We have gotten so much snow this winter that it’s hard to imagine any animals are up and moving about. But underneath all that snow, many animals have stayed cozy and warm despite the cold temperatures.
How? The fluffy snow acts as a blanket, keeping the ground warmer than the air. This creates a space called the subnivean zone, which is what we’re exploring today.
The subnivean zone is the snow-free area that forms above the soil but below the snow in the winter. It can form in one of two ways. Sometimes it forms when branches or bushes hold the snow up above the soil. The other way it forms is when the snow is heated by the soil below. This turns the lowest layer of snow of snow into water vapor, which travels up through the snowpack, often forming beautiful ice crystals on the surface of the snow and around entrances to the subnivean zone on cold days.
Either of these methods creates a space large enough for small animals to scurry around. As long as there is at least 10 inches of snow, this space stays around 32 degrees Fahrenheit no matter the air temperature above.
Mice and voles are the most common inhabitants of the subnivean zone, but many animals use this space.
Mice and voles don’t hibernate all winter, though they do spend some time huddled up and sleeping. Instead they spend much of their time eating bark, seeds, plants and stored food from the summer. They also benefit from fewer predators, who have a harder time finding prey under all that snow. However, owls, foxes and coyotes sometimes catch prey by listening for movement under the snow, then pouncing.
Some predators, like weasels, are small enough to enter the subnivean zone to find their supper.
Explore the subnivean zone
Look for evidence of the subnivean zone. Head to a natural area and keep an eye out for animal tracks. You might see the tiny tracks of squirrels, mice and voles. Follow them as they bounce across the surface of the ice. Eventually, you will find that they disappear into a hole, usually around a fallen tree or a shrub. These holes are the entrances to the subnivean zone.
You can even see evidence of this under-snow world when the snow is gone. During the thaw, keep an eye out for tunnels on the surface of the soil. These are vole runways. Sometimes, you’ll find a ball of grass used to line a place to rest and stay warm. Raking these tunnels will usually restore grass after the winter. Don’t worry — the voles will build new ones next year.
Use a thermometer to measure the difference under the snow and over the snow. On a cold day or night, take a thermometer and find an entrance to the subnivean zone. You can also build your own little ice cave. Measure the temperature underneath the snow. Then compare the temperature above the snow. How does this work? The same way your sweater or puffy jacket does — it traps heat. Your sweater traps your body heat close to your body, and the snow traps the heat from the soil next to the earth’s surface.
Interested in learning more? I recommend the children’s book “Over and Under the Snow” by Kate Messner, and the Wild Krattz episode “Journey to the Subnivean Zone.”
Now get outside and explore the kingdom under the snow!
Hillary Clark is the membership and education coordinator for the Chelan-Douglas Land Trust. For more ways to get outside with your children, visit www.cdlandtrust.org/whats-new/events.