Creature Feature: Wandering Wolverines

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Wolverines are an intriguing species, but can they survive climate change?/NPS

Is that a black bear cub? A badger? No, it’s a wolverine!

Wolverines have distinct color patterns on their face, neck, and chest making each individual animal unique.

Though their appearance leads most to believe them to be a relative of bears -- indeed, the Blackfeet Indians referred to them as "skunk bears" -- they are the largest members of the weasel (mustelidae) family that exclusively live on land. Other omnivorous mammals like otters, badgers, and minks also belong to this family, yet the wolverine in comparison lives quite a different lifestyle than its relatives.

All In The Good Looks

The typical wild male wolverine can weigh anywhere from 20-55 pounds, with exceptionally large males reaching 70+ pounds. They stand about 16 inches tall, and can range up to 44 inches from nose to tail. Female wolverines are significantly smaller, tipping the scales at at 15-26 pounds while standing about 14 inches tall. Despite the size difference, both male and females have an average life span of 7-12 years.

Wolverines have a stocky and powerful muscular build, and a broad, round head that houses a short snout and forceful jaw. Between their aggressive, persistent personality and their bone-cracking jaw, wolverines are able to tear through frozen meat and with ease. Like other mustelids, they have a unique pair of molars in the back of their mouths that are rotated inward 90 degrees. This arrangement makes it much easier for them to tear chunks of meat from prey, even when the victim is frozen solid. While other mammals pack on the pounds in preparation for hibernation during the cold winter months, wolverines are well equipped for the coldest season. They have thick, dense fur, and wide, five-toed webbed paws that enable them to run on powdery snow effortlessly.

What’s For Dinner?

Wolverines are what some would call resourceful feeders that tend to munch on of a variety of food depending on what they can find or kill. They capture and feast on smaller mammals, such as ground squirrels and rodents, but can also kill preys much larger than themselves when conditions are in their favor (think moose or caribou). Wolverines, more often than killing, drag away the remains of animals attacked by other predators to a new location for scavenging. Wolverines even use freezers, natural freezers of course, by stashing kills in icy slits or under rocks for scarce times. What about summer months? These opportunistic feeders are no stranger to chomping on berries, snagging eggs, or even eating the occasional plant.

Give ‘Em Some Space

Unlike many other animals in chilly climates, wolverines are active year-round. Males are fiercely territorial and need plenty of room to roam. They are known to travel great distances, as much as 18 miles in one night. Females are more than welcome within the scent-marked territories of male wolverines, which can span up to 300 miles, yet most males keep their distance from one another. Because of their thick skin and tough build, they can maneuver up, down, and all around mountains, trees, cliffs… you name it. Although these furry mammals seem like the inverted social type while solo scavenging, male wolverines are surprisingly social with their kits. Some males continue to interact with them even after they leave the cozy confines of mother's care.

Wolverines have been spotted in Denali National Park, Yosemite National Park, Yellowstone National Park, Glacier National Park, and North Cascades National Park among others. It’s difficult to say just how many wolverines are wandering around the parks. Their extensive travels, sneaky scavenger-like maneuvering, and solo dwelling make it difficult for researchers to closely monitor their patterns.

The Mating Game

In late spring to early summer, wolverines mate with more than one partner during the breeding season. In fact, because of delayed implantation, some littermates may have different fathers. The egg is fertilized after mating, but development is temporarily paused in the uterus before implanting, which happens four to six months later. Though it sounds a bit strange, this method of delayed implantation works to their advantage. It allows wolverines to birth, and raise young kits when food and survival are lower on the list of concerns. Wolverines are in tune with not only the climate, but also the food supply around them. In some cases, they will forgo breeding when food supplies are lacking. Talk about an effective approach to reproduction!

Pregnant females are found in deep snow dens. The dens usually consist of an intricate web of snow tunnels near noticeable boulders, uprooted trees, and avalanche debris. Pups are born 30 to 40 days after implantation, usually in late May. Litter sizes vary anywhere from 1 to 6 pups, with the average around 2 or 3. Just like Dalmatian puppy dogs, wolverines are born as white as snow. Kits grow fairly quickly reaching the size of an adult by early winter, but they accompany their mothers and siblings until they reach full maturity for two to three years.

Can They Survive?

Because they live at high altitudes, and rely on snowfields for denning, concern has been voiced over whether wolverines can survive in the warming climate. These opportunistic carnivores -- they are known to scour avalanche chutes for animals killed in slides -- once roamed wide and far across the continental United States. Historical populations were found in the coastal mountains of California, Oregon, and Washington, and they roamed the Rocky Mountains from Glacier National Park on the Canadian border all the way south to Taos, New Mexico, east into the Great Lakes region, and even in the Northeast.

While the U.S. Fish and Wildlife Service had considered listing the animal as a threatened species, earlier this month the agency reversed itself. The director of the agency's Mountain-Prairie Region, which includes Wyoming and Montana, Noreen Walsh, decided there wasn't enough evidence to demonstrate climate change was adversely affecting the species, according to a story in the Los Angeles Times. That development led other biologists outside Fish and Wildlife to speculate that politics, not science, had forced that decision.