Global warming and development are driving certain animal species north in search of cooler temperatures and undisturbed land, but the Shiras' moose, native to the Rocky Mountains and parts of southern and western Canada, is taking an opposite path.
"They've been moving southward along the Rocky Mountains and presently are migrating farther and farther to the west," said Dale Toweill, trophy species coordinator for the Idaho Department of Fish and Game and the state's moose program supervisor.
"We know the first moose in eastern Washington appeared about 15 years ago, and they're now colonizing in eastern Oregon."
From Idaho and the Northwest to Colorado and Utah, moose populations are booming across the West, and not just in the deepest forests farthest removed from civilization.
In Idaho, alone, the moose population has doubled over the past 20 years and is currently estimated at 20,000.
"They're really doing well," Toweill said.
What's unique is that the surge can't be classified as a recovery, as current populations trump historic figures. "The moose population in the (Wood River Valley) has really established over the last 15 years...there were essentially none prior to that," said Randy Smith, wildlife manager for Fish and Game's Magic Valley Region, which includes Ketchum and the Wood River Valley. "Of course, you'd always get a wanderer or two moving through."
Now, moose sightings are no longer considered a rarity in the valley, especially along the Big Wood River corridor.
"We do know that throughout the 60s, 70s, and 80s, moose sightings in the area were pretty rare," Smith said. "Now we have a viable, established moose population that's breeding and sustaining and increasing in distribution every year."
Transplants are largely responsible for the population boom in Colorado and parts of the Northwest. But in Idaho, the surge is mostly due to a changing landscape.
The largest member of the deer family, moose were somewhat scarce in Idaho and much of the West prior to the 1940s, according to Smith. Since that time logging and grazing has decreased, farming practices have changed, and moose habitat has coincidentally improved.
In Idaho, the greatest landscape alterations have occurred across the state's vast agricultural area, where numerous farms have closed and once-tilled fields have given way to virtual forests thick with deciduous trees and shrubs—excellent moose habitat.
As a result, "Moose are moving into farm country—places that offer tree and shrub cover, and surface water," Toweill said. "And they're being attracted to housing (developments), since people like trees around their houses.
"They'll spend most of the day shaded up and are active primarily at night."
Riparian restoration projects, which have revived numerous Western streams damaged from over-grazing, irrigation and development, have also benefited moose across the West, Toweill said.
While most animal species generally suffer from human contact and development, Shiras' moose seem to use it to their advantage.
"What is not only possible, but likely, is that by making the landscape more favorable for ourselves, we have made it more favorable for moose," Toweill said.
The Shiras' moose—formally known as the Alces alces shirasi—is the smallest of four subspecies native to North America, weighing on average about 900 pounds. The largest moose, Alces alces gigas, found in Alaska and the Yukon, can weigh up to 1,800 pounds.
The Shiras' comparatively slender frame makes it more tolerant of heat, which is another reason it's able to survive and even thrive in former agricultural hubs, where summer temperatures can be balmy.
"They don't have a big, fat body, so they can get rid of heat more easily," Toweill said. In addition, the animal can co-exist with people "pretty well," as long as they're not directly disturbed.
Between enhanced habitat and protection—Idaho Fish and Game doled out just 864 hunting permits for bull moose, and 222 for cows last season—experts are not surprised that moose are thriving across the West.
But just what prompted the animal to migrate south and west isn't clear—moose and deer in the Yukon are migrating north.
"We still don't have any good reason," Toweill said. "No one knows exactly."
Eleven years ago, the U.S. Fish and Wildlife Service reintroduced 15 wolves in Idaho. A year later, another 20 were released. Wolves were also reintroduced in Yellowstone National Park and Montana, and today the population is believed to exceed 900 wolves between the three states, including over 500 in Idaho.
"Wolves are pretty effective predators on moose," Toweill said.
Effective enough to drive moose south in search of safer habitat?
"I'm not going to (say) that that is my speculation, but you do know how animals react to pressure," Toweill said. "If wolves are putting pressure on moose, they will go some place where there aren't wolves."