Beneath Deep Snows: Mysteries of the Pukak

Deep snows on this north facing hillside require the use of snow shoes while looking for animal tracks far into this mixed hardwood and conifer forest. I’ve used snow shoes since I was a child and so they seem to be a natural extension of my body when their use is required. My snow shoes are large, about three feet long and a foot wide, to support my 275 pound frame on these snow depths that exceed three feet. The snow is still light and fluffy, nearly unchanged since it accumulated in these woods, due to the very cold temperatures that have covered the entire region this winter. On this day, late in February, it is a balmy 12 degrees nearly 20 degrees warmer than yesterday morning.

I expect the tracking exercise in this significant snow coverage to be relatively unfruitful. Life in the northern woods compels that all wildlife be masters of survival. Surviving a cold winter with deep snow comes down to two primary elements: energy conservation and food. The food part is not a problem this year for most wildlife. There was a good crop of acorns this past autumn, a decent beechnut crop as well, and these woods hold large areas of accessible branches and buds due to past logging practices. The energy conservation issue is a gigantic problem. Traveling through deep snows in search of forage is more than difficult for both herbivores and those that predate them. The fact is that for most wildlife, predators and non predators, the act of seeking out food in these conditions will use more calories than the food can provide. This is quite simply a prescription for starvation.

The result is that much of the wildlife in this area such as white tailed deer, wild turkeys, fox, and eastern coyotes for example have, for the most part, migrated to lower terrain. Areas along major rivers may now hold concentrations of wildlife. Although there is competition for food in those locations there is adequate sustenance to survive. The snow pack along rivers in the valleys is often not nearly as deep as in the higher terrain. Energy conservation is not as big as an issue. There is a better chance for survival.

Other species such as squirrels, porcupine, fisher, and weasels are not as impacted by deep snows. However the amount of time they spend in trees during the late winter may limit tracking to a tree to tree scenario.

On this day in more than two hours of trekking in deep snows through a large area of the winter forest has yielded two sets of moose tracks, evidently a very large cow and her calf, and a set of bobcat tracks on top of a long stone wall The winter forest feels empty and stark. There are long, dark shadows of trees swaying back and forth in a stiff breeze looking like they are sweeping the surface of the snow. This seems to be the only active sign of life. I am in no way discouraged. I am cognizant of the mysteries of the winter woods and I know that the forest is multi-layered when it comes to wildlife and their habitats. There is likely much activity deep underneath my snow shoes amongst the leafy layer of the forest floor buried at the bottom of this significant snow pack.

I love that I have to use my imagination when thinking about life beneath the snow. In my mind I can see red back and woodland voles, short tail and pygmy shrews, white footed and deer mice, and a host of other creatures living in tunnels in this dark frozen environment. These animals ranging from insects to small mammals live in a seasonal and reasonable temperature of 32 degrees. Here some critters feed on seeds, vegetative remains, and the cambium on small woody stem vegetation. Some critters feed on other critters. And some critters feed on both.

The real beauty of this “beneath the snow” environment, technically referred to as a subnivean habitat, is that it is the result of a complex network of pure physics, biologic activity, and sheer happenstance. It is nearly the perfect environment for animals that are very small, in fact so perfect, that it allows them to not only survive but flourish during the harshest time of year.

The Innuit, being intimately familiar with their cold world habitats, gave this particular subnivean habitat a name: pukak. The pukak tunnels are, in fact, not the result of small rodents tunneling through the snow as commonly believed but rather the result of physical processes that small animals and rodents utilize as part of their winter world. The formation of the tunnels within the pukak requires several key elements; vegetation beneath the snow, a semi-gradual change in outdoor temperature, and snows of at least 6 inches, but preferably 12 inches or more.

The pukak tunnel begins forming in the late fall at the arrival of the first snows of the season where vegetation is present. The vegetation holds some of the snow off of the surface of the ground. Miniature snow caves are formed. Ice crystals develop underneath the thin layer of the early winter or late autumn snows. As winter progresses and the snow deepens a temperature gradient develops caused by the warmer ground temperatures below and the colder air temperatures above. This causes water vapor to rise and freeze which creates small tunnels at the base of the snow pack usually no more than 2 inches high. It is these small tunnels, some of them going for very long distances, that produce the subnivean habitat so readily used by small rodents, insects, and other tiny animals that, in fact, all contribute to this new winter habitat. These habitats stay right around the freezing mark. This is much more hospitable than temperatures above the snow that can fall well below the zero degree mark for much of the winter. The warmer temperatures found within the pukak translate into better energy conservation. The more energy preserved the better chance for survival.

Like any other ecosystem the pukak is a well developed, codependent, habitat. Voles and mice consume seeds, roots, and other vegetation matter. Shrews may consume insects, millipedes, baby voles and mice, and any other source of protein they can sink their teeth into. The fact is that some shrew species have to eat several times their own body weight everyday. While consuming vegetation voles and mice may move seeds to new locations, introduce fungi on translocated forage to new locations, and aid with the important process of decaying vegetable matter to make it more available as a food source for larger plants and animals.

While the pukak does offer a certain amount of safety for its inhabitants given they are visually hidden from above the snow pack predators it does not give them absolute safe harbor. Ermines, or the short tail weasel, are particularly adept at harvesting live food from this frost lined channels underneath the deep snow. Ermines also have a voracious appetite, especially in the cold winter, and may tunnel into the pukak layer for an absolute smorgasbord along the pukak food court. Fox, utilizing precise telemetric hearing, can locate the exact position of a rodent under the snow and pounce on it and precisely locate the prey in a single attempt. Still, despite the risk of predators, the pukak does provide a wonderful habitat for many small creatures that otherwise would have a very difficult time surviving the harsh winters of the north.

I find great solace in knowing that there is a world, full of life, deep beneath the bottom of the snow shoes on which I stand. For now I will use my imagination to envision its activities. In the spring, when the snow is not quite melted I will be able to see the trails that remain at the bottom of the snow.

With these thoughts I start the cold, yet beautiful, walk home. A golden sun is sinking in the western sky. The once blue sky now yields to pink, orange, and yellow colors. Even lower temperatures seem to be settling in with the approaching clear night. I will look forward to my own winter habitat; a chair next to a warm fire in the wood stove. I envision a cup of hot cocoa in my hand while thinking about critters happily scurrying about within tunnels in the Pukak under deep snows. I picture a smile on my face and a warm, warm feeling in my heart.

How can I not love the winter?

Originally written for the Heath Herald in March of 2015

  • Montucky

    Once the snow melts here I love to see all of the signs of those who have lived all winter under the snow pack. There are many tales to be read there.

  • Wild_Bill

    Nearly countless numbers. Such a hidden and interesting world.

  • Ratty

    This reminds me to look more closely for signs of life, especially in the winter. For some reason I’ve been forgetting that in the last couple of years. There’s so much wildlife just around my house that I can go out my back door and see something. Just this last winter I began to remember to watch for animal tracks again. I realized how much I’ve been missing doing those things.

  • Wild_Bill

    One cannot look to closely at nature. Even when you think you’ve noticed everything there is more to find.

  • Teresa Evangeline

    We had very little snow this year, so this world underneath was not as possible, but in the meadow, Buddy always pushes his nose deep into tufts of grass, sometimes repeatedly, detecting the scent of a field mice or other small critter. It’s fascinating to think of this other world just under our feet … a lovely thought.

  • Wild_Bill

    And it’s mystical formation! My goodness I love how all things connect on this planet!

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