Busy Place that Subnivean Space!

Image of a drawing of small animals under snow

Many folks in the Renfrew County area are talking about snow these days. “Will it ever Stop?” “Not more snow!” “Can’t wait for Spring!” And on we grumble. But believe it, or not, that dreaded (for some) winter white stuff is creating a whole habitat underneath it. The space that develops between the snow pack and the ground on our lawns and in our woodlots is called the subnivean space. Subnivean by definition means ‘under the snow’. If you are a small mammal, it means a travel corridor that is a whole lot warmer and safer than running around on top of the snow.

This virtual highway forms as the snow accumulates on the surface of the ground. It especially forms when the ground surface is not frozen solid and when the snow starts to accumulate. As the snowpack piles up, the warmer surface of the ground melts away the lower layers of snow, and then quickly freezes a roof layer of ice forming a gap between the ground and the snowpack. The insulating snow above keeps the temperature of this space just below the freezing mark, which can be much warmer than when the temperatures at the surface are in the -30⁰C range. For voles, mice, shrews and even Red Squirrels, this subnivean space provides a source of food in the form of seeds and insects that they can access without being exposed to predator dangers or lower temperatures found at the snow’s upper surface.

Red Foxes, Coyotes, Owls and over-wintering hawks can be seen sitting very still as they hunt on the snow’s upper surface. They listen for the scampering of little rodent feet through the grasses and leaves that form the floor of the subnivean space, and then pounce in hopes of ploughing through the snow to capture their prey. Winters like this though, put the advantage on the side of the little guys, however, as the depth that the predator must dive through is so great that the prey they were hoping to catch has managed to escape by the time they get through ‘all that snow!”

That ‘blanket’ of snow, as we often refer to it, isn’t just covering the ground, it is insulating and hiding a whole host of activity that is sometimes evident in the spring, when the snow has just about melted and we see the worm-like trampled grass maze-like patterns left by those little feet that travelled through that busy space called the subnivean space!