Winter’s warrior: the wolverine is as fragile as it is fierce

Wolverine in snow
With large home ranges and unique traits to thrive in snow, wolverines embody nature's need for connected ecosystems that allow wildlife to move and adapt.

By Kayla Heinze, Communications Specialist

Picture for a moment, what it is like to be a deer in winter. Towering evergreens bend low with the weight of accumulated snow and you find yourself fighting gravity to extract your leg from its depths. Post-holing slowly forward, this ungraceful movement makes you vulnerable to a cunning and lurking predator who does not just survive, but thrives, in winter conditions like these. 

The wolverine, Gulo gulo, uses the snowpack to its advantage. The largest land-dwelling member of the weasel family, wolverines are still a relatively small mammal weighing roughly between 20 and 40 pounds. Equivalent to a large cat or small dog, a lone wolverine can take down prey such as deer, elk, and caribou (well over 10 times their size) with only the snow as an aid. 

Wolverines’ relationship with snow is extensive. From dens for their young to caches for food storage, wolverines’ reliance on winter distinguishes them as both a remarkable and sensitive creature. With grizzlies soundly resting the cold months away, winter is a great time to highlight other standouts from the biodiverse community of the Northern Rockies. (Follow Vital Ground on Instagram and Facebook to catch our month-long series about the umbrella effect of grizzlies, or head deep into the blog archives to read about previous years’ winter wildlife focal species.)

Wolverines: at home in the snow

Wolverine
Wolverines are fierce predators but as a snow-dependent species their long-term survival in the Lower 48 is fragile. (Photo by Zoofanatic on Flickr)

While bears deal with the seasonality of their environments by dropping their heartbeat and going dormant, wolverines have evolved to maintain high levels of activity in winter. Their wide paws act like a snowshoe, allowing them to skim over powder and easily overcome their slothful prey. Frost that forms on their fur falls away, keeping them dry and warm. This adaptation has made them a prized target of fur trappers, though the mechanics of their frost-repellant fur remain mostly a mystery

For many other species, winter is a brutal season. Wolverines conquer this oft-overlooked niche, making the most of other animals’ struggles in sparse times. As a result, they have earned a mythical reputation as a “demon of destruction.” But as naturalist author and Vital Ground trustee Douglas Chadwick explores in his book “The Wolverine Way”, the animal is even more complex and remarkable in reality than in legend. 

One instance that displays both the wolverine’s affinity for snow and its intelligence is caching behavior. Wolverines will stash recent kills and scavenged carrion under the snow for refrigeration and safe-keeping. Dens are also made in high-altitude, deep snow conditions. Relying again on the insulation and protection offered by layers of packed powder, mothers will dig tunnels (up to 60 yards long!) and give birth inside them during the late winter months. The wolverine’s snowy haunts stay wintry long after the calendar has turned to spring: At 86 percent of wolverine den sites surveyed by one study in Idaho and Montana, snowpack lasted, sometimes with significant depths, until late May. 

This intense and all-encompassing reliance on snow, threatened by unstable environmental conditions, has led Chadwick to designate the wolverine as, “the land equivalent of the polar bear.”

Warming winters

According to the U.S. Fish and Wildlife Service, wolverines in the Lower 48 need at least 5 feet of “persistent and stable” snowpack for their natal dens. The guarantee of this minimum is becoming increasingly uncertain as global warming adds chaos to winter weather conditions. 

Winters worldwide are getting hotter on average. In parts of the wolverine’s range, spring snowpack is melting earlier. This could leave young wolverines, who are typically born between February and April, exposed to the elements and predators when they are at their most vulnerable. For a species with naturally low reproductive rates that also uses snow as a hunting tool, inconsistent and declining snow levels could spell serious trouble.

The Washington Department of Fish and Game lists the species as being highly vulnerable to climate change. In Montana, one of only five states in the Lower 48 where wolverines currently reside, the Department of Fish, Wildlife and Parks considers them a species of concern. 

It seems certain that the coming decades of winters, both more mild and more unpredictable than we are used to, will impact this creature who has long evolved to flourish where others falter. 

While we wait to see what happens with future snowfall, a current controversy is accumulating over the wolverine’s federal listing status under the Endangered Species Act (ESA). A 2020 decision by the U.S. Fish and Wildlife Service (USFWS) opted not to list the species, citing connectivity with larger Canadian populations. Wildlife advocacy groups pushed back, saying trapping near the border has created an impasse, effectively separating the transboundary populations. 

The following years have seen a series of lawsuits and appeals. A temporary ruling will protect the species under the ESA until this coming November, when the USFWS will be required to announce its new decision.  

Birthing new hope

Joni the wolverine and kits
A remote camera shows the wolverine nicknamed Joni with her first pair of kits in 2020. (Photo courtesy of Mt. Rainier National Park and Cascades Carnivore Project.)

Warming weather trends, erratic snowfall, and a precarious protection status reveal that wolverines are more fragile as a species than legend makes them out to be. But hope is far from lost. The species has, after all, faced hard times before.

In a similar history to grizzlies, these weaselly predators were driven close to extinction in Montana during the early 1900s. That magic fur we discussed earlier, and their fear-inspiring powers, led to widespread overharvesting and intentional killing of wolverines. But the budding conservation movement made the same state the site of their recovery. 

Successful habitat protection and trapping regulations allowed wolverines to increase their populations and spread back into Washington, Idaho, Wyoming and Oregon. As they face new threats, Vital Ground’s work to increase large-scale landscape connectivity will help them maintain this positive trajectory. 

Like bears, wolverines have large home ranges. Males in Montana have been documented with ranges up to 162 square miles, and females up to 149 square miles. Committed conservationists like you enabled valuable habitat connectivity projects last year, creating linkages that may help wandering wolverines move to snowy holdouts more safely as they adapt to warming winters.

Meanwhile, signs of resilience are already emerging from the snowpack. Last summer, Washington’s most famous wolverine, nicknamed Joni after she became the first wolverine mom on Mt. Rainier in at least 100 years, was sighted with two kits for the third year in a row. This rare occurrence exemplifies the tenacious spirit of wolverines, who demonstrate how bleak seasons can bring out our strength and ingenuity.

Fragile as they may be, these warriors of winter will not go down without a fight. 

Learn about other wildlife that benefit from landscape connectivity…

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