Refuge Manager’s Update February 2025

Life below the snow

By all accounts it’s been a snowy winter in Vermont this year. Looking out the window of my office there is a white blanket stretching as far as I can see. For many species of wildlife, winter is a time of inactivity, migration, and hibernation. But there is more out there than meets the eye. It occurs beneath the snow, in the subnivean zone.

I love the word subnivean for some reason. Taken from latin roots (sub and nives) it means “under the snow” and refers to an open shallow layer under a deep snowpack. Taking a walk through the snow you may often see small holes here and there with mouse tracks leading to and from them. What you don’t see are the tunnels which small mammals, like mice or voles, create under the snow. These tunnels link different parts of their habitat (areas for foraging, sleeping etc.) under the protection of the snow above them. While the outside air temperature may be well below freezing, the relative protection of the snow layer creates a rather stable climate in the subnivean zone, typically hovering around 32 degrees Fahrenheit.

One would think that a deep snowpack would be fabulous protection for the mice and voles who go about their business in tunnels in the subnivean zone, rather than being exposed as they are during the rest of the year. Although this does provide much cover and protection, predators are still active during the winter and still need to eat. Hawks and owls have developed excellent hearing and can detect rodents moving about in their tunnels under the snow. Also, other animals like the red fox famously leap high in the air to pounce on the unsuspecting vole scurrying through tunnels under the snow. However, the one animal that probably has the best predatory advantage is the weasel, specifically long and short tailed weasels. These predators have cylindrical bodies and can move easily through established rodent tunnels under the snow. Their coats turn white to camouflage them in the winter and they are known as voracious predators. Weasels will even take over a tunnel system to make it their own!

As you walk, snowshoe, or ski the refuge trails, keep the subnivean zone in mind. Look for the holes and tracks that provide clues to the activity under the snow. As snow melts, these pathways also become visible in the vegetation below the snow. And as I’ve said many a time, lets all be glad that weasels are not the size of dogs!

by Ken Sturm, Refuge Manager, Missisquoi NWR