The wolverine (Gulo gulo) is a powerful carnivore found in the high mountains, boreal forests, and arctic regions across the Northern Hemisphere. This species is one of the least understood mammals globally, maintaining a low population density across vast territories. While worldwide numbers appear stable, the wolverine’s presence in the contiguous United States is precarious. This difference between global abundance and the vulnerability of small, isolated U.S. populations has made its conservation status a subject of legal debate.
Defining the Wolverine’s Ecological Niche and Range
The wolverine is the largest terrestrial member of the weasel family (Mustelidae), characterized by a muscular build, broad paws, and a thick, dark coat. As an opportunistic scavenger and predator, it occupies an important role in cold environments, feeding on carrion or hunting small to mid-sized mammals. Its circumpolar distribution extends across the subarctic and alpine tundra of Alaska, Canada, and Eurasia.
In the contiguous U.S., the wolverine population is isolated, existing in a handful of high-elevation mountain ranges. These fragmented populations are found primarily in the Northern Rocky Mountains of Montana, Idaho, and Wyoming, and the Cascade Range of Washington and Oregon. The species’ survival is tied to cold climates and the presence of deep, persistent snowpack that lasts into the late spring, which is necessary for successful reproduction.
The Complex History of Legal Conservation Status
Globally, the International Union for Conservation of Nature (IUCN) lists the species as “Least Concern,” reflecting the large populations found in Canada and Alaska. This global assessment, however, does not account for the extreme vulnerability of the distinct population segment (DPS) residing south of the Canadian border. This small U.S. population has been the subject of a decades-long legal effort to secure protection under the U.S. Endangered Species Act (ESA).
The U.S. Fish and Wildlife Service (USFWS) first proposed listing the contiguous U.S. wolverine population as “Threatened” in 2013, based on the threat of climate change to its snow-dependent habitat. This proposal was withdrawn in 2020 after the agency concluded the threats were not as significant as initially believed. Conservation groups challenged this decision, and a federal court in Montana agreed in 2022, forcing the USFWS to reconsider the listing.
Following an updated scientific review, the USFWS issued a final rule in November 2023 listing the contiguous U.S. DPS as a “Threatened” species under the ESA. This designation acknowledges the severe threats faced by this isolated group, providing regulatory tools for its protection. The listing applies specifically to the genetically isolated group in the lower 48 states, not the broader North American population.
Primary Factors Driving Population Vulnerability
The primary ecological threat to the wolverine is the impact of a warming climate on its reproductive success. Female wolverines rely on deep, stable snowpack that persists into the spring, typically until mid-May, to excavate and insulate natal dens for their young, called kits. The snow drift provides a secure, thermally regulated environment that protects the vulnerable kits from predators and freezing temperatures. All known reproductive dens occur in areas with this persistent spring snow cover.
As global temperatures rise, the duration and depth of this necessary spring snowpack are diminishing across the western mountains. Loss of this denning habitat leads directly to reduced reproductive success and a decline in population viability. Modeling suggests that much of the current wolverine habitat in the contiguous U.S. could become unsuitable by the end of the century due to this climate-driven change.
This habitat loss is compounded by landscape fragmentation caused by human activity. Road networks, energy development, and winter recreation break up the expansive, connected landscapes wolverines require. These animals maintain very large home ranges and are sensitive to human disturbance. This disturbance creates “functional habitat loss,” leading to the genetic isolation of small populations and increasing their risk of local extinction.
Global and Regional Population Estimates
Estimating the total number of wolverines is challenging because they are naturally rare, solitary, and occupy remote, rugged terrain. Population densities can range widely, but northern populations in Alaska and Canada are extensive and considered secure, with the Canadian population estimated to be over 10,000 individuals.
In contrast, the isolated population in the contiguous United States is critically small, estimated to be fewer than 300 individuals. These small numbers are spread across several mountain ranges with limited connectivity. Researchers monitor this species using specialized techniques, including remote cameras and hair snares placed at bait stations to collect genetic material. DNA analysis of these samples allows scientists to identify individual animals and use spatial capture-recapture models to estimate density. These monitoring efforts provide the scientific data that informs conservation and legal status decisions.