Watch a mule deer punching through a deep, sharp-crusted snowpack, or gnawing a barren shrub in a whiteout, and it's hard not to think: well, she looks miserable.
Now take a gander (not that many people are lucky enough to do so firsthand) at a wolverine romping through fresh powder: the thing looks downright overjoyed.
All things considered, we don't need to resort to that kind of anthropomorphism to define a close – heck, intrinsic – bond between the world's heftiest land weasel and the white stuff. As pioneering field biologist Adolph Murie put it, "The wolverine has indeed a kinship with winter."
This time of year, when its Northern Hemisphere haunts of tundra, taiga and mountain woods slumber under heaps of snow, the wolverine is sitting (or, rather, galumphing) pretty: sniffing out frozen animal carcasses, gobbling its own stowed-away meat caches and every so often taking down some living, breathing, snow-hampered prey.
In fact, winter gives the bushy-tailed mustelid (which also goes by "carcajou", "skunk bear" and "glutton") its most auspicious setup for actively preying on the hoofed mammals that are normally too quick for it. With its broad, snowshoe-like paws, the wolverine floats where animals like caribou and mountain sheep flounder. In such conditions, wolverines – normally scavengers and hunters of small game as well as newborn fawns or calves – may be able to catch and overpower prey that outweighs them many times over.
The snowpack is also an all-around larder for the wolverine: a readymade freezer for caching meat scraps, a candy shop of burrowed rodents to dig up and a hit-or-miss banquet table of carcasses – wolf leftovers, say, or creatures dashed and smothered in avalanches.
And it's not just the depths of winter. Snow continues to be a wolverine asset as the days lengthen and the temperatures rise.
Females claw out their dens in snowdrifts or within snow-buried rockpiles and other natural debris, often found in particular landscape settings such as avalanche chutes, forest deadfall or beaver lodges (which wolverines sometimes tear into to prey on the oversized rodents within). A spatial survey of North American and Scandinavian wolverine den sites showed more than 98 percent were located in areas with persistent snowpack.
Even after the animals abandon natal dens by May or so, growing kits may take refuge in snowpack rendezvous sites while mom makes her foraging rounds across the melting countryside.
The southern fringe of the wolverine's North American range turns narrow and patchy. Here, the species becomes a phantom of high, snow-socked mountains – partly because the wintry den sites it prefers are mostly restricted to lofty elevations.
But the giant weasels don't just hang around the heights during denning season. In southern Canada and the contiguous US, adult and juvenile wolverines of both sexes actually spend the bulk of their year in the kind of high country where kits are born and raised. Basically, research suggests that a long-lasting spring snowpack is a signifier of high-quality wolverine habitat year-round.
We once thought the scrawniness of wolverine turf here reflected the animals' need for deep wilderness far away from humans, but the ultimate reason may have more to do with habitat preference.
The historical record, for example, shows none of the weasels on the Great Plains. With its once massive numbers of bison, elk and pronghorn, the region would have offered a bounty of carrion – but the snowpack here tends to be limited during the full course of the wolverine's denning period.
Intriguingly, one study suggested that California's native wolverines were restricted to an island of suitably snowy high country in the southern Sierra, so naturally isolated from other North American populations that they were genetically closer to Eurasian wolverines. (Because the wolverines of the Sierra Nevada were killed off by the 1920s, the research relied on museum specimens for the DNA analysis.) At least one wolverine has lately recolonised California, but hair and scat analysis revealed the animal to be a disperser from the western fringe of the Rockies rather than a holdover of the original Sierra population.
There's no question, then, that the white stuff plays a crucial role in the wolverine's life history. And as biologists parse out just how crucial, the mustelid is emerging as another potential poster animal for the effects of climate change.
"If you want to take this a step farther, you might even be justified in thinking of Gulo gulo as the land-based equivalent of the better-known polar bear," writes naturalist Douglas Chadwick in The Wolverine Way.
What the sea ice is to the polar bear, this analogy suggests, a generous, long-lasting spring snowpack is to the wolverine.
As rising temperatures diminish both the depth and duration of mountain snow cover across the western US, research has identified a few potential refuges that should remain snowy long enough to meet the irascible weasel's needs: parts of southern British Columbia, the North Cascades of Washington, the "Crown of the Continent" country of northwestern Montana and the Greater Yellowstone Ecosystem.
"Overall, we expect wolverine habitat to persist throughout the species range at least for the first half of the 21st century, but populations will likely become smaller and more isolated," wrote the authors of that 2011 study.
Such projections have led conservationists in the US to lobby for better protections to help the species adjust to a shrinking range – by seeking snowy strongholds, for example, along protected habitat corridors.
In April last year, a judge in Montana overturned a 2014 decision by the US Fish and Wildlife Service not to list the wolverine as threatened, noting in her decision that the animal is a "snow-dependent species standing squarely in the path of climate change".
Of course, with Donald Trump (who once tweeted that global warming was a Chinese hoax) now in the White House, and the Endangered Species Act under attack, the outlook for animals like the wolverine looks bleaker. This sort of political environment may well change the playing field when it comes to giving the species more robust federal protection.
Meanwhile, biologists and volunteers across four states in the American West – Montana, Wyoming, Idaho and Washington – are currently collaborating on a monitoring project aimed at assessing wolverine distribution and minimum population, slated to run through April.
As Montana biologist Bob Inman told the Casper Star Tribune last fall, "There's been an extremely limited amount of information on the population not because they're not out there, it's because they're not that common. Anywhere the species exists is like finding a needle in a haystack."
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