by Lynne Flaccus
While we are out and about in the winter, trying to stay warm and keeping our feet under us as we navigate the ice and snow, how many of us really contemplate life beneath the snow? While many creatures and plants become dormant for the winter, plenty of activity continues under the blanket of snow as it builds up.
The “subnivean layer” is the insulated space between the snow cover and the frozen ground beneath. Many animals take advantage of this thin layer of warmer air and space to continue with daily activities. Though the temperatures under the snow may be near freezing, this layer provides a place for both plants and animals to survive the harshest winter winds and below-freezing temperatures at the surface. As snow settles and ice crystals reform, air spaces and loose snow provide another world for animals to move around in without being exposed to the extremes.
Many of the creatures taking advantage of this “insulating blanket” are the small mammals actively searching for food to keep their metabolic furnaces fired. For these creatures, as with any winter-active animal, they must balance the cost of being active and losing heat energy, with the amount of energy obtained from food.
These subnivean-dwelling small mammals include various species of mice, voles, moles and shrews. Small, furry, rodent-like creatures often get lumped together (“LBJ’s” or “little brown jobbers”), but each of these winter-active animals is just a little different in physical appearance and behavior.
Mice and voles are classified in the order Rodentia; they are the true rodents. They have small orange incisor teeth as do all rodents (like miniature beaver teeth). The common deer mouse and white-footed mouse look very similar, with large eyes and ears, and a long tail. They are gray/brown on top and white below. The deer mouse gets its name from its large eyes and long ears. Differences between the two species are subtle and it is not easy to tell them apart even when in hand. In the winter you may see the tracks of mice on the surface of the snow as they leave zigzagging hopping patterns across an opening before pushing under the snow at the base of a tree or downed log.
The voles are chunkier looking, have smaller eyes, rounded ears tucked in their fur, and short tails. They are reddish brown, or gray, with a gray belly. New Hampshire has a number of vole varieties, but the most common in many areas are the red-backed vole and the meadow vole. Voles in winter spend most of their time in the subnivean layer, leaving tunnels in the snow that become exposed as layers melt. Once the snow is gone in spring, you will see evidence of voles as open trenches in the grasses with piles of grass cuttings clumped together as nests. It is easy to see how common they were under the snow cover where they appeared to enjoy the freedom to move around under the insulating blanket of snow, safe from cold and predators.
Also under the snow, and more often found working through tunnels in the soil, are the shrews and moles. These are members of the order Eulipotyphla, unrelated to the mice and voles. Tiny eyes (and poor vision), small ears hidden well in the fur of their head, long pointy noses, and mostly gray fur distinguish these subnivean and fossorial (adapted for a burrowing life underground) creatures.
The Order name nicely suggests their diet: they eat mostly insects, earthworms, snails, and a variety of other invertebrates. Their high metabolism necessitates a near constant search for food to provide fuel—a shrew’s heart beats as many as 1200 times in a minute! The short-tailed shrew has venomous saliva that is used to immobilize its prey, often allowing it to store food for later use.
The fur of insectivores is short and two-directional to allow for ease of movement in tunnels. The moles tend to spend the winter farther underground, while the shrews work their way through the leaf litter at the forest floor in the subnivian layer. You may see shrew tunnels similar to vole tunnels in the snow, but much narrower, with any prints small and close together. Later in the winter or early spring, you’ll see signs of the moles as the familiar mounds of dirt where they come to the surface.
All of these critters have an important role in the environment, though most of us would rather the moles dig somewhere other than our gardens, and the mice live somewhere other than the insulation in our homes! They are near the bottom of the food chain and provide a source of nourishment for the many predators that spend the winter hunting: owls, hawks, weasels, foxes and coyotes all take advantage of these many small mammals. These small mammals also have a role in controlling insects and slugs in our backyards and spreading seeds and fungal spores. Whatever you may think of these “rodents”, they were here long before we were and they have a job to do!
Banner: In Winter Crankie artists.