Naturespeak A naturalist's view of the world

March 11, 2010

Meadow Mouse Mazes

Filed under: Uncategorized — wykes @ 9:34 pm

As the snow slowly recedes due to the recent onslaught of warm late winter temperatures, two things start to become apparent. First of all, human folk enter into a prolonged state of clothing confusion. Not knowing what to wear on a 42 degree (Fahrenheit) day, otherwise sane people walk about in sleeves and shorts next to others garbed in winter coats and knit hats while wearing sandals. (This discussion doesn’t apply to teenagers, by the way, due to the defining word “sane”).  This seasonal dementia is often accompanied by overly hopeful proclamations about spring and greatly exaggerated stories about the death of old man winter. The second thing that happens is that those secret winter tunnel systems used by Meadow Voles are now being exposed for the world to see.  I’ve not much more to say about the first phenomenon, but we should spend some time with the second because we only have a small window of opportunity to discuss it.

Meadow Voles, or Field mice, have often been the subject of death and destruction talk on this blog. I can’t count how many times I’ve referred to them as “food”, “prey”, or “victims” because, as a species, they are collectively “born to be eaten” by predators.  Right now, however, we have an opportunity to sneak a peek at the living breathing life a vole without having pieces of a dead one in hand.  We can see evidence of their behavior written on the grass.

One of the habitual traits of these grass-eating mice is to construct so-called surface tunnels through dense grassy habitat.  These tunnels are above-ground passageways that wind through the dense stems and around the clumpy growth. The vole creates these narrow passageways by literally eating through the stems and/or pushing them aside.  As the mice zoom back and forth along these inter-grass highways their repeated use eventually tramples the floor down to a mix of bare dirt and grass clippings.  These passage routes are purposely constructed so that they are hard to see from above – they are intended to be “no prey” zones. The mice live their short little lives completely within this sealed tunnel zone like tiny little bubble children (I’m not sure what that means either, but it seemed like a strangely wise thing to say).

The density of voles within any given field area can be phenomenal and their highway building efforts can have a great impact. One small study estimated that a single acre might contain as much as 4.6 miles of tunneling. Fortunately these mice don’t mind being in the company of others of their kind and have been known to gather into communal nests in the winter.

Winter also provides Meadow Mice with an opportunity to expand their narrow home lives and exploit the lush and grassy suburbs adjacent to their weedy homelands. Under the cover of deep snow, they are able to lay out protected routes onto nearby short grass areas. These places lack cover but offer a rich harvest of tender shoots.  The markings that are revealed when the snow melts are the bottom halves of what used to be completely covered tunnels (the top half was snow, in other words).

As you can see in these views, the snow systems are very complex, indeed. These intricate paths weave around and cross each other so tightly that any individual vole is likely to run into his own butt while turning a corner.  One of the tunnel systems (see below) had a long trapezoidal run to to two distant corners and an equally long return route. I can offer no explanation for this feature other than being a jogging track of some sort.

Within the runs you can see regular latrine stations where the mice stopped to “rest” (see below).  It is worth noting that Meadow Voles don’t just crap everywhere they go – they actually restrict this activity to designated toilet rooms. Since their diet consists entirely of bulky green vegetation they need to eat up to 60% of their body weight per day in order to keep up. True, they only weight 2 ounces, but that is still a significant amount of eating and pooping to do. Put that into human terms and you’d be spending a significant amount of time on the porcelain throne trying to make room for more.  Why I’d have to eat 100 lbs. a day in …order… to …never mind, that can’t be right. No, I must have the math wrong, but my point should be well taken anyway.

Actually, the reason Meadow Mice need to eat so much is because plant fibers are notoriously hard to break down. One time through the digestive system isn’t enough to derive all the nutrients. Because of this, voles count themselves as members of the coprophage society. This means they eat their own feces and run them through again! When you think of it, this is also a great way to save on space within their living quarters – the bathroom and dining room are the same room.

Concern over people wearing sandals in late winter is obviously a minor issue when compared to things like this.

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