You may have seen mysterious vein-like tendrils in the snow before, do you know what they are? Roots covered by snow? Perhaps a symbol left by aliens?
While some lumps are just snow-covered objects on the ground, these pathways are left by small mammals like mice and voles as they hunt for food in the winter! When conditions allow, they will move throughout the subnivean zone, the space between the ground and the snowpack above. As the snow must be thicker to allow for a roomy subnivean zone to form, we usually don’t see the world they create under the snow until it melts. As the ground holds heat, when it gets covered by a layer of snow, the snow closest to the earth begins to melt, evaporating and condensing to create a space with an icy ceiling and bare ground.
So how are these tiny mammals surviving in the Subnivean zone through very chilly winters? Let’s begin with the conditions they are living in. If you have ever been inside a snow fort or quinzee, you may have noticed that snow can serve as insulation from the cold and wind. The Subnivean zone is very similar, insulated by the layer of snow above it, and the ground below. So while it may be -30 degrees Fahrenheit above the snow, below the snow (once it reaches about 6″) it sits very near 32 degrees consistently. Don’t get me wrong… this is still chilly, but wouldn’t we all choose 32 degrees over anything negative?
How all living things survive the winter can generally be sorted into two categories of adaptation, behavioral and physical. Migration is a behavioral adaptation that allows those animals to avoid the cold altogether, and hibernation is a blend of physical and behavioral. The behavioral adaptations are preparations like eating more and finding a safe space to hibernate, and the physical adaptation is their body’s ability to slow down their heartbeat and metabolism to a rate that allows them to exist in that state for months. So, again, we ask “How do these tiny mammals do it?”
Behavioral AND physical adaptations! There is plenty of food still available beneath the snow in the winter for mice and voles, like seeds, leaves, roots, and bark. Behavioral adaptations include using the subnivean layer to search for food and being, in general, much less active than in warmer months. Physical adaptations allow mice and voles to slow their metabolism and heart rate for shorter periods than hibernation in the case of extreme cold or lack of food. This adaptation is called torpor, and many animals use it as a way to survive adverse conditions, including hummingbirds, skunks, and squirrels. If you’ve ever heard of non-native green iguanas falling from trees when it gets cold in Florida, torpor is why! It is just too chilly for them and their bodies are trying to cope.
With all of that cover, they must be safer too! Right? Well just as they have adapted, their predators have too. Red and grey foxes, as well as coyotes, are excellent predators in the snow with their skilled hearing and smell. In addition, Minnesota has seen an irruption of owls in 2025 and these predators have keen hearing that allows them to hear under thick snow! Their ears are asymmetrical, allowing them to pinpoint the direction sound is coming from with incredible accuracy.
Now when you see the evidence of life in the subnivean zone, share with a friend what you know! And if you want to learn more, there is a great article by Ellen Horowitz for Montana Outdoors that has some fabulous photos and in-depth information. For kids, we recommend the Wild Kratts episode called “Journey to the Subnivean Zone” (26th episode of season 2).