A mid-size carnivore in the weasel family, the wolverine (Gulo gulo) is active throughout the year in cold, snowy environments to which it is well adapted. Its circumpolar distribution extends south to mountainous areas of the western United States, including the greater Yellowstone area where they use high-elevation islands of boreal (forest) and alpine (tundra) habitat. Wolverines have low reproductive rates, and their ability to disperse among these islands is critical to the population’s viability. Climate-change models predict that by 2050, the spring snowpack needed for wolverine denning and hunting will be limited to portions of the southern Rocky Mountains, the Sierra Nevada range, and greater Yellowstone, of which only the latter currently has a population. Wolverines are so rarely seen and inhabit such remote terrain at low densities that assessing population trends is difficult and sudden declines could go unnoticed for years.
Commercial trapping and predator control efforts substantially reduced wolverine distribution in the lower 48 states by the 1930s. Some population recovery has occurred, but the species has not been documented recently in major portions of its historic range. In the Greater Yellowstone Area, wolverines have been studied using live traps, telemetry, and aerial surveys. A group sponsored by the Wildlife Conservation Society has documented ranges that extend into Yellowstone National Park along the northwest and southwest boundary. A second group, which included researchers from the National Park Service, the US Forest Service, and the Northern Rockies Conservation Cooperative, which surveyed the eastern part of the park and adjoin- ing national forest from 2006 to 2009, documented seven wolverines. The average annual range for the two monitored females was 172 mi2 (447 km2); for three males, 350 mi2 (908 km2). The other two males, both originally captured by the Wildlife Conservation Society, dispersed from west and south of the park: M557 established a home range north of the park in 2009; M556 became the first confirmed wolverine in Colorado in 90 years. But to create a breeding population there, he will need to find a female.
Wolverine populations in the US Rockies are likely to be genetically interdependent. Even at full capacity, wolverine habitat in the Yellowstone area would support too few females to maintain viability without genetic exchange with peripheral populations. The rugged terrain that comprises a single wolverine home range often overlaps several land management jurisdictions. Collaborative conservation strategies developed across multiple states and jurisdictions are therefore necessary for the persistence of wolverines in the continental United States.
In August 2014, the United States Fish and Wildlife Service withdrew a proposed rule to list the wolverine as a threatened species under the Endangered Species Act in the contiguous United States. In spring of 2016, a US District court reinstated the proposal ruled that it shall be conferenced on as necessary until a final proposed.
Climate change impacts on wolverine habitat, specifically the likelihood of declining habitat in high elevation snowpack for denning females, had been identified as a chief threat to this species. In Montana, which has the largest wolverine population of the lower 48 states, an annual quota of 5 wolverines were available for harvest by licensed trappers in recent years.
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U.S. Fish & Wildlife Service (2014) Endangered and Threatened Wildlife and Plants; Threatened Status for the Distinct Population Segment of the North American Wolverine Occurring in the Contiguous United States; Establishment of a Nonessential Experimental Population of the North American Wolverine in Colorado, Wyoming, and New Mexico Federal Register, 79,47522–47545.
Last updated: June 24, 2020