This might sound like the title to a horror show, but during the winter, an amazing amount of activity is occurring right underneath the snow. Another world of tunnels, bedrooms, kitchens, and even latrines fill the space between the surface of the ground and the bottom of the snowpack. This cozy area is called the subnivean zone, and it’s the place where many small mammals survive the long winter months.
For small mammals facing the cold temperatures and bitter winds of winter, an insulating layer of snow is the perfect solution to staying warm. With six inches of snow or more, the subnivean zone actually maintains a temperature of 32°F, even when conditions are much chillier above! Living in the subnivean zone also protects these snack-sized critters from hungry predators and allows them to still access grass, leaves, bark, seeds, and insects--a variety of nutrients needed to last through the winter.
But how do these tiny mice, shrews, and voles not get crushed by the weight of the snow? Vegetation like tree trunks, branches, and other plants can physically hold the snow up but, there is also another phenomena at play. A sort of “ice roof” forms when heat from the earth melts snow into water vapor. The gas moves up through the snow pack, changing the lowest level of snow into ice particles that act as an insulating roof. Spaces carved out by tree roots, stems of plants, and other vegetation, along with air shafts dug to the surface by the local residents, allow for enough oxygen to reach this layer underneath the snow.
The next time you take a walk through the snow, just remember about the many creatures lying just below the surface. But don’t worry, most of them are cute and fuzzy, not the monsters in a horror show!
[image description: Snow and coniferous trees line the banks of an icy, small creek that flows into a larger river.]
