Critters of the Subnivium

This is a picture of the paths when access to the subnivium is lost. Subnivean travel is common for both Shrews and Moles. The alternate walking pattern in the lower right comes out of a tunnel and is most likely a shrew. The track entering the top center of the photo and exiting at the bottom center is most likely a mouse traveling over the top of the snow.

The subnivium?  What in blue blazes is the subnivium?  Is that some far-off place in the wilds of Lubec?  Not necessarily.  The subnivium is the seasonal refuge that occurs at the snow-ground interface.  The snow is a good insulator so the temperature in the subnivium is usually pretty stable and not too far below freezing.  If your backyard is covered with a few inches or more of snow you have your own little refuge, and when the snow melts in June, even if you don’t live in Lubec, you might see evidence of the critters of the subnivium.  This evidence may be a network of trails leading to and around various places like a rock wall or a pile of rocks, wood or compost.  The construction engineer is usually the Meadow vole, Microtus pennsylvanicus.  This family is very prolific, and Mrs. Meadow Vole can have over a dozen litters a year.  They eat almost anything, from tree bark to lily bulbs, and are active all year.  Although Mr. Vole is very defensive of his territory, he may at times be visited by his lazy cousin, the Gappers Red Backed vole.  This handsome vole doesn’t often make his own trails, but generally uses the trails of others and is not above helping himself to anything edible he can find.  If the yard borders on a swamp the Southern Bog lemming may drop in for a look see, although these fellows are pretty rare.  If there are trees and outbuildings around, our friend the Deer mouse might use the trail system for a short cut or just explore the neighborhood.  Now these animals don’t necessarily get along, but the visitors usually aren’t looking for a fight, unlike the very distant relatives, the shrews.  We have five species of shrews listed here in the Quoddy region; the Masked, Smokey, Pygmy, Water and Northern Short-tail shrews.  Shrews, although they are listed as insectivores, are not above adding a vole or any other small animal (such as another shrew) to their diet, and storing the remains in any handy tunnel in the subnivium.

So the subnivium can be a pretty busy place, and quite well protected from the weather and most predators, like weasels and cats.  Some predators, like owls and foxes, can hear some of what’s  going on in the subnivium, and, if the snow is light and fluffy, make a successful attack on one of the inhabitants.  Our snow here usually doesn’t stay light and fluffy very long, but compacts and hardens to add an additional level of security to the critters of the subnivium, and makes the attacks of the would be predators useless.  However, weather patterns, like an extended January thaw, can be very dangerous to the denizens of the subnivium.  If the snow largely melts, it still may leave pockets of protection, but travelling between these isolated pockets can be very dangerous indeed.  The danger is compounded if an ice storm and/or dusting of snow follows, forcing the dark rodents or shrews to venture for food exposed to the elements and the sharp eyes of any hungry carnivore.  This type of weather pattern seems to be worsening, and may tip the balance more in favor of the predators, and force the critters of the subnivium to evolve or lose the race for survival.  Nature is always changing, and even though some members may be pressured, it does give us would- be naturalists a little addition to our outdoor classroom with a new problem to try and figure out who and what are making those tracks.

Note the tiny eyes and absence of ear conch. The tail is less than 1/4 of the total length of the animal, most likely this is a Short-tailed Shrew (Blarina brevicauda).