Wolverines appear throughout American pop culture. Superheroes and sports teams share their name, and it’s little wonder why. These creatures have a reputation for being fierce and strong, which makes for a great mascot or comic book character. When it comes to spotting a wolverine, though, you’re more likely to see a pop-culture reference than to see one in person. Not only are they fierce, they’re incredibly elusive.
Wolverines in Wyoming live at high elevations in rough terrain. This, combined with limited numbers in the Cowboy State, makes it difficult to spot a wolverine. Even if you’re actively searching for one, the chances of finding a wolverine in Wyoming are low.
This elusive nature makes wolverines difficult to study, too. Through a collaborative effort, researchers in multiple states have worked together to learn more about how many wolverines are present and what their distribution looks like. While sports fans are studying the chances of wolverine teams and players, researchers are studying wolverines in the field.
The drive to thrive
Wolverines live in the northern reaches of our planet, from the Arctic at their northern extent and the Greater Yellowstone region of Wyoming toward the southern extent of their range. They can be found in North America, Europe and Asia. In the lower 48, they primarily live in high-altitude forests with rugged terrain that experience winter conditions late into spring. The climates they experience can be a hard place to call home, especially in the winter. Through physical and behavioral adaptations, they have become well-adapted to their environment.
"Their hides are thick and their fur is dense to withstand cold temperatures,” said Heather O’Brien, Game and Fish nongame mammal biologist. “Their feet are large allowing them easy travel across deep snow, and their neck and jaws are strong, giving them the ability to crush bones and eat frozen meat from carrion they have cached under the snow."
Their long, brown fur is also water-resistant, allowing them to maintain their body temperature even when wet. They are short and stocky, about the height of a beagle, and weigh between 17-40 pounds. Their short stature makes them good at fitting into and living in dens.
In the winter, wolverines stay at high elevations. They use their unique adaptations to acquire food despite the harsh conditions. Staying at high elevations allows them to avoid competition with large predators that move to lower elevations or are inactive in the winter. When it comes to finding food, wolverines take advantage of the opportunities in front of them. They hunt and scavenge for food, and are known to eat more than 20 animal species as their diet shifts throughout the year. Their keen sense of smell helps them find food. Throughout the winter, they often eat dead deer and elk carcasses. In the summer, a greater variety of food is available, and they eat whatever is around including small mammals, bird eggs and berries. Wolverines also are known to hide food to eat when food supplies are low.
Wolverines have huge home ranges, allowing them more space to find food in the winter. Female home ranges can stretch up to 113 square miles, and male home ranges are even more expansive. Their home range includes a variety of habitats including forest edges and riparian areas. Females’ home ranges include good sites to build dens, like talus fields. Wolverines move within their home range during the year, driven by weather and food. Since their home ranges are large and wolverines are solitary, their population isn’t very dense.
Wolverines mate throughout the summer. Females experience delayed implantation, meaning the pregnancy can be paused until the proper time. They wait to continue the pregnancy until closer to the winter months and give birth in dens between January and April. In Wyoming, most females give birth to one to four kits in a season and often do not rear young every year. Wolverines grow quickly, but they do not leave their mothers for a year, slowing their reproduction rate when compared to many other mammals.
Biologists wanted to learn more about the distribution of the species in the lower 48. In 2016, researchers from Idaho, Montana, Washington and Wyoming set out to learn more about where wolverines can be found in the lower 48 and how many. Studying an animal this elusive was a challenge, but they worked together to create a study that overcame the many difficulties presented by the species.
The work
The team of biologists started by considering wolverine behavior, habitat and adaptations. Wolverines typically live in areas with steep terrain, snow cover that lasts late into the spring and tend to live at elevations above 8,500 feet. In Wyoming, that allowed them to narrow their study to a few potential locations: the Greater Yellowstone Ecosystem, Absaroka, Wind River and Wyoming ranges along with the Medicine Bow and Bighorn mountains.
After narrowing in on some key areas, biologists broke them into smaller sections. For this study, the biologists defined the study units to replicate the size of a female’s home range. This allowed the area to be large without the potential of missing a wolverine’s range completely.
Studying each unit isn’t possible, but biologists can survey random units and apply those results to the entire study area. Using computer models, they mapped all the study units and randomly selected which ones to survey.
Researchers next had to find the wolverines. With a low population density, visually surveying for them wouldn’t be very successful. Instead, researchers used the wolverine’s opportunistic feeding to their advantage. Researchers placed attractants to lure the wolverines to a single point or station set up within each of the selected study units. At each station, they installed a camera trap facing a lure tree.
There were two possible configurations for attractants based on how accessible the sites were to biologists. At more accessible sites, the tree had a large piece of carrion as bait. In locations biologists could not access regularly, the tree had a dispenser that periodically released a smelly liquid to attract wolverines. Both configurations included a wire brush to collect hair samples for DNA analysis.
Having bait and lures in the wild could attract other predators as well. To minimize this, researchers play to the wolverine’s adaptations for high-altitude winter survival. Placing and monitoring lures during the winter created challenges for researchers, but ultimately increased the chance of bringing in wolverines without drawing in other predators that are inactive or at lower elevations.
Researchers conducted wolverine studies in 2016-17 and 2021-22, and they plan to repeat them every five years to track trends and changes in wolverine populations.
Emerging results
During the 2016-17 study, researchers monitored stations in 183 study units from December until March. This included the Greater Yellowstone Ecosystem and the Bighorn Mountains in Wyoming. In 2021-22, they expanded the area to include the Medicine Bow Mountains. The second study also added study areas in California, Colorado, Oregon and Utah.
The results from the 2016-17 study were interesting. Across Montana, Idaho, Washington and Wyoming, 59 of the 183 survey units detected wolverines. From these results, biologists could estimate that of the 633 total units, 268 were likely used by wolverines. Of the 51 study units in Wyoming, six detected wolverines. Of Wyoming’s 153 total survey units, the team estimated wolverines occupied approximately 24. In the 2021-22 study, the units where wolverines were detected increased in Wyoming. Of Wyoming’s 49 study units selected for that survey, 13 detected wolverines.
“The increase in wolverine occupancy in Wyoming between survey periods could be the result of increased colonization in the state, ongoing reproductive success, or it could be due in part to improved techniques as field personnel perfect survey methodology,” O’Brien said.
In addition to the camera traps, biologists collected DNA from wolverines by catching hair from the wire brushes. In 2016-17, the entire multistate study collected 145 samples submitted for genetic analysis. Results showed the samples came from 26 unique females and 24 unique males. In Wyoming, four unique individuals were identified, two males and two females. One of the females represented the southernmost identified female in the U.S. The 2021-22 study identified 10 individuals in Wyoming, six males and four females. There are likely more wolverines in the state, even if researchers haven’t collected the DNA of each animal.
The results of this study give a glimpse into what wolverines in the lower 48 and Wyoming are doing. We know they are returning to Wyoming after being nearly eliminated in the contiguous U.S. in the 1920s. They are active in much of the Greater Yellowstone Ecosystem, including the Wind River Range and the Absaroka Mountains.
"Results from these studies help us to track changes over time in wolverine distribution, and can be used to make more informed decisions about the status and management of this elusive species,” O’Brien said.
The public has long been fascinated with wolverines. This interest has permeated into pop culture and even into sports. Even as wolverines take their place on the big screen, researchers continue to learn more about the species throughout the American West.