Fence removal, modification aiding Yellowstone wildlife

Fences are meant to keep animals in or out, not to let them through.

But a unique partnership has been forged specifically to help pronghorns crawl under fences outside Yellowstone National Park’s North Entrance along their migration route to the Paradise Valley, a historic winter range.

Since 2010, the National Parks Conservation Association has received funding from Nature Valley to remove or alter about 18 miles of fence. The group has partnered with students, the Bureau of Land Management, Yellowstone Park, the Forest Service and the Fish, Wildlife and Parks’ area biologist to complete the work.

“We try to be strategic with the fences we remove or modify,” said Stephanie Adams, program coordinator in the NPCA’s Bozeman office.

The NPCA is doing similar work in Grand Teton National Park in Wyoming to help pronghorns that migrate from the park up to 170 miles south to the Upper Green River Basin — one of the longest animal migrations in North America.

Remove or modify

Early on, NPCA and its volunteers removed old fencing no longer needed on Gallatin National Forest lands, Adams said. Last Friday, the workers finished rebuilding a fence around the BLM’s 130-acre Carbella fishing access site along the Yellowstone River.

After taking out the old fence, a new enclosure around the site was built with smooth wire 18 inches above the ground on the bottom. That’s important since pronghorns typically won’t jump a fence, preferring to crawl under. The top wire of the fence was also set lower than usual to allow other wildlife such as elk and deer to more easily jump over.

Moving on

Pronghorns summer in Yellowstone’s Northern Range, along the Yellowstone and Lamar river valleys. In winter, they migrate out of the park to avoid deep snow that covers forage. To trek out of the park, they follow the Rescue Creek Trail from Blacktail Deer Plateau, behind Mount Everts and down to the Gardiner Basin — a 15-mile mountain trek that’s unusual for the prairie dweller. From Gardiner Basin, they walk along an old railroad bed through narrow Yankee Jim Canyon to reach the Paradise Valley, an 18-mile trip.

Although called antelope, the animals are not true antelope such as those found in southeast Asia and Africa. Instead, they are a species that evolved over the past 20 million years in North America to outrun cheetahs and lions that once inhabited the continent. Their main defenses to avoid predators are sharp eyesight and the ability to run up to 45 mph. That’s key because they aren’t very big, standing about 3-feet tall at the shoulder with large males tipping the scales at 125 pounds.

Unfortunately, young pronghorn fawns take a few weeks to learn how to run, so they are the most susceptible to predators, which may be one reason their population plummeted in Yellowstone.

Studies of the animals’ decline in Yellowstone found high fawn mortality blamed on predators — mainly coyotes. As wolf numbers climbed after they were reintroduced to the park in the mid-1990s, coyote numbers fell since wolves see them as competitors and will kill them. This canine rivalry may now be benefiting pronghorns.

Comeback

Yellowstone’s and Paradise Valley’s pronghorn population has rebounded in the past few years after hitting historic lows.

About 1,000 pronghorns were removed by the Park Service between 1947 and 1966 out of concern that there was too little sagebrush to feed the animals. In those decades, pronghorn numbers fell from 700 to 150, according to a study published by P.J. White, chief of wildlife and aquatic resources at Yellowstone National Park.

After staying low for a couple of decades, the pronghorn population jumped to about 600 between 1982 and 1991 and then crashed in the early 1990s to about 235 animals and stayed at that level through 2006.

It was in the late 1990s that some of the pronghorns began staying in the Paradise Valley rather than migrating back into the park in spring, said Karen Loveless, FWP wildlife biologist in Livingston, Montana. From about 26 animals counted in 2002, the nonmigratory herd grew to 105 last year. The herd mainly lives on private agricultural lands between Rock and Big creeks on the west side of the Yellowstone River.

“In the Paradise Valley there’s just some really good habitat for them in there,” Loveless said. “And they’re having good reproduction.”

Spreading out

Since this group has established a new range, Loveless said she’s seeing more antelope in the Paradise Valley farther north. Yet she’s unsure if they are coming from the southern herd or have migrated south from around Livingston, where the pronghorn population has remained strong.

There’s no hunting season for pronghorns in the Paradise Valley, partly because the animals are always on private land, where landowners aren’t interested in providing public hunting access.

This year, Loveless counted almost 500 antelope from Yellowstone and Paradise Valley combined.

With passage to their traditional wintering grounds less obstructed and herd populations growing, pronghorn in Yellowstone’s northern range look poised to rebound. That’s good news since Yellowstone classifies its pronghorn population as a species of special concern out of fear that disease or a hard winter could wipe out the small herd. However, one study found that Yellowstone’s herd may not support more than 500 pronghorns for long periods because of winter range habitat deficiencies in the Gardiner Basin. But if a migration corridor to the Paradise Valley is easier for pronghorns to negotiate, perhaps the use of the Gardiner Basin will diminish even as the herd grows.

The NPCA’s Adams said she hopes to continue the fence modification project another 15 miles north to the small town of Emigrant, close to the middle of Paradise Valley, to give pronghorns more room to safely spread out.

“I hope that Nature Valley will continue to support the project because we’re seeing such great results on the ground,” she said. “And we’re engaging the public and school groups on land issues.”