, given that historically, fences were likely not built with wildlife in mind. But now we have the science, the capacity and the relationships we need to revisit this and create something that works for both wildlife and people,” said Jim Berkey, director of the High Divide Headwaters program in southwest Montana for The Nature Conservancy, an organization that assisted with the study.

The study also found that fences on public lands were not, on average, more wildlife-friendly than fences on private lands in this region of southwest Montana. This area is a patchwork of private and public lands, and recent movement data shows extensive pronghorn migrations (some reaching 200 miles roundtrip) across land boundaries and the state border into Idaho.

“Identifying fences on a map gives a basis for partnerships to rally around and target conservation efforts, leading to more available habitat for wildlife on the move," said Andrew Jakes, Great Plains Science program manager for Smithsonian's National Zoo and Conservation Biology Institute and co-author of the study.

There is greater attention at the federal level to provide funding and policy directives for federal agencies to work with states to conserve migration routes, such as the Bureau of Land Management’s Habitat Connectivity on Public Lands Instruction Memorandum. In addition, several western states such as Colorado, Nevada, Wyoming and New Mexico have executive orders or state laws in place protecting migration corridors. These, and other policies, can help provide funds and data analysis to prioritize fence modifications to wildlife-friendlier standards where it’s needed most.