Den Search

A few weeks ago, Jerry Longobardi,  Wyoming Game and Fish game warden for Teton County, came across a hole in the snow on the west side of the Tetons, with wolverine tracks leading into and out of it. Photos of the site circulated among WY Game and Fish, WCS, and NRCC, and the verdict was clear: they were wolverine tracks. The critical question was, was the hole a den, or did it simply represent a food stash, or a curious wolverine digging in the snow for a rodent?

The hole, with wolverine tracks

WCS ran a research operation in the Tetons for many years and documented what to date remains the only confirmed instance of wolverine reproduction in Wyoming, also on the west side of the Tetons. WCS is still the primary research organization for the Tetons even though they are not currently operating traps here. But because their operation is based in Montana, coming down to Jackson to investigate the site would have been a haul. I volunteered to ski in with Jerry a few weeks after the original sighting, to see if the area was still being used and, if it was, to try to collect DNA samples by picking up some scat. We set out on Friday. It had been snowing heavily for the past six days, pure wolverine weather, and as we headed west, the prospect of finding a den buoyed my spirits more than the first glimpse of sunshine in a week.

The chances of stumbling across a wolverine den by accident are minute, and den detection remains one of the elusive objectives of most wolverine research projects. An instrumented female will provide a location by localizing – staying in one spot for a number of days – which wolverines seldom do unless they are denning. But detecting dens this way requires a trapping operation before the denning period, reliable capture and instrumentation of female wolverines in the region, and the money and skilled pilots to fly repeat telemetry flights in rugged mountainous terrain three times a day over the course of four days at the beginning of the denning period. If all of these circumstances come together and the instrumented female is picked up in the same location over the course of the four days, then you know you have a den. This method is time consuming and expensive, due to the front-end investment in trapping in remote locations, and the costs of telemetry flights. For years research operations have tried to develop flight-based surveys for dens, but despite the Absaroka-Beartooth Project’s success in developing a flight-based systematic survey for presence-absence of wolverines in a given region, no one has been able to reliably locate dens of uninstrumented females from the air. So finding a den by any means other than telemetry is rare.

The site, as pointed out on the map, was not in what I would have considered denning habitat – generally, one thinks of a mother wolverine choosing to situate herself in a high cirque, and the forested ridge where Jerry had come across the hole didn’t seem quite right. But then again, what do we really know about wolverine denning habits in the Tetons, with only one den ever discovered? Besides, I wanted it to be a den, so I suspended judgement and remained optimistic.

We took a snowmobile for the first few miles and then skied in from there, not wanting to disturb the wolverine, if she was there. GPS coordinates led to a swath of snow on a steep hillside,  where despite high hopes, there was no further sign of disturbance. We removed our skis and slid down the slope to investigate for tracks, but there was nothing. My heart sank almost as deeply as I did – the snow was thigh deep and I plunged through the bottom of the snowpack and snagged my foot in a tangle of branches. In the struggle to extricate myself, I ended up upside-down, head pointed downhill. It might have been a dangerous situation if I’d been alone, but it also illustrated that this could indeed be denning habitat. Wolverines seem to favor slopes underlain by either sizable talus, or downfall. It seems that they dig into the snow for access, and use the cavities formed by the boulders or trees to provide structure to their dens. The hollow that I’d fallen through, and the branch that had snagged my foot, would be perfect for a wolverine. And the depth of snow, along with the cover provided by the forest, suggested that the snowpack would probably be adequate to provide necessary cover through mid-May, when wolverine kits are finally independent enough to travel on their own.

We dug into the den site until we hit ground, but found nothing – no sign of bones or of anything else a wolverine might have been eating. Jerry had found a second hole several hundred yards uphill from the first, so we skied up to investigate that as well. Again, there was no sign, and because the snow was terrible, we called off further searching and headed back.

Later, Jason said that the lack of tracks didn’t necessarily mean that it hadn’t been a den. Female wolverines generally occupy a series of dens in the course of raising their kits – a natal den, in which the kits are born, and successive maternal dens, in which the kits are nursed, raised, and eventually weaned. Jason estimated that a mother wolverine moves about 300 yards between den sites – which was approximately the distance between the first hole that Jerry found, and the second.

Even if it wasn’t a den, Jason suggested that it would be a good idea to go back and dig more extensively to see if we could uncover some sign of what the wolverine might have been doing in the hole. Food habits data, while not quite as thrilling as the prospect of finding a den, are also rare and valuable.

We’ll give it a few weeks, and then I’ll head back up to check out the site again.

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