Savage. Fierce. Strong. Evil. Cunning.
The wolverine's reputation precedes it – as it has for generations.
In "Mark Trail's Book of Animals," Ed Dodd writes: "Savage ferocity combined with mischievous cunning has made the wolverine an object of hate and dread among trappers."
In "Mammals of North America," Vic Cahalane recounts the legendary prowess of the wolverine as fact: immensely strong and known to drive bears and mountain lions off their kills (two or three at a time, even); capable of taking down a bear in a fight; and bad-tempered loners that will destroy a cabin out of sheer deviltry.
Fact and fiction
Fish and Game researchers Howard Golden and Mike Harrington study the wolverines of Southcentral Alaska. In recent years they've captured 18 wolverines and equipped them with GPS tracking collars to better understand their movements and numbers. No doubt, wolverines are impressive, but their reputation is exaggerated.
"They've got such a bad rap," Harrington said. "I've had people ask, 'Will they chase you down? Aren't they dangerous?' People wonder if we're afraid of them," Golden said. "People attribute magic powers to them, but they're just doing their thing, looking for food. They are curious, smart animals and they figure stuff out pretty quick. They are smart enough to run down a trapline, and that'll make trappers mad. But it makes sense that they'd do that – there's always food on these traplines. They're not extra aggressive, they avoid trouble."
Wolverines are weasels, Golden said, and have the weasel nature. "That whole family is pretty similar, just the size is different. Ermine can be bold; weasels are an intelligent family of animals and they know how to survive."
While wolverines are usually solitary, the "bad tempered loner" stereotype gives the impression they are downright antisocial.
Not long ago, Golden visited a facility in Washington state that's home to about 40 wolverines. They shared a large common area, and he said they were quite tolerant and social with each other.
"If resources are limited, that can cause conflict, but they can be social," Golden said. "If food is plentiful, they've got no reason to worry about each other. We've seen them in April from the air wrestling and playing with each other, they weren't fighting, they're socializing."
They are territorial, in the general sense of the word, but Harrington and Golden use the term "home-use area" to describe terrain they favor. "They pick areas they maintain and keep to themselves. Males will overlap with females, but males don't overlap much with males, or females with females," Harrington said. "They need resources, and they pick an area where they can make a living and survive."
He said a wolverine can defend itself well, but it's no match for larger predators. "Two wolves can kill one," he said. "You hear stories about them chasing bears off, I've never seen that happen, or known anyone who has."
Their eyesight and hearing are not especially good, but they have an outstanding sense of smell.
"They've got a pretty good set of tools on them -- a really good nose, they can smell food over long distances or buried well under the snow," Golden said. "They can climb trees. They have a really warm coat. They've got strong claws for digging and defense, and incredibly strong jaws for biting and crushing bone and frozen meat -- not the same crushing power as a wolf, but they're not as big; a big wolverine is 40 pounds and small wolf is 60 pounds.
"You look at them, they're mostly built for scavenging," Golden said. "But they're very opportunistic and regularly kill small game. They're not as fast as wolves, and they don't work in packs, but they can be more predator than scavenger if the situation allows for it."
Wolverines hunt snowshoe hares and voles, and in summer ground squirrels and marmots are important prey items.
"We've got documentation of them killing smaller Dall sheep. In Scandinavian countries, they lose domestic sheep and reindeer to wolverines, and the government provides compensation to herders. The herders are required to hire rangers to document wolverine den sites and reproduction, and that's one reason they have great reproductive data."
It is true that wolverines are very strong for their size and have incredible stamina. Golden said a wolverine can cover 30 miles in a night, working a circuit in search of food. They will den up and rest for brief periods, and then get back on the move. That ability to travel through incredibly rugged mountainous terrain is not exaggerated.
"That's the big thing to come out of the GPS work for Mike and I, and it's pretty amazing when you see it," Golden said. "We get locations every 20 minutes. You can see how fast they move around terrain. They go up and down really steep, icy, rocky slopes like they're not even there. You could never hike it -- you'd need climbing gear. It's like they see the world as two-dimensional, the way they move up and down these snow-covered slopes."
Tracks in the snow
Wolverines behave differently from wolves, and they don't run in packs. An important difference is that a wolverine may sometimes sit tight for two or three days, in a den site or on a kill. Collaring and tracking wolverines has allowed researchers to learn a lot about wolverines in the process. Results from a cooperative study with Chugach National Forest indicated a wolverine density of 4.5 to five wolverines per 1,000 square kilometers in Kenai Mountains and Turnagain Arm area, which is typical for other areas of Southcentral.
"In some areas you're just looking for occupancy," Golden said. "Do we even have wolverines?"
The researchers pointed out two other methods used to study wolverines. Hair snares subtly snag a tuft of fur from a passing animal, and the DNA in the follicles enables biologists to identify individual animals, their gender and relatedness. Multiple samples over time can provide a population estimate. Photo identification uses remote, motion-triggered trail cameras to photograph animals in specific poses that reveal distinctive markings that can identify individuals -- much as tail fluke marks are used to identify humpback whales.
Catching wolverines: traps and darts
Researchers captured 18 wolverines between September 2007 and March 2014. Including recaptures, animals were live-trapped 14 times and darted from helicopters 10 times. Among the 18 wolverines captured were five juvenile females between ages 1 and 2, five adult females, four juvenile males and four adult males. Wolverines were captured in the Chugach Mountains east of Anchorage, on Joint Base Elmendorf-Richardson (JBER) and south of Anchorage in the Kenai Mountains. Capture work was done in cooperation with Chugach State Park, JBER Natural Resources Department and Chugach National Forest.
Three wolverines did not yield data – they likely slipped their collars right away. All telemetry work was done in late winter and early spring.
Cameras proved to be a valuable tool for trapping and darting. Motion-triggered trail cameras were set up near the live traps, and researchers wore helmet-mounted video cameras when helicopter darting to help them learn from capture attempts.
Darting can be efficient under ideal conditions, and Golden said one day they caught four wolverines. That was exceptional; others days they spotted wolverines they couldn't catch. Aircraft searched for roaming wolverines and then called the capture team.
"Wolverines are never very abundant, even when they're abundant for the species," Golden said. "You need good conditions to track them. We had two fixed-wing aircraft just looking for animals, sometimes for hours, and then we're sitting on a ridge with the helicopter, waiting. We get the call and go after them."
Darting a moving animal from a moving helicopter is challenging, particularly when the target is a small animal moving in mountainous terrain. But one thing played to the scientists' advantage. When pursued, wolverines tended to run uphill. In deep snow that hampers their speed.
"On hard-packed snow, we couldn't believe how fast they can run," he said.
Pursuit was limited to 10 minutes. "Sometimes we had to say, 'We're not going to get this guy.' "
Once caught, wolverines were quickly processed as biologists monitored temperature, heart rate and respiration. They took tissue samples (for DNA), hair and blood. The animals were weighed and measured, age estimated, marked with an ear tag and equipped with a GPS collar.
The collars were programmed to record locations at 20-minute intervals, maintaining that rate of data collection for about three months. Collars also stored altitude and air temperature data.
Two types of GPS collars were used. Both stored thousands of location data points and allowed remote downloading of collar data. One model could be released remotely to drop off; the other could not and required recapture to retrieve collars.
Golden and Harrington had some success live-trapping on JBER during the first two or three years of the project, while new animals were still coming to the trapsites. Researchers took advantage of a winter moose hunting season on JBER that attracted wolverines to kill sites. However, it became difficult to attract wolverines into traps last winter, which they attributed mostly to a lack of new wolverines visiting the area. From images gathered on remote cameras, the animals appeared too wary to be caught.
"They remember where they've found food, but they got wise to the traps really quick," Harrington said. "They're hard to live trap in the first place, and really hard after that. You might fool them once, but how do you fool them again after that? We got creative with different kinds of bait -- we tried chickens wrapped in bacon, and big wads of beef suet."
Wide ranging
Home range estimates for wolverines in Southcentral Alaska show females use 115 to 230 square miles and males use 270 to 380.
Males and females traveled extensively throughout their home areas. Both sexes occasionally went on exploratory trips before returning to their primary areas. A look at the movements of five wolverines over the course of a year (two females and three males) showed great variation in distances traveled, some days they covered a lot of ground, others days not so much. The average distances traveled per day was about 7 miles for females, and about 13 miles for males.
"One male had twice as big an area as other wolverines," Golden said. "It may be that area had lost a male and this animal just took over the whole area, at least for the short time the collar was active."
Because the focus of the study was movement in late winter and spring, the researchers did not track wolverines year-round.
"They do spend a lot of time in summer during the breeding season testing boundaries and trying to encounter females," he said.
An important time in a wolverine's life is when a young adult strikes out to establish its own home range. Wolverines are born in February or March, two to four kits that usually dwindle from mortality to one or two by fall.
"Mortality is pretty high for kits," Golden said. "We're finding females generally don't have a litter before they're about 3 years old, and then typically have a litter about every other year."
The kits are essentially full grown by October or November and begin moving out. It can be tough for a young wolverine to find a territory that is unoccupied and suitable. "A daughter might stay with mom a couple years and inherit her area," Golden said. "Young may try and stay relatively close to their natal area, and siblings may be more tolerant of each other."
But wolverines have been known to disperse as far as 235 miles. Dispersal is important; that's how wild areas that "produce" wolverines can supply them to potential home ranges elsewhere, good habitat where wolverines may have been harvested.
That balance is a model for sustainable yield -- a refuge from human activity, good habitat for wolverines that are producing young that will emigrate out.
Hunters and trappers in Alaska harvest about 550 wolverines each year. Because wolverine reproductive potential and survivorship is low it's important to understand where and when animals are harvested to be sure the population is not overharvested. Wolverines disperse depending on availability of food and habitat resources, and animals dispersing from areas where they are not trapped replenish the population in areas where they are hunted and trapped.
Riley Woodford is the editor of Alaska Fish and Wildlife News, a publication of the Alaska Department of Fish and Game.