Wolverine screenshot.

A wolverine recently ran past a trail camera in Yellowstone National Park.

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When biologists set up cameras to monitor wildlife in Yellowstone National Park, they never know what animals might cruise by.

That’s why it was a fun surprise for wildlife biologist Daniel Stahler to catch a glimpse of one of the park’s rarest creatures via a remote trail camera this December. The video taken near Mammoth Hot Springs shows a stocky wolverine barrel across the frame before it disappears into the trees.

The footage was the first to ever capture a wolverine in Yellowstone, though biologists know the animals regularly pass through the park. Stahler said he spots wolverine tracks most winters while he conducts field work, but monitoring the species is challenging.

Wolverines are solitary, medium-sized carnivores in the weasel family. They dig dens in deep snow at high elevations. Detecting and studying the species in its rugged mountain habitat is difficult. It also doesn’t help that so few of the animals exist in and around the park.

Only two females and five males were documented in eastern Yellowstone and in adjoining national forests during a study conducted between 2006 and 2009, according to the park.

The animals have wide-ranging movement patterns. Their home ranges spanned between around 64,500 acres to more than 313,000 acres per wolverine, according to the 2006-2009 study.

“It’s very easy for a wolverine to be detected in the northern part of the park and be the same as another detected down in the Tetons,” Stahler said. “They are quite incredible animals in that regard.”

Though no active monitoring of the species is being done, biologists often track wolverines using remote camera stations. They place beaver carcasses in trees and hope the scavengers climb up to take the bait. If a wolverine does, it rubs across a special hair trap. Biologists will collect the hair follicles off the trap for DNA samples and check the camera for footage.

Park biologists plan to set up some hair collection stations in the park next winter to help Wyoming conduct a wolverine monitoring project. But the wolverine footage captured in December came from an entirely different survey.

Stahler and other biologists had placed around 100 cameras across northern Yellowstone to track cougars. A wolverine happened to run by one of the cameras.

“It reinforces that our efforts to use remote cameras to study one species provide an opportunity to study multiple species,” Stahler said. “We hope to use data we get from cameras as a way to monitor a whole host of wildlife — not just the target animals like cougars.”

Lately, passive monitoring of wolverine populations has involved spotting tracks in the snow and gathering reputable reports when sightings occur.

“A lot of time people will get excited by a marmot,” Stahler said. “They’ll see a brown little furry thing hanging on the rocks in high elevations somewhere and think it’s a wolverine.”

Stahler said it’s difficult to know exactly how many wolverines are in Yellowstone, and he doubts any of the animals exclusively use the park. Maps from the 2011 report showed the highest concentration of wolverines moved through the mountain ranges at the northeastern and southeastern boundaries of the park.

It surprised Stahler to see that a wolverine was captured on camera at a lower elevation — around 6,000 feet. He guessed the wolverine had probably been crossing through to get from one mountainous area to another.

“It wasn’t like this was a camera we had at the top of a high, rugged mountain,” he said. “It was just outside of Mammoth Hot Springs.”

To Stahler, the sighting illustrated why it’s important to have large swaths of undeveloped, wild places where animals can safely travel.

“Highway systems, heavy logging operations and human-altered landscapes could provide barriers to movement,” he said.

Other factors that could threaten the species’ persistence include trapping and climate change. In Montana, wolverines are still considered furbearers, though the species’ trapping season was closed indefinitely in 2012. The Fish and Wildlife Service in a 2018 species status assessment estimated their population was at a little more than 300 animals throughout the lower 48 states.

For years, the Fish and Wildlife Service appeared poised to list wolverines as a threatened or endangered species. The agency proposed listing the animals in 2013, but decided not to a few years later. In October the agency determined its “best available science” indicated the species was healthy in the contiguous United States.

“In the time since our original proposal, the science on wolverine has been greatly advanced thanks to the work of state wildlife agencies and researchers in the U.S. and around the world,” wrote Noreen Walsh, Regional Director for the service.

This December, a coalition of conservation groups sued the agency over its decision. They claimed the Fish and Wildlife Service failed to adequately consider the ways in which climate change, trapping and habitat loss might contribute to a decline in populations.

”The Trump administration decided that they weren’t going to list wolverines under the Endangered Species Act and then made up the science to support that decision. This is yet one more example of how corrupt this administration is,” wrote Mike Garrity, executive director of the Alliance for the Wild Rockies, one of the groups that sued.

The lawsuit is still pending in U.S. district court.

Stahler said even if the species isn’t listed, many states are eager to manage wolverines without using hunting or trapping seasons. He is more concerned about climate change threatening wolverine habitat.

”Yellowstone will hopefully always provide good habitat for wolverines to find as use as part of their home ranges, whether they’re exclusively in the park or trans-boundary,” Stahler said.

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Helena Dore can be reached at hdore@dailychronicle.com or at 582-2628.

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