The Subnivean World

Listen Now

As we look out on the snow covered landscape during winter, it often looks quite placid, almost abandoned. But looks can be deceiving, and although we certainly see birds and other animals above the snow, there is an active world under the snow.

I was reminded of this Subnivean, or “under snow” world after a recent snowfall when I saw the distinct arching tunnel of a small mammal (probably a shrew) cross the road near our house. It made a direct line across the asphalt to the trees on the other side. It appeared that this little critter knew where it was going.

The subnivean world is typically a one-two inch space between the ground surface and overlying snow. Temperatures here remain near the freezing point for much of the winter even though air temperatures may drop to well below zero.

The problem for these subnivean occupants isn’t so much the snow, but the cold. To win at this game, animals must conserve heat. But that doesn’t necessarily mean they can’t be active. Many of these animals are amazingly active during the winter. They’re not just surviving. They’re growing, prospering, and in some cases even reproducing.

Common occupants in this subnivean world include small mammals such as shrews, voles, and deer mice. Some mice and voles are solitary much of the year, but congregate during winter in communal nests to conserve heat. Although congregating may increase their vulnerability to predators and the incidence and spread of parasites and disease, these risks apparently don’t outweigh the advantages of heat conservation.

Voles construct a lot of tunnels, some of which dead-end near the snow surface. Although the function of these dead-ends isn’t well understood, they may function in ventilation or perhaps as “sky lights.” Look for the remnants of these tunnels (and nests) next spring when snow melts. The trails are often quite conspicuous in road ditches. The sinuous, two-three inch wide piles of grass clippings with the occasional big pile are a dead give-away.

The next time you look at the snow draped landscape, give some thought to the life under the snow. Across much of North Dakota the subnivean world is a surprisingly active place.

Chuck Lura

Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.