Footprints in the snow

Footprints in the snow vanish into the enigmatic Subnivean Zone, a hidden world beneath our feet.

When I was a youngster, my twin brother and our neighborhood friends often visited a local bird sanctuary to seek animal tracks after a snowfall, though our primary outings involved clearing the pond to play hockey. Many decades later, after a snowfall, I would hike in the East Swamp Wildlife Management Preserve, the Wolfpit Preserve, Huntington Park, and the Franc Preserve with my miniature schnauzer Jake in search of animal tracks. As children, we did not understand the importance of seeing a variety of animal tracks, simply knowing that squirrels travel from one tree to another and mice leave tiny tracks. We never wondered how small animals such as mice, voles, and shrews survived the winter. Didn’t most other animals, such as bears, chipmunks, and groundhogs, hibernate while birds migrated south? We also never thought about insects when the pesky mosquitoes and flies were gone.

I’ve come to understand that every animal residing in Bethel has its strategy for dealing with winter. Migration and hibernation are common strategies that most of us are familiar with. However, a third strategy, snow insulation, depends on the snow. Snow as a winter survival strategy? Yep! While our residential homes are constructed out of wood (some with stone and wood), the Indigenous people of Canada's Central Arctic and the Qaanaaq area of Greenland constructed their homes (Igloos) out of snow blocks.

For some animals that have not migrated, hibernated, or sought the warmth of our homes, Mother Nature has provided an additional winter survival technique - a layer of snow that enables them to survive the winter weather. Underneath this layer of snow is called the subnivean zone. "Sub" means beneath, and "NIV" translates from Latin to snow.

The subnivean zone is the space between the surface of the ground and the bottom of the layer of snowpack, which provides protection from the winter's bitter cold and winds while also providing some shelter from predators. A subnivean zone can be created by several different processes, one of which is when a snowfall lingers near a rock, shrub, or tall meadow grasses, blocking snow from accumulating underneath and resulting in an air pocket. Accumulated snow partially melts and then refreezes, creating a hard layer.

Mice, moles, and shrews are the main inhabitants of the subnivean zone. They create a network of long tunnels, complete with air shafts, to the surface above. This network not only provides them with access to food but also serves as a vital part of the ecosystem. Grass, seeds, leaves, bark, and insects are all part of the food chain, and the elaborate tunnel systems these creatures create are a testament to the interconnectedness of nature.

It takes only six inches of snow to enable mice, voles, and shrews to have a sturdy roof over their heads and roomy living quarters below. The subnivean zone remains within a degree or two of 32°F, regardless of the temperature and weather conditions in the outside world, protecting the mice, voles, and shrews from freezing to death. Most tunnels begin where there is a tree trunk, large rock, or thick bush. These dark surfaces also absorb solar heat, helping moderate the temperature of the animals, plants, and ground.

Living under the snow is not without risk. Owls can hear mice and voles running around underground while foxes and coyotes detect by scent.

Suffocation is a hazard for those left behind in a collapsed tunnel. Come spring, the subnivean dwellers face other challenges. A sudden thaw or early rain can drown them as water floods their home. In addition, alternating thaw and freeze of the snowpack, weakens its structure. Eventually, the snowpack will collapse forcing the residents to vacate the tunnel system.

As spring progresses and the last of the snow melts, the ingenuity of these seldom seen subnivean specialists is spelled out like a map: telltale humps appear where tunnels had crisscrossed the field from tree to rock and beyond. All evidence of this survival strategy will disappear when the grass greens up.

So each winter as the snow accumulates, remember not all creatures have bedded down for the winter, sleeping away winter’s cold weather. After a snowfall, enjoy nature and take a hike in the snow with your significant other, your children, friends, and/or dogs, and look for the little creatures that make tracks back and forth across the snow only to disappear into a small hole in the snow.

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