How the Wolverine Got Those Feet

Above: “Wolverine Number Two” captured by a remote camera at a cache site, with his travel-cover in the background. This is one of the study wolverines Squirrel-Eating Jon tracked over numerous consecutive winter seasons, identifying him by throat and chest markings as unique to each wolverine as a fingerprint. Jon pioneered the use of remote cameras for the purpose of identifying and keeping tabs on individual wolverines, a technique he introduced to other wolverine researchers from around the globe who then adopted the technology for themselves. The picture here is a bit blurry, the technology then was not what it is now.

The wolverine has the lowest per-square-centimeter foot-loading of any animal out there. That is, when they put the weight down on a foot, that weight is diffused over an area large enough that the pressure exerted on the ground is the lowest possible for the size of the animal concerned, and lowest of any creature. This is achieved because the wolverine, an animal about the size and weight of a cocker spaniel, has feet the size of a good-sized wolf – an animal four or five times its size.

A person would expect that spending life traveling about on such permanent snowshoes could be awkward at times. The wolverine didn’t evolve such paddles casually. Nature might produce such prototypes at random, but for them to become the standard, the experiment has to be a success.

So in the case of the wolverine, why was the experiement even attempted? Why did nature equip this animal so?

Squirrel-Eating Jon got some first-hand insights into the answer to this question during ten consecutive winters tracking this legendary beast in one of the world’s last great wilderness areas – the border country of northwest Alberta and northeast British Columbia. Passing back and forth across that imaginary boundary daily and not infrequently traveling up and down it. One province to one side, one to the other. Nothing to distunguish them on-the-ground.

A photo Jon took of the front track of a wolverine designating where the animal had travelled on a wilderness road recently cleared of most snow.
That is one big foot for an animal the size of a spaniel.

One of the first things Jon noticed with regards to wolverine in this landscape under the conditions of midwinter snow is they showed up in the uplands mostly, in precisely the sort of continuous conifer cover in fact where their small relative the marten was most abundant. If the crust was really heavy at some point in the winter, you might find their tracks in the lowland muskeg-and-bush mosaic where the wolves killed many moose which the wolverines could potentially take advantage of the leavings of, or in the desolate spruce fens where caribou secluded themselves. But overwhelmingly, they were an upland animal. The next thing Eating noticed in tracking them (or backtracking them for not wanting to stress them if the trail was particularly fresh) is that not only were they travelling under the spruce canopy, they had a penchant for picking the absolute densest stands to do so in. They would eat and cache food in more open stands where they could watch for approaching danger, but for travel nothing was more appealing to them than almost impenetrable stands of doghair spruce or, in a more impacted landscape such as a forest cutblock, a certain stage of pine regrowth that formed a solid-looking wall of young trees. The sort of growth where a human tracker often as not had to pass through sideways-on to get between the boles. The animals would skirt more open stretches if they had denser options – he picked up on this too. If they came to a broad open, you could see where they had climbed a tree to about man’s head-height, before coming down and taking a detour. You could absolutely imagine them up there scanning for cover, for the best route. And sure enough, when they came back down the tree they chose the option of densest cover. When they came to an open industrial cutline that ran east-west, they would travel just inside the edge of the dense growth on the sunny side, where the sun had further thinned the snow out, sometimes to just a few centimeters depth where the depth on the middle of the line might be to a person’s knee or more. If it was a north-south oriented line catching no signficant sun at either edge they would cross directly. Unless there were a compacted snowmobile trail on it, in which case they would take advantage of this wilderness sidewalk in 100% of instances observed, sometimes for several kilometers before regaining the bush. And in 100% of the instances observed, when they took once more to the woods, they did so where the cover was the absolute thickest.

The picture that emerged was of an animal on a very strict energy budget doing everything it could not to tip the balance into the red. And this is why the wolverine evolved such huge feet – as an aid in meeting that budget. Jon then considered yes, but then they are also found all winter on the wide-open tundra, how can this correlate? Well, the tundra is a semi-desert of low precipitation. The snow that is there is wind-packed. You don’t have the conditions of deep, low-flotations powder you have in the boreal forest, out there. Then he considered the other carnivores that shared the wolverine’s home in his study area. Particularly the coyote and the lynx, animals of similar size, and both prone to going pretty much anywhere, open or not. The lynx even having its own snowshoe feet. How did this compute? Well, the coyote and the lynx are not wolverine is how. Their energetic needs were more easily met in that landscape. The coyote could subsist on voles even, something the wolverine could not. The wolverine couldn’t even subsist on the hares that supported the lynx, even though the lynx too was on a constrained budget as evidenced by its own outsized feet. But the lynx could subsist on hares, and many years the hares were abundant. When they were not, many lynx starved, and this is likely why their feet were also so large. To help arm them for those years. But in years of abundance, the lynx needn’t limit their travels to a particular woodland cover type cos they could be pretty sure of an imminent meal that would sustain them. The wolverine meanwhile travelled vast distances, something the lynx and coyote did not do. Catching the odd hare after a chase here and there, yes, and maybe even bringing down the odd caribou or even moose as some did. They liked to catch and eat beaver as well (the Ojibwe name for them is “beaver eater”) but beaver of course were inacessible in winter. Mostly they relied on carrion to keep them going, the kills of wolves primarily. A random resource of low incidence spread over the vast distances the animal necessarily travelled. This was why the the wolverine needed to restrict travel under winter conditions of deep powder snow to the densest winter stands where the snow depth was heavily buffered and greatly reduced underfoot by the boughs and much easier to travel through. This is why in the landscape Jon studied them in they mostly limited themselves to the uplands where the option of densest contiguous cover existed.

And this is how the wolverine got such outlandishly large feet.