A wolverine in wintry habitat. Photo courtesy National Oceanic and Atmospheric Association
by Todd Wilkinson
It's not easy being a wolverine in the so-called Anthropocene, described by scientists as the current geological age where human activity is the dominant influence on climate and the environment.
With only a few hundred wolverines left in the Lower 48, their survival is challenged by changing climate, landscape fragmentation brought by development and winter recreation (motorized, non motorized, backcountry, and industrial facilities like downhill and heavily used cross country ski resorts and trophy homes) displacing them from secure habitat.
Four-fifths of prime wolverine habitat in the Lower 48 is found on public lands. They are rare, have huge home ranges and exist at low densities. In 2013, a petition to have wolverines placed under protection of the Endangered Species Act as a threatened animal was posted in the Federal Register and it includes a bounty of of information about the natural history of the species. The US Fish and Wildlife Service issued a finding that listing was warranted but precluded because the agency did not believe cumulative effects posed a significant threat to the species' short-term persistence. State have opposed listing because they do not want any restrictions posed on resource extraction activities.
Many wolverine advocates, however, including some leading ecologists, believe the Fish and Wildlife Service in that decision refrained from listing for political reasons and did not take into account the magnitude of threats posed by warming temperatures, private development on the edge of public land and rising levels of outdoor recreation pressure that have grown since Covid.
Six years after the Fish and Wildlife Service published its finding, wildlife researcher Dr. Kim Heinemeyer was lead author of a study published in Ecosphere titled "Wolverines in winter: indirect habitat loss and functional responses to backcountry recreation." Their analysis examined the impacts of outdoor recreation on wolverines in primarily national forests of the Northern Rockies, including the Tetons. The study found that there are differences in how female and male wolverines respond to human disruption. Females exhibited more avoidance behavior to dispersed or off-road recreation.
Through her affiliation with Round River Conservation Studies, which has offices in Bozeman and Salt Lake City, Heinemeyer is considered a star of wolverine research. The study in Ecosphere has been widely cited in efforts being made to get wolverines federally protected, just like another species—the whitebark pine tree—also owed to threats posed by climate change. The study places a bead of scrutiny on outdoor recreation.
While some wolverine home ranges overlapped with areas in which outdoor recreation occurs, suggesting wolverines tolerate some level of human use, as intensity increases it can result in wolverines significantly changing their behavior.
Dr. Kim Heinemeyer, a leading wolverine researcher. The animal is sedated and part of her research. No, it is not ordinarily a good idea to approach or endeavor to handle wolverines that are wide awake. Photo courtesy Round River Conservation Studies
The authors wrote: "Wolverines displayed negative functional responses in habitat use as the intensity of both motorized and non-motorized winter recreation increased. [Animal] use of areas with motorized recreation decreased as the average intensity of motorized recreation increased within male and female home ranges...Similarly, both males and females showed negative functional responses to non-motorized winter recreation, even at the relatively low intensities of this recreation type. Habitat use of areas with non-motorized recreation declined as the availability of these areas increased within wolverines home ranges."
Last year (2020) another study, led by Mirjam Barrueto and including co-author Dr. Tony Clevenger who has been a pioneer in the study of wildlife overpasses and underpasses, examined impacts of humans on wolverines north of the US border. Clevenger is affiliated with The Western Transportation Institute at Montana State University in Bozeman.
In Canada, trapping of wolverines is still legal even though in 2018 wolverines were listed as an animal of special concern under the Species At Risk Act. The authors noted how protected areas, such as national parks, are not sufficient, by themselves, to support a stable population of wolverines. Similar conclusions have been found in the US for grizzly bears, wolves and ungulates.
"Ours is one of few studies globally to quantify long-term population trends for wolverine, filling a data gap that is common to other threatened species," the authors of the Canadian study wrote. "Although a large portion of our study area was formally protected, winter density and occupancy both declined by 39% over 10 years, and summer occupancy declined by 47% over 9 years. Wolverine density was 3 times higher inside versus outside protected areas, consistent with other studies in the region, reflecting differences in species and landscape management inside and outside protected areas and underscoring the importance of protected areas for wolverine conservation.. However, wolverine detection probability was negatively correlated with human development and with human activity, emphasizing potential detrimental effects of recreation activities, which are often concentrated within protected areas."
"Although a large portion of our study area was formally protected [inside national parks], winter density and occupancy both declined by 39% over10 years, and summer occupancy declined by 47% over 9 years. Wolverine density was 3 times higher inside versus outside protected areas." —Findings of the Canadian wolverine study that concluded national parks by themselves are not adequate to protect wolverines
They found, even in national parks, "several possible causal mechanisms exist that might link the high and increasing levels of recreation in our study area to the observed declines in density and occupancy of wolverines."
And they added, "Balancing outdoor recreation’s many positive aspects for humans with its increasingly evident negative impacts on species at risk will require careful collaborative management across departments and jurisdictions. Depressed population growth rates are particularly problematic for harvested species, as impacts quickly compound if harvest rates are not rapidly adjusted to account for negative trends in abundance and demographic rates."
In the wake of Heinemeyer study, the Winter Wildlands Alliance, which has been a major promotor of expanding outdoor recreation opportunities in the backcountry, shared its thoughts in a piece titled "Wolverines and Winter Rec: Sharing the Snow."
"Wolverines may use areas adjacent to popular winter recreation areas, and they may pass through areas with heavy recreation pressure, but they’re not sticking around in places where there are lots of people. In short, wolverines don’t den, rest, or eat in places that get a lot of backcountry ski or snowmobile use—even if those places are part of a larger wolverine home range. This is called 'functional habitat loss,' and it poses a real concern for wolverine survival."
The organization acknowledged that the conservation concern is two-fold. "First, wildlife biology 101 tells us that an animal's home range is the minimum amount of space that an individual requires to live and reproduce. If backcountry skiing and snowmobiling are effectively eliminating portions of a wolverine's home range, it's likely we're having a negative effect on that wolverine's ability to make a living and reproduce. And since wolverines are pretty rare, impacts to even a few individuals could have population-level impacts."
"Wildlife biology 101 tells us that an animal's home range is the minimum amount of space that an individual requires to live and reproduce. If backcountry skiing and snowmobiling are effectively eliminating portions of a wolverine's home range, it's likely we're having a negative effect on that wolverine's ability to make a living and reproduce. And since wolverines are pretty rare, impacts to even a few individuals could have population-level impacts." —Winter Wildlands Alliance
Secondly, the Alliance stated, "because of climate change, there are (and will continue to be) fewer and fewer places for all of us — skiers, snowmobilers, and wolverines — to find snow. Pair this loss of snow with a growing interest in backcountry snowsports and new tools and toys that help us travel deeper into the backcountry than ever before, and wolverines may have a tough time finding snowy places that aren’t overly impacted by humans."
The Alliance then added, "The good news is that with some self-imposed restraint we — the backcountry snowsports community — can help reduce our impact on these tough but vulnerable animals, without greatly impacting our own opportunities for fun and exploration in winter." Despite its promotion of self-restraint for the betterment of wildlife and a number of species besides wolverines, agencies like the Forest Service have admitted that illegal trespassing into closed areas has been a problem.
The Winter Wildlands Alliance likened the explosion of outdoor recreation to exurban development sprawl on private lands.
"We’re all familiar with the concept of suburban sprawl. Now think about your favorite backcountry area and how recreation use can sprawl across the landscape as people seek out the next untracked peak or meadow," the Alliance states. "By limiting that sprawl, we can limit the functional habitat loss that wolverines are experiencing."
This map from the US Fish and Wildlife Service shows, in dark green, areas where wolverines presented or recently have been found. Lighter green areas show habitat they could possibly re-inhabit but many optimistic projections are offset by the fact that snowpack levels, important to a wolverine's life history, have been decreasing over time.
Read this overview from the National Oceanic and Atmospheric Administration, one of the lead federal agencies involved with climate science, on the outlook for snowpack in the coming decades and how it relates specifically to wolverines. Click here to read the corresponding study. The best hope is that snowpack which lasts longer on north facing mountain slopes could still provide refugia for wolverines in the middle of this century.
The Greater Yellowstone Ecosystem with its abundance of public land and mountainous terrain holding snowpack is considered critical to any hopes that wolverines can endure in the coming decades of warming. One census of wolverines found just seven animals in Yellowstone. Scientists say that with dispersed populations of animals existed at low density, maintaining connections to other populations is critical.
"Because of climate change, there are (and will continue to be) fewer and fewer places for all of us — skiers, snowmobilers, and wolverines — to find snow. Pair this loss of snow with a growing interest in backcountry snowsports and new tools and toys that help us travel deeper into the backcountry than ever before, and wolverines may have a tough time finding snowy places that aren’t overly impacted by humans." —Winter Wildlands Alliance
"Because it has some of the largest and most contiguous patches of wolverine habitat in the conterminous United States, the Yellowstone ecosystem is likely to play an increasingly important role in the population dynamics and persistence of wolverine populations as the regional-scale of spring snow declines," Kerry Murphy, Jason Wilmot, Jeff Copeland, Dan Tylers and John Squires wrote in a scientific assessment titled "Wolverines in Yellowstone" that appeared in the journal Yellowstone Science12 years ago.
Are wolverines worth saving? If so, are human outdoor enthusiasts willing to alter their behavior and refrain from using areas that are important to the life history of wolverines?
Apart from those factors that will only continue to squeeze wolverine habitat, a huge threat is fur trapping, especially snares and leghold traps put out for wolves. Snares represent a major threat to grizzly bears, too, scientists say.
Unlike angling for trout, there is no catch and release. Consider this: because wolverines have huge home ranges, if just half of a mated pair is killed by a trap or even poison in some states put out for coyotes, you can destroy the short-term reproduction in a huge geographic area. While trapping for wolverines in prohibited in western states, the animals are highly vulnerable to being caught and killed accidentally.
Photo of wolverine shared on social media by Gaylene McHenry Lukenbill
In 2020, a wide range of conservation organizations petitioned the Fish and Wildlife Service again to to list wolverines, but the Service again rejected that action, though today it acknowledges that climate change causing range and habitat loss is the primary threat, coupled with a number of factors related to human land use.
Conservationists sued. Read this press release about the case in Montana that resulted a federal judge agreeing that the status of wolverines should be re-reviewed. "The wolverine deserves protection under the Endangered Species Act, and this is a step toward ensuring the species does not suffer additional harm before that happens,” said Amanda Galvan, associate attorney with Earthjustice’s Northern Rockies office. “The Fish and Wildlife Service previously ignored key studies that illustrate the threats the wolverine continues to face due to global warming. By reviewing a more complete picture of the species’ circumstances, we are hopeful that the agency will identify the need for increased protections.”
Groups represented by EarthJustice in the lawsuit are: the Center for Biological Diversity, Conservation Northwest, Defenders of Wildlife, Friends of the Clearwater, Idaho Conservation League, Jackson Hole Conservation Alliance, Klamath-Siskiyou Wildlands Center, Greater Yellowstone Coalition, Sierra Club and Rocky Mountain Wild. In light of the court decision, the Fish and Wildlife Service in late 2022 put out a request for new information on their biological status of wolverines. It is now considering new data submitted by conservationists and scientists.
Meanwhile, the latest 2023 session of the Montana legislature lawmakers are considering bills that would allow more liberalized use of snares to target wolves which biologists say poses a dire threat to wolverines. In addition, there is a bill that would make fur trapping a guaranteed right under the Montana Constitution making it more difficult to limit trapping in order to protect wildlife or ban it.
Today, the plight of wolverines is a concern shared globally across their arc of habitat in northern latitudes, notes a recent peer-reviewed study published in Global Ecology and Conservation. "Throughout wolverines’ range conservation strategies should encompass landscape protection from intensive development and human activity, restoring and maintaining connectivity of high-quality habitat, and climate change mitigation. These stressors are not limited to wolverines but are archetypal of stressors to biodiversity globally. Wolverines are more sensitive to these stressors, and as such are sentinels for change; conservation decisions for wolverines are likely the same to conserve vertebrate diversity across the northern Holarctic."
What do you think is the best way to protect the last 300 or so wolverines in the Lower 48? Drop us a note by clicking here and we may print your comment. Keep your thoughts on point and be respectful. Meanwhile, you can listen to a talk delivered by Dr. Kim Heidemeyer in Idaho and her research into the impacts of recreation on wolverines and after that enjoy a short video about wolverine research in Canada.
About Todd Wilkinson
Todd Wilkinson, founder of Mountain Journal, is author of the book Ripple Effects: How to Save Yellowstone and American's Most Iconic Wildlife Ecosystem. Wilkinson has been writing about Greater Yellowstone for 35 years and is a correspondent to publications ranging from National Geographic to The Guardian. He is author of several books on topics as diverse as scientific whistleblowers and Ted Turner, and a book about the harrowing story of Jackson Hole grizzly mother 399, the most famous bear in the world which features photographs by Thomas Mangelsen. For more information on Wilkinson, click here. (Photo by David J Swift).
