Mulies on the move

Scientists discover a surprising migration in western Wyoming.

  • Mule deer are one of the West's most common species, but only recently has modern technology allowed humans to piece together their movements across the landscape, including a 300-mile round-trip migration route in western Wyoming. All summer these deer gorge on forbs and grasses in the Gros Ventre Mountains. Come fall, they must leave or risk getting trapped in building snowpack.

    Joe Riis
  • A map shows the mule deer migration path, covering a 300 mile round-trip through western Wyoming

    © 2014 Atlas of Wildlife Migration: Wyoming's Ungulates
  • Along their journey, they splash through Pine Creek in a narrow spot between Pinedale, Wyoming, and Fremont Lake.

    Joe Riis
  • A doe glances at a camera trap at one of many creek and lake crossings along the migration path.

    Joe Riis
  • A young buck mule deer navigating an elk fence. Deer can't clear the high elk fences, which are designed to keep elk off private land.

    Joe Riis
  • A herd of migrating mule deer skirts along a residential area in the Upper Green River basin.

    Joe Riis
  • By winter's end, the deer have been losing weight for months and are nearly starved. Their journey back to the mountains helps them make the most of Wyoming's short growing season and put on fat to survive the next winter.

    Joe Riis
  • A herd of mule deer shakes off after crossing the Fremont Lake outlet just north of the town of Pinedale.

    Joe Riis
  • A doe mule deer crosses a road at the southern end of Fremont Lake near Pinedale. This area is a pinch point for many deer.

    Joe Riis
  • Three buck mule deer in their summer range, above 10,000 feet in the Hoback Mountains.

    Joe Riis
  • A mule deer buck migrating south through boulder fields in the foothills of the Wind River Mountains, just east of the town of Farson, Wyoming.

    Joe Riis
  • A large buck picks his way along an elk fence looking for a way through. Eventually, the deer get into rolling sagebrush along the Wind River foothills and head south toward their Red Desert winter range.

    Joe Riis
  • A herd of mule deer on the move. They often travel in early morning and evening, and sometimes at night.

    Joe Riis
 

Hall Sawyer, a biologist for an environmental consulting group, was sitting in his office in Laramie, Wyo., in May 2011, when his phone beeped. It was a text message from the pilot he'd hired to fly over the Red Desert northeast of Rock Springs to locate 40 mule deer. Sawyer had radio-collared them to track their movements for the Bureau of Land Management. The pilot was searching for signals across a 40-mile area, but coming up short.

Sawyer told him to keep looking. As the plane skimmed north along the Wind River Mountains toward Pinedale, his receiver began to blip: The missing deer were scattered along the foothills – a whopping 100 miles north of where Sawyer expected them.

Sawyer, who has studied western Wyoming's deer and antelope migrations more thoroughly than anyone else, had expected this herd to roam year-round in the Red Desert near Rock Springs. So he was floored when, two years after that flight, radio-collar data revealed that the deer travel the same 150-mile-long corridor every year – the longest known mule deer migration. It's a carefully honed survival strategy: Their winter range is in the bony, dry desert with towering dunes and scrubby sagebrush, where little snow falls, leaving shrubs and spindly grasses exposed for them to graze. In spring, they follow the green-up, migrating up in elevation and north along the Wind River foothills, past farm fields, around glacial lakes and subdivisions, across the Green River and into the Gros Ventre Mountains, where remnants of huge snowdrifts hunker on the leeward ridges. And, where drifts have retreated, there are sprigs of new grass, nutritious wildflowers and trickling streams.

Surprisingly, this epic trek spans an unprotected landscape, far from the national parks, designated wilderness areas or other protected areas that often help support long-distance migrations.

Sawyer and others recently launched the Wyoming Migration Initiative to share the stories revealed by this and other studies. As energy development, housing, fences and roads squeeze – and sometimes sever – migration corridors, they want to ensure that conservationists and land managers have access to the best data showing how ungulates move over the landscape.

The seasonal paths wildlife travel are more likely to be blocked or bisected than ever before, and scientists fear that many large mammalian migrations around the world have blinked out altogether. But in sparsely inhabited western Wyoming, where vast open spaces support some of North America's largest and most diverse ungulate populations, hoofed creatures still undertake dramatic journeys. Without this migration, fewer deer would call the Red Desert home and none would survive in the mountains. "If we want to sustain the numbers of ungulates we have today," Sawyer says, "we need to take care of those migration routes."

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