Move over Logan — real wolverines don’t need adamantium implants to be the kickass, socially-withdrawn lords of the North.
The wolverine is the largest living member of the mustelid family, with males weighing in at around as much as 18 kilograms. Despite its hulking, bear-like appearance, wolverines are closely related to other members of the weasel family, such as ermines, martens and fishers. Living primarily in boreal forests, wolverines often have to compete with larger predators, such as wolves and grizzlies, which has lead the wolverine to a rather novel survival strategy — wait for someone else to kill something and then take it from them.
Wolverines are primarily scavengers, says Thomas Jung, a senior biologist with Environment Yukon. Their appetite is legendary and their scientific name, gulo gulo, comes from the Latin word for “glutton.” While they are not the most efficient hunters — lacking the stealth of a lynx, the size of a bear, or the speed and cooperative abilities of wolves, for example — they make up for it in their ability to find and devour carrion, swallowing everything down to the very last bit of hoof or hair. They have short, powerful muzzles with a strong bite force that are “made to crunch on things,” says Jung.
“Frozen bones are really hard to break open,” says Jung. “Their jaws allow them to break into those and just crunch them up.”
Moreover, wolverines are out foraging for food “in the bitter cold while bears hibernate,” Jung says.
Owing to their solitary (and rather unfriendly) nature and the remoteness of their environment, wolverines are notoriously difficult to study, and are very rarely seen by humans, even experienced bushfolk. There are many anecdotal stories, however, of trappers and hunters observing them taking down full-grown moose — an animal approximately 28 times their own weight. Similar stories have been told of enterprising wolverines who will attack and scare off grizzly bears from their kills.
While difficult to validate, these stories “seem to be pretty true … based on an accumulation of observation,” Jung says.
“Nothing seems to get in their way and nothing seem to faze them…. They don’t seem to back down from anything. They are kind of the badasses of the wild places in the Yukon.”
In addition to their unsurpassed tenacity and bite strength, wolverines are equipped with large, hooked claws (Marvel Comics got a few things right, after all) which wolverines basically use like mountaineering boots, traversing up and down near-impossible terrain and sometimes straight up the sides of mountains. They have very large paws which act like snowshoes, allowing them to move efficiently and quickly through deep snow, and their short, stocky legs and small, rounded ears minimize heat loss. Their fur is extremely thick and resists frost and is highly valued by trappers, particularly for parka trim.
An avalanche, Jung says, is essentially a smorgasbord for wolverines, who patrol the aftermath for less fortunate animals. They use their large paws and hooked claws like shovels to dig the carcasses out and devour them.
Perhaps surprisingly, wolverines are very good parents, Jung says. Males have large territories which overlap those of two to three females, all of which he mates with. This sort of sexual courtship and selection by proximity is not uncommon — the tough-yet-cuddly pika employs a similar strategy — but what makes the male wolverine unusual is that his interest does not end after mating season. Instead, males will continue visiting their mates and the resulting litters in a kind of paternal timeshare arrangement, investing considerable energy in their offspring, which are called kits, Jung says.
“They’re actually very social, with good family tendencies,” he says. “They spend time just teaching young wolverines how to be wolverines…. It’s a bit unexpected.”
Males have well established ranges, and, due to their low population density, rarely encounter each other, making male-on-male aggression relatively low for such a powerful and territorial animal.
“They have their territories and other males respect that,” says Jung.
The breeding season and how wolverines pair and have litters is something that biologists are still learning about, but in the Yukon they seem to prefer to breed in late summer or early fall, Jung says. However, female wolverines delay their own pregnancies with an adaption called “delayed implantation,” a trait found in some other mustelids. Essentially, if the female does not have enough body fat and reserves by winter, her eggs don’t implant, effectively preventing the pregnancy before it can begin.
“It’s a really unique thing,” Jung says. “Basically, her body says ‘yes, the conditions are good, we can support a litter, we have the energy,’ or she doesn’t have the litter.”
If the pregnancy is successful, wolverine kits are typically born in late February to mid-April, with relatively small litters of between two and four. A female can begin breeding at around three years of age and is usually finished her reproductive life at around nine years of age, with both males and females living up to 13 years in the wild.
The Yukon boasts one of the largest, densest populations of wolverines in the world, with an estimated 5,000 to 7,000 individuals, roughly the same population as grizzly bears. However, they are listed as vulnerable in the Yukon. In the lower 48 states, and parts of Russia and Scandinavia, the wolverine population has plummeted over the last several decades, even disappearing from some traditional ranges in the northeastern United States. Exactly why isn’t known, but wolverines are “extremely sensitive and avoid areas where humans are present,” Jung says.
In some places the wolverine does seem to be making a comeback, Jung adds, noting that just this year, a wolverine was spotted in Michigan for the first time in 250 years. Whether that indicates a returning native population there is unknown, however, because wolverines can range over huge distances and the animal could just have been passing through.
The species “seems to be doing just fine” in the Yukon and northern British Columbia based on trapper harvest reports, he says.
“In the Yukon, we have a high density of wolverines because we have the types of things wolverines like — limited human development, rugged terrain, and the kinds of prey wolverines prefer to eat,” he says.
Jung describes this rarely-seen, difficult-to-study animal as having “something mythical about them.”
“They’re rare and something people don’t forget after they’ve seen one,” says Jung. “I even get excited just to see a (wolverine) track.
“They’re the true essence of the wilderness.”
Contact Lori Fox at firstname.lastname@example.org