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Scientists Teamed Up With Microsoft to Make Wolverine-Luring Skunk Bombs

Wolverines may be critically threatened in the American Northwest.
Image: Woodland Park Zoo

If you want to study wolverines with Robert Long, senior conservation fellow at the Woodland Park Zoo in Seattle, you'd better be okay with smelling like a skunk. That musky scent (mixed with a little castor oil and a touch of anise) emanates from dispensers installed at Long's winter research sites throughout the North Cascades Mountains in Washington State.

Winter is the best season in which to study wolverines—work that is critically important, given their pending status as a threatened species. But, two years ago, a winter study was impossible for Long. Dangerously deep snow packs and steep avalanche slopes prevented biologists from returning regularly to the remote camera and hair snagging sites, in order to replace the wolverine-luring bait. (Back then, they were using things like rotting beaver carcass.) With a little help from Mike Sinclair, an engineer at Microsoft, Long came up with a smelly solution to make winter study possible.


"We're dealing with a critically threatened population. It's not known how they will deal with long term concerns like climate change"

Long and Sinclair, with biologist Joel Sauder from the Idaho Department of Fish and Game, developed a scent dispenser based on an ultra-low power control processor, which is powered by lithium batteries. This air 'de-freshener' has a tiny peristaltic pump designed to release three milliliters of skunky smell each day for six to nine months.

Researchers prep the lure. Image: Woodland Park Zoo

During the fall of 2015, Long and his team put scent dispensers out at 24 stations in places they expected wolverines to visit. Cameras, hair traps and dispensers were placed a minimum of four metres up trees to account for the massive snowpack that would accumulate over the next eight months. Then, they waited to see if the skunky scent dispensers would work.

New results say yes. According to as-yet-unpublished research, the team detected wolverines at 13 locations, identified by varying colour patches on their chest fur, visited the sites over an eight-month period in 2015/16. "That represents a huge increase in the number of detections over any of our previous survey efforts from the summer," said Long, who had only detected individuals at four locations when he conducted surveys over the three summers previous. (There was no way to do winter research at that time, so he stuck to the warmer months.)

In most cases, the first wolverine wasn't detected on camera until five or six months after the scent dispensers were deployed. "Wolverines are probably scarce on the landscape and moving great distances," said Long. "They are only in any one place infrequently, even in places we expect them to occur." However, he added, it's good news in term of the longevity of the dispensers, in that they were still luring wolverines that far out from deployment.


Image from a camera trap photo, taken by remote cameras that accompany the dispensers. Image: Woodland Park Zoo

While the smell drew them in, wolverines were not easily fooled. At most stations, Long said the wolverines only hung around for a minute or two. They would climb the tree toward the scent dispenser, investigate a bare bone that was hanging underneath, and quickly realize there was nothing to eat. Then they were out of there.

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"Over the eight-month period the stations are operable, the wolverine might visit once, and only for two minutes. So it's really key that our equipment is working well," he said.

Seventeen of the scent dispensers were still squirting out skunk smell upon retrieval in the spring of 2016. The other third worked for at least part of the winter. With Sinclair, the team was able to identify what contributed to any failures, and develop an upgraded version that will last over a longer period of time.

This fall, Long and his team deployed another round of dispensers at winter research sites to help collect wolverine data.

This comes at an important time for wolverines in the American Northwest, as understanding their populations numbers may be key to a correct listing under the Endangered Species Act. In 2014, the US Fish and Wildlife Service (USFWS) withdrew the proposal to list the wolverine as a threatened species after "concluding that the factors affecting it were not as significant as were once thought." However, a district court in Montana overturned the USFWS withdrawal, forcing them to reconsider the listing. As a result, the USFWS was soliciting any new information on wolverines through their commenting process in the fall.


Image from a camera trap photo, taken by remote cameras that accompany the dispensers. Image: Woodland Park Zoo

A threatened listing means this wolverine population is likely to become endangered within the foreseeable future, throughout all or a significant portion of its range. I asked Long if his findings support the listing.

In the most positive interpretation of his preliminary results, he said there may be only 20-40 individuals in the area. "We're dealing with a critically threatened population. It's not known how they will deal with long term concerns like climate change, or short term concerns like moving across transportation corridors, roads, and through other human disturbances to the landscape," he said.

Armed with new technology, Long aims to find out, one skunky smelling research station at a time.

Correction: An earlier version stated that 13 wolverines had been detected, when in fact wolverines were detected at 13 locations (not necessarily adding up to 13 animals). In addition, during the previous three summers, wolverines were detected at four locations—again, not necessarily four wolverines. The original piece also contained a caption error in the lead image. The piece has been updated to reflect these changes.

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