Each spring, a herd of mule deer leaves the Red Desert and follows a trail of greening grass and retreating snow along the western slope of the Wind River Range. Months later, the animals arrive in the Hoback Basin south of Jackson, more than 150 miles away.
It is the longest recorded mule deer migration in the world, and an ancient rite vital to the long-term survival of Wyoming’s iconic mule deer populations.
And its future is uncertain.
The journey from desert to mountains takes the herd over fences and across roads, near subdivisions and through narrow passageways flanked by towns and lakes. There are no National Parks or wilderness areas to offer refuge. The deer contend with the elements and whatever obstacles people put in their way.
Scientist believe the migration has lasted this long because large swaths of land between the deer’s summer and winter ranges have remained undeveloped.
In many ways the migration, like bison roaming the plains, is a symbol of the old West. It is a possibility only states like Wyoming can still offer, and one that may not always remain.
“We’ve been blind to a large chunk of this migration to date, and been fortunate that that landscape has remained intact,” said Hall Sawyer, a researcher at Western Ecosystems Technology Inc. who discovered the migration. “But it’s important for us to understand where this route is so we can take a proactive approach in helping shape future land use practices.”
Researchers didn’t even know the migration existed until two years ago.
The Bureau of Land Management had contacted Sawyer to find out where a group of deer living in the Red Desert call their winter and summer ranges.
Sawyer, 43, has studied elk, pronghorn and deer migrations for two decades. He also uncovered the famous pronghorn herd that travels more than 100 miles from the Upper Green River Basin near Pinedale to Grand Teton National Park, which, until now, held the title of longest migrating mammal in the Lower 48.
In 2011, Sawyer caught and collared 40 deer east of Rock Springs for the BLM study and commissioned a pilot to track the herd. Yet following the deer proved more difficult than expected. On the first flight, the pilot found only a few.
Sawyer asked him to fly even farther north, near Pinedale, to see if they’d joined deer on the south end of the Wind Rivers. The pilot called an hour later and said he picked them up, 100 miles away from where they’d started.
“That was the beginning of it,” Sawyer said. “It took us a couple of flights to make sure this was really happening. Then I thought, ‘How will we have the flight budget to fly half of the state of Wyoming looking for deer?’”
He discovered that a group of about 500 mule deer starts north of Rock Springs, winding 50 miles through canyons and past sand dunes to join almost 5,000 more. The mass then snakes like a living train for another 100 miles. The original group ultimately climbs 3,000 to 4,000 feet in elevation.
Sawyer finished his project for BLM, at the same time working with Matt Kauffman, leader of the Wyoming Cooperative Fish and Wildlife Unit at University of Wyoming and director of a new effort called the Wyoming Migration Initiative.
The scientists believed the mule deer migration fit perfectly with the initiative, which was created to connect migration research with groups working on wildlife issues.
“We recognized that although there was an incredible amount of interest and people wanted to wrap their heads around migration, the science wasn’t getting applied to the effort,” Kauffman said. "I remember that meeting ... at one point Hall simply said, 'This (Red Desert to Hoback) migration is the story the WMI should tell.'"
The pair decided to document the migration in video and photographs and contacted Joe Riis, a National Geographic photographer based in Wyoming who tracked the pronghorn migration. They wanted to combine the intrigue of deer wading through rivers, crossing roads and calling out to each other with the practical science of conservation and mapping.
About 90 percent of Wyoming’s big game migrates from one area in the winter to another in the summer, Kauffman said. It might be from the foothills of Casper Mountain to its summit, from the Red Desert to the Hoback, or some distance in between.
Migration, he said, is what sustains many of Wyoming’s herds. It is how big game has evolved and learned to live in the harsh, high plains known for long, bitter winters and dry, windy summers.
Deer often stay in the mountains in the summer, gorging themselves on luscious, green plants and shrubs while building a critical layer of fat meant to carry them through most of the winter.
The herds move down to the plains when the snow begins to fall. There is less food, but they do not have to contend with the potentially deadly combination of deep snow and subzero temperatures.
Come spring, they move back toward greener pasture.
Some deer remain on their winter ranges all year, eking out a living on what little remains. Most of them move on.
“It’s a trade-off between making the long, dangerous migration and getting some good groceries, or staying in the desert where you don’t have to migrate but have slim pickings,” Sawyer said. “It’s nice to see that the population didn’t put all their eggs in one basket. Some go all the way, some pop up a little ways, and other stay put.”
Wyoming would still have deer even without migrations. Does would munch on tulips in backyards and fawns would be raised on golf courses, Sawyer said.
But backyard deer are a drop in the bucket of Wyoming’s overall population. They number in the hundreds when migratory herds number in the tens of thousands.
“These migratory herds are our bread and butter,” Sawyer said.
To anyone who has seen a mule deer clear a fence, such a barrier may not appear to be an obstacle.
But 100 fences, combined with rural subdivisions, highway crossings and bottlenecks, are more problematic, Sawyer said.
Sawyer and Kauffman highlighted 10 potential problem areas for deer and their passage between the desert and the Hoback. They range from 8-foot-tall fencing on feedgrounds to Bureau of Land Management lands available for oil and gas leasing.
What makes the herd so remarkable – that they travel through unprotected land – is also what makes their seasonal journey so perilous, Sawyer said.
Instead of traveling through a wildlife refuge or National Park, they move over a mix of BLM, state and private land.
Sawyer not only detailed where the deer go, but also where they stop for nourishment. Deer travel in some ways like people, moving long distances and stopping in key areas for food and rest. Developing in those resting areas would be like removing hotels and restaurants from towns along interstates, Sawyer said. Without a stopover, deer could miss important groceries along the way.
But now that researchers know where the deer travel and where and when they stop, land management agencies, conservation groups and landowners can focus their efforts on the critical areas, he said.
The Wyoming Department of Transportation, for example, has agreed to lower the top wire on fencing surrounding one of the key highway crossings, Sawyer said.
Nonprofits now know what areas could be important for habitat projects or fence changes.
The research and outreach effort connects science to boots on the ground, said Steve Kilpatrick, executive director of the Wyoming Wildlife Federation.
“If we don’t have science, we use our opinion to paint a broad landscape. With science, we know we have a narrow band and what can we do to help the band,” Kilpatrick said. “The important parts of those migration routes are absolutely essential to the long term well-being of our big game herds in Wyoming.”
Kauffmann and Sawyer believe the migration rivals the wildebeests’ trek across the Serengeti or the caribou’s journey over the Canadian tundra. They compiled a report aimed at raising awareness of the journey, aided by photos and video from Riis, the National Geographic photographer.
Today, many states have had their wild places filled in with subdivisions, shopping centers, industrial development and crop lands. The days of the great bison herds moving across the plains have long since ended. Most big horn sheep no longer cross from one mountain range to another.
But Kauffman and Sawyer say there's hope. With a little planning, Wyoming’s mule deer migrations and others like it will endure in one of the last truly wild places.