Secrets Under the Snow

by Denny Olson

It happens with regularity every year. In the early winter, before the winter rains can crust that early puffy snow, I stop to listen to the incredible silence, and then spot something that makes me remember. The snow under my snowshoes is alive.

This year it was an ongoing drama left behind in the surface snow – a polaroid snapshot of a classic predation story. An owl had left behind a body print with a wingspan as large as mine. “Great gray,” I guessed to myself. The hole punched by its talons went to the ground through knee-deep snow. At the bottom I could even pick out the clear impression of a talon – two toes in front and two in back – which confirmed “owl”. The outside “zygodactyl” front toe had swiveled around to the rear for more efficient prey-snatching. And, a tiny spot of blood there confirmed what every owl knows by sound alone. The snow masks secrets.

Vole – Photo Credit: Jake Bramante

In addition to the fact that it is opaque, snow is nearly perfect as a masking agent. The upper layers weave together like goose down, and that’s precisely why the lower layers are so interesting and alive. Even though it is frozen, snow is a great insulator. It can be thirty degrees below zero air temperature, and thirty above at ground level. Snow traps the earth’s body heat (“geothermal”), and melts the bottom layers into a lattice-work of caverns called the “depth hoare”. Among the Inuit and Inupiak people’s fifty-some words for different kinds of snow, this layer is called “pukak”. It is mostly empty space – and a playground for furry little “secrets”.

Most of those secrets are small and nocturnal enough to be nearly as secret in the warmer months. The smallest is the pygmy shrew, an insectivore two inches long in body-only length, and weighing as much as a penny. It may be the smallest mammal in the world. Masked shrews are only slightly larger, and, contrary to the usually descriptive and practical nomenclature of small mammals, has no mask. Biologists have increasingly called it the cinereus shrew after its species name.

Vagrant shrews, despite their name, do no more wandering than most other shrews. Perhaps they earned their name by having large food caches in scattered spots. They are almost twice the size of the two smallest shrews. Montane shrews are similar to the vagrant, slightly larger, and prefer higher elevation habitats.

Water shrews will more likely be under the ice along moving water – even in the high alpine. They dive for their insects, insulated by thousands of tiny air bubbles in their fur, and propelling themselves with large hairy feet. They have to work to stay submerged because of all that floatation they carry.

Shrews have never adopted hibernation as a cold-weather strategy so they are universally ravenous. They need somewhere between 1.5 and 3 times their body weight in food every day! (That would translate to one large elk per day for me.) They burn their candles at both ends – 103 body temperature, 600 heartbeats per minute, 300 breaths per minute and an average lifespan of six months! They are the original type-A personalities.

Most of our shrews also have an unusual habitat requirement. They need a minimum of 65 percent humidity in their air, or their overactive lungs will dry up and hemorrhage.

So, the pukak layer suits a shrew’s needs perfectly, moist air, easy travel, and other animals to eat. It is not out of the question for a voracious shrew to eat animals even larger than themselves.

In general, of the denizens of the pukak layer, shrews have pointy, sensitive noses, tiny eyes, and no visible ears. Voles have large ears and short tails, and mice have large ears and long tails. Meadow voles live in meadows, bog voles (lemmings) live in bogs and wet sedge fens, red-backed voles have a reddish back and live in old growth forests, and water voles live near running water in the alpine. Woodland deer mice look the color of a whitetail deer and live in the woods. White-footed mice have bright white feet and live up to the lower elevations of the east side Rocky Mountain Front. The only mouse hibernator we have is the Western Jumping mouse (which looks like a mini kangaroo and can leap up to 20 times its body length – go figure).

All of the others above have to scrape out a living beneath the snow, in the depth hoare. Many, probably most, don’t make it. Owls eat them. Hawks eat them. Weasels eat them. Martens and mink eat them. Shrews eat them – and each other. Cold freezes them. Starvation shrivels them. It’s not an easy life as a small mammal, and it’s usually a short one.

There really is only one way to cope effectively. Whoever said “be fruitful and multiply” must have been observing small mammals. Some have as many as ten litters every year. The strategy is a familiar one to us. Every hour or so, another McMeadow vole franchise opens up, and hangs a sign “Over 500 trillion produced …”

So if you want to be privy to the secrets beneath the snow, watch for those little tracks crossing compacted ski and snowshoe trails (where they have to climb over their collapsed cavern system) and dig down to the pukak for trails and an occasional dropping or two – a subway system on a scale you never imagined. And as you walk calmly on the upper layers of snow, remember the chaos below your feet. With a layer of snow, “more than meets the eye” is much more.