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For a species so historically associated with free-range migrations, bison today are among the nation's most constrained wildlife species.

Within the continental U.S., only Utah allows its wild bison to roam where they will.

Yellowstone's herd spills over from Wyoming to Montana but is tightly controlled once outside the park. Badlands and Theodore Roosevelt national parks in the Dakotas fence their herds. Wind Cave National Park conducts roundups. Steep mountains contain Grand Teton's small herd. Commercial bison ranches abound in the West, but most state wildlife agencies don't truly treat any of the animals as free wildlife the way they would elk or deer.

"Utah is it," Yellowstone National Park bison biologist Rick Wallen said. "It's a really unique scenario."

Starting with 18 Yellowstone transplants, Utah re-established its wild herd in the 1940s, starting where Garfield County's remote Henry Mountains rise from the dry Colorado Plateau to snowy peaks above 11,000 feet. That herd has grown to about 300 adults, and, in recent years, biologists have transplanted 70 to eastern Utah's Book Cliffs, where the state's objective also is 300.

"They are wild animals, and we manage wildlife," state big-game project leader Kent Hersey said of Utah's approach. "When you start putting in fences, it's more like livestock."

Both areas are remote and relatively conflict-free, though ranchers or game wardens sometimes must chase bison away from cattle-grazing allotments in the Henry Mountains. These wild herds are not to be confused with the bison on Antelope Island State Park, where annual roundups control the population.

Utah allows hunting on the Henry Mountains herd, but it's by once-in-a-lifetime lottery drawing and only 34 permits were awarded last season. The state intends to allow hunts in the Book Cliffs once that herd is fully established.

Like its source herd in Yellowstone, Utah's bison population developed the calf-aborting disease brucellosis decades ago. In 1962, Hersey said, the state managed to round up 69 of the 70 animals then in the Henrys and eliminate those that tested positive. The disease has not been known in Utah bison since.

If Utah's bison contracted brucellosis again, he said, biologists would manage the disease — not fence the herd.

Wallen said it isn't so easy everywhere bison live, partly because of cattle conflicts, but also because bison can be ornery and gore people who don't give them wide berth.

Migration map

In severe winters like this one, hundreds of bison seek relief from the deep snow. To see a map, visit