As the snow falls, settles, melts and is refreshed by new layers, each new surface shows signs of animal life.
Animals of the north need snow. For many small mammals, the more snow the better.
In our habitat, the mice, shrews and voles all have an important role as prey to the larger mammals and other predators up the food chain. These small mammals are important because of their abundance and for some because of their year-round activity.
Early in the winter, when the snow isn’t deep, the small mammals are vulnerable. High metabolism requires them to eat frequently so they remain active even in cold weather. They forage in the leaf litter on the forest floor and in networks of tunnels in grassy fields, and are prey to predators who use either vision or scent to hunt them. In winter they are no longer protected by overhanging tree canopy or brushy vegetation.
Pennsylvania State University’s website explains what happens as the winter progresses: “Falling snow gathers on the surfaces of the irregular profile of the leaf litter and forms complex arches and domes over and above the dead plant materials. Heat from the unfrozen soil and also from the decomposition of the organic molecules in the leaf litter melts the contact snow layer which quickly re-freezes to form thin ice sheets which add to the structural strength and also to insulating potential of the forming snow pack.”
This layer is referred to as the subnivian layer and is a unique winter micro-habitat. Some people call the layer of snow and space at the surface of the ground “pukak,” an Inuit word. Pukak only forms on ground surfaces, not on ice surfaces that are smooth.
Cold air keeps the snow cold but warmth from the earth keeps the very base of the snow pack from staying frozen. The snow protects the tunnels of the mammals and allows them to travel quite far under the snow. The snow pack also gives the complex microbial and insect life at the soil surface enough insulation to maintain metabolism.