Deer Migration Map

The University of Wyoming has detected a new mule deer migration that runs all the way from the Red Desert to the Island Park, Idaho, area. That’s a record-setting 242-mile journey.

One of the longest-recorded mammalian migrations on Earth has been discovered passing through Jackson Hole, northwest Wyoming and well beyond.

A University of Wyoming-tracked research mule deer that winters in the Red Desert not far from I-80 hoofs it all the way to summering grounds near Island Park, Idaho, making a 242-mile trip.

It’s a migration route that Matt Kauffman and his Wyoming Migration Initiative colleagues first suspected in 2016, but couldn’t prove because the tracking collar on the doe called deer No. 255 failed shortly after she landed in eastern Idaho. Then she resurfaced.

“For almost two years she was just gone,” Kauffman said. “When we captured her, it was completely random.”

The doe reappeared on researchers’ radar in March when contracted helicopter pilot David Rivers spotted her brown, off-the-air tracking collar while flying the Red Desert. She was captured and, voila, same deer.

Deer No. 255’s presence back on the winter range south of the Wind River Range put to rest suspicions that she was a “disperser” who had abandoned her Sublette Herd counterparts to live out her days with another herd.

A segment of the Sublette Herd of mule deer already claimed the longest known deer migration in the United States, an approximately 150-mile path that skirts the Winds’ east slope between the Hoback River basin and the Red Desert. Deer No. 255 deviated from that route, which wasn’t uncovered until 2013, when she kept pressing north.

She continued along the southwest flank of the Gros Ventre Range, using a path paralleling the Granite Highline Trail before she crested the eastern part of the range between Nowlin and Jackson peaks. From there, the doe skirted Slide Lake, shot north through the Leidy Highlands and entered Grand Teton National Park near Spread Creek. She passed by Moran and followed the east shore of Jackson Lake before crossing through John D. Rockefeller Jr. Memorial Parkway and the Jedediah Smith Wilderness on the way to cutting the corner of Yellowstone National Park. Home for the summer took nearly three months to reach, and was a 2-square-mile patch of meadows, wetlands and lodgepole pine outside Island Park.

It’s likely that relatively few deer make the lengthy biannual journey, Kauffman said.

“We’ve collared over 100 animals in the Red Desert,” he said, “and this is the first one to do that. She’s probably not alone, but probably not one of thousands of animals to do this. Maybe not one of hundreds.”

Why the doe goes 200-plus miles to Island Park is “kind of unknowable,” Kauffman said, but he had a theory that might explain that behavior.

“She could have had an Island Park summer range,” he said, “and maybe she just wintered around Jackson until a big winter came and then she headed down to the Upper Green or Pinedale.”

Another big winter could have nudged the doe’s ancestors even farther south, until they learned to access the inviting low-snow winter range of the Red Desert. Or the script could be reversed: Deer No. 255’s migration could have started with a group of animals that wintered near the interstate and summered in the Hoback, until there was a dry summer with poor forage that sent them searching for more productive surroundings.

The confirmation of the record migration has wowed biologists, who continue to make discoveries about mule deer movements in the Yellowstone region.

Grand Teton National Park biologist Sarah Dewey has tracked newfound deer migrations connecting Jackson Hole to winter ranges near Rexburg, Idaho, the Bighorn Basin, and Green and Wind river drainages.

She told the University of Wyoming, “Mule deer continue to amaze me.”

“We’re learning that Grand Teton National Park sits at the center of a complex network of migration routes radiating out from the park in all directions,” Dewey said in a press release.

Researchers are following Deer No. 255’s spring migration, which is already underway. She was last marked at Steamboat Mountain, about halfway between Highway 28 and I-80, and is likely reach Hoback in a month to six weeks, Kauffman said.

Time will tell if she’ll stay put or keep going, tracing her 2016 route all the way to Island Park.

Kauffman pointed out that it’s the Greater Yellowstone Ecosystem’s protected lands, big open country and dearth of people that make such a journey possible.

“It’s not a mistake that we’re discovering this type of thing in northwest Wyoming, because it’s one of the wildest places in North America,” he said. “Those are the types of landscapes where migrations persist.”

Contact Mike Koshmrl at 732-7067, env@jhnewsandguide.com or @JHNGenviro.

Mike has reported on the Greater Yellowstone Ecosystem's wildlife, wildlands and the agencies that manage them for 7 years. A native Minnesotan, he arrived in the West to study environmental journalism at the University of Colorado.

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