The researchers use animal tracking data to shed light on the fences that impede the movement of mule deer and thorn antelope
Berkeley – Every year, thousands of migratory deer and spiny-horned antelope travel northwest from their winter homes in the Green River Basin, a grassy valley in western Wyoming, to their summer homes in the mountainous landscape near Grand Teton National Park.
But to reach their destination, these ungulates must successfully sail the more than 6,000 kilometers (3,728 miles) of the fence that cuts across the area. That’s enough distance to stretch nearly twice the length of the US-Mexico border.
In a new study, wildlife biologists at the University of California, Berkeley, combined GPS location data of mule deer and cleft horn with satellite images of fences to see how often these animals encounter fences, and what happens when that happens. The results were published on January 7 in Journal of Applied EcologyHelp identify the fences that are the biggest barrier to ungulates trying to reach their ideal habitat.
Alongside the study, the team is also publishing a software package that helps wildlife managers around the world quickly analyze GPS tracking data to identify fences and other barriers that may hinder the animals’ vital movements.
“We need fences – they help keep livestock safe, can help separate livestock and wildlife, and mark property boundaries,” said Arthur Middleton, assistant professor of wildlife management and policy at the University of California, Berkeley and lead author of the research. “So, the question becomes, how do you identify which fences are really important, and which ones are a problem from a wildlife point of view, and then look for some way to mitigate the effects?”
Fences don’t always constitute an insurmountable barrier to wildlife, and different species find different ways to get around them. Mule deer are ready to jump over low enough fences. However, spiny-horned antelopes are reluctant to jump over fences and should instead look for areas where they can move underneath.
Wonging Shuo, PhD. A student at UC Berkeley and lead author of the paper, took these different behaviors into account when creating a software package that compares animal tracking data with fence maps. The program can categorize the different types of behaviors that animals may engage in when encountering a fence, such as crossing a fence quickly, moving back and forth along the fence, or turning and walking away from the fence.
To understand how fences affected mule deer and horn, Shaw began by comparing fence maps from the Federal Bureau of Land Administration and the U.S. Forest Service with satellite imagery, adding fences that were not included in government surveys. When all the fences were counted, Shaw was surprised at the sheer amount of fence in the area.
“The overall length of the fences is really amazing, especially with what we know about the different species of large-scale animals that live in that area,” said Shaw.
Shaw then compared these maps to Global Positioning System (GPS) tracking data that collected locations every two hours for 24 female mule deer and 24 fork antelope.
Shu found that every year, mule deer encountered fences 119 times. Horned antelopes encountered fences twice that rate, about 248 times per year. 40% of fence encounters resulted in a change in animal behavior.
“Anyone who’s spent time in the West knows you’ll find plenty of fences. But, seeing such frequent encounters, of which 40% lead to failures to cross, is kind of surprising – especially when you multiply these numbers across entire populations and landscapes.” Middleton said.
Some of these fences are currently used by farm owners to protect livestock or mark lines of ownership. Others, Middleton said, are relics of a bygone era when sheep farming was common in the state.
The best way to mitigate the impact of these fences on animal migration is to remove them, or replace them with “wildlife-friendly” fences over which the mule deer can jump or the cleft horn can bend underneath. However, both options require money and labor. According to Xu, a modern Wyoming fence modification project spent more than $ 10,000 per mile of fencing to make fences more porous for spiny antlers.
The software package developed by Xu is able to create maps that highlight which fences are the biggest barrier to animal movement, helping to prioritize fences to be modified or removed.
“There is an urgent need for this kind of data,” Shaw said. “Fences are really expensive to modify, and the amount of fences that would need repair is very large. [Wildlife managers] They really want to find ways to prioritize their resources. “
Brandon Scurlock, the Wildlife Department coordinator for the Pinedale District of the Wyoming Department of Fish and Games, is working to designate a sheltered migration “corridor” that connects the summer and winter ranges of rift antelope in western Wyoming. The country established similar migration corridors for mule deer earlier this year.
The Scurlock team is already using the study results to identify fences that may create barriers along these roads, and to prioritize modification.
“It was interesting to note the properties of some of these fences that this study indicated as highly impenetrable to Pronghorn,” said Scurlock, who was not on the study team. “We recommend that the bottom wire of the fence be at least 18 inches above the ground. When looking at some of the particularly nasty fences these approaches highlight, we always see that they have barbed wire very close to the ground.”
One option to offset the cost of easing the fence throughout this area, which is part of the greater Yellowstone ecosystem, would be to impose a small “protection fee” on visitors to the area’s parks, which include the hugely popular Yellowstone National Park and the Grand Teton National Park. Middleton and co-authors, including Berkeley law professor Holly Dormus, explored the feasibility of this approach in a study published last month in the journal. Conservation science and practice.
“The accurate movement data helped us see more in animal lives, including the challenges we posed,” Middleton said. Hope this work helps open people’s eyes to the range of fence effects. Our next steps are to understand the true biological cost that all of these fence-related behavioral changes have on wildlife populations, and to find ways to mitigate these impacts on a really large scale. ”
Other co-authors of the paper are Nandintsetseg Dejid of the Senckenberg Center for Biodiversity and Climate Research (SBiK-F) in Frankfurt, Germany; Valentin Hermann of the Smithsonian Institution of Conversational Biology; Hall Sawyer of the Western Ecosystems Technology Inc.
This research was supported by the National Geographic Society (Grant / award number WW-100C-1), the Buffalo Bill Center for the West, the William and Flora Hewlett Foundation, the Greater Yellowstone Alliance, the Knobloch Family Foundation, the Smithsonian Conservation Biology Institute and the German Federal Ministry of Education and Research (Grant number / award BMBF01LC1820A)