But it's not really all that mysterious. Many small animals would never survive the winter cold without the subnivean space. While the snow cover builds up, the ground is giving off heat. This creates water vapor, which condenses and freezes under the bottom layer of snow, creating open spaces at ground level. It's almost as if the snow peels away from the ground, leaving pockets where mice, voles, and shrews spend the winter.
Some predators live there too, including weasels.
You can see signs of the life under the snow by looking at the edges of ski or snowmobile trails. The trails break through the subnivean space, often cutting across tunnels created by animals living in the snow. Wednesday During the winter, big mammals like the black bear are able to retain heat better than small animals. That's because, pound for pound, bears expose less skin to the cold. The bear burns the fat it builds up over the summer and fall.