Increased Threats to Wolverine Identified in Latest U.S. Fish and Wildlife Service Report

An update to the 2018 Species Status Assessment may provide justification to list the animal under the Endangered Species Act

By Micah Drew

For decades the U.S. Fish and Wildlife Service (FWS) has waffled over whether threats to wolverines warrant listing the elusive mammal under the Endangered Species Act (ESA). But a new report published in September may help the species receive federal protection after identifying stressors, including climate change, that will continue to negatively impact the wolverine’s long-term vitality.

In a 70-page addendum to the 2018 Species Status Assessment (SSA) of the wolverine, the FWS reversed several conclusions that were previously cited as a reason to deny the wolverine a place on the ESA.

“Core wolverine habitats are projected to become smaller and more fragmented in the future as the result of climate change and human disturbance,” according to the report, which reviewed more than 180 publications from the intervening years as well as hundreds of new wolverine observation records. “Overall, future wolverine populations in the contiguous U.S. may be less secure than we described in our 2018 SSA.”

The FWS has gone back and forth on whether to list the wolverine under the ESA due to contradictory evidence of threats to the species as well as opposing priorities by federal administrations. In 2013, citing the impacts of climate change on wolverine habitat, the FWS proposed the population of wolverines in the Lower 48 receive threatened status under the ESA. But the agency reversed course a year later citing inconclusive science and prompting conservation groups to file a lawsuit.

In 2016, U.S. District Judge Dana Christensen reinstated the proposed listing, instructing the agency to take action “at the earliest possible, defensible point in time.” Despite the judicial order, no action was taken and in October 2020, FWS reasserted its decision not to list the species “finding that the loss of wolverine habitat due to climate change and other stressors was not as significant” as previously thought. 

More legal action ensued in 2022, and Montana U.S. District Judge Donald Molloy gave FWS an 18-month window to reassess its 2020 decision, which will include drawing on the addendum published in September.

The latest report indicates that the species may have limited ability to “adapt and persist in the face of projected environmental change,” citing both climate change effects on snowpack and alpine habitats and increases in human development throughout wolverine territories.

Wolverines in the contiguous U.S. are concentrated in five key regions, which include the Greater Continental Divide Ecosystem, centered around Glacier National Park and the Bob Marshall Wilderness, and the Greater Yellowstone Ecosystem. Due to the mammals’ widespread territory and elusive nature, it’s hard for scientists to quantify population numbers, but best estimates put the number around 300 individuals.

Climate change remains one of the most prominent threats to the species as studies have repeatedly identified snowpack as one of the strongest indicators for wolverine distribution and density. Declining snowpack, and especially rapidly melting spring snow in alpine regions, will greatly limit the creature’s range throughout the mountainous regions of the country.

In addition, increased human development and infrastructure contribute to greater fragmentation of wolverine populations. This is another reversal from the 2018 assessment, which concluded that roadways were not an obstacle for wolverine travel. More recent studies have shown greater tendencies by female wolverines to avoid crossing roadways, and that even low-use forest service roads negatively correspond to wolverine distribution in the winter, especially in high-recreation areas. Restricted movement between core population areas limits genetic diversity, which is key in a species’ sustainability.

“The best available information suggests that habitat loss as a result of climate change and other stressors are likely to impact the viability of wolverines in the contiguous U.S. through the remainder of this century,” the report concludes.

Agency officials with FWS will use the latest addendum findings in their reassessment of whether wolverines qualify for ESA protections, which is expected later this year.

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