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Meadow Vole

Tunnel Vents

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Frequently you find a hole about an inch wide in the snow in the middle of a field, with no tracks going in or coming out of it. Logic tells you it leads to the subnivean layer – where the snow, warmed by the ground, sublimates into water vapor, creating a small space between the surface of the ground and the snow where the temperatures is relatively stable at 32 F. It is here that small rodents such as mice and voles create a maze of tunnels through which they travel from their sleeping quarters to feeding stations, undetected by many predators.

However, the lack of tracks into and out of this hole indicates that it is not an exit or entrance to the subnivean layer, but rather, it is a vent leading from the subnivean tunnels to the surface of the snow. Carbon dioxide from animal respiration as well as carbon dioxide released from the ground builds up to an unhealthy level in these tunnels. The holes we see in the snow are ventilation shafts, allowing the carbon dioxide to escape from the tunnels. The formation of crystals around the edge of the pictured vent indicates that warm, moist air from rodent lungs is rising up out of it.

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Puzzling Kill Site

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Close examination of the bits of fur scattered over a 15-inch-diameter patch of snow reveals that the animal to whom the fur belonged was very small and would have appeared brown to an observer. (The hairs are black, but they have a brown tip.) This eliminates gray/black shrews and moles, leaving a white-footed mouse (due to habitat) or a species of vole (most likely meadow vole) as the victim. Striped skunk tracks led to the remains of this rodent, which is not surprising, as mice (Peromyscus sp.) and voles (Microtus sp.) are high on their list of preferred vertebrates. What is puzzling is why the fur wasn’t consumed and why so many of the internal organs (top of photo) were among the discarded fur. A skunk would neither skin nor eviscerate its prey. Explanations welcome!

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Meadow Voles Soon To Begin Breeding

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Under perfect conditions, with no predators, no deaths and abundant food, a pair of meadow voles (Microtus pennsylvanicus) could produce a million descendants in a single year. Because they are prey for nearly every meat-eating animal that exists, however, their population, while large, is nowhere near this.

Even though the number of meadow voles is relatively high and they are active day and night, year round, it is unusual to actually set eyes on one. What we do find, especially this time of year, are meadow vole signs in the snow: mazes of runways on the surface of the ground that are exposed as snow starts to melt, air-exchange holes originating in their tunnels and extending to the surface of the snow, tracks and entrance/exit holes to their tunnels.

The social behavior of meadow voles is about to undergo a seasonal change. During the winter, when they are not breeding, meadow voles are more social and commonly share their nests, probably to conserve heat. In another month, however, as breeding begins, females become fiercely territorial towards other females, and males are aggressively establishing dominance over each other. The peaceable subnivean meadow vole kingdom is about to come to an end. (Thanks to Susan and Dean Greenberg for photo op.)

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Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.


Meadow Voles Food for Coyotes

1-11-15 coyote  192When there is deep snow on the ground, white-tailed deer are often preferred-eating for eastern coyotes, with snowshoe hares not far behind. While small rodents are also consumed during the winter, they make up a larger proportion of a coyote’s diet during spring, summer and fall. With only a few inches of snow on the ground currently, meadow voles are still very vulnerable to predation, as the tufts of grass where they tend to nest are still visible.

Tracks indicate that a coyote stopped to investigate numerous grass tussocks scattered throughout a nearby field recently. Near several of these clumps of grass were slide marks (see foreground in photo) where the coyote had jumped, landed and slid. The groove made by the coyote’s sliding foot always ends with a foot print. At this particular site, the coyote had pounced, slid and then dug and uprooted a nest, possibly procuring a vole, but leaving no trace of success behind. What it did leave behind was scat (3 o’clock in photo), with which the coyote claimed ownership of the site.

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Meadow Vole Nests

meadow vole nest  089Meadow voles (Microtus pennsylvanicus), tiny mouse-like rodents, spend a majority of their time on the surface of the ground, particularly in moist fields filled with grasses and sedges. They have elaborate runways through the vegetation – well-worn trails about the width of a garden hose which they keep mowed down with their incisors. Latrines of small brownish-green pellets can be found intermittently along the trails.

Most meadow vole nests are constructed out of dried grasses, also on the surface of the ground, although they are sometimes built at the end of shallow burrows. When above ground, the nests are often located in the center of a grass tussock, where they are less apt to be flooded. When there is snow on the ground they are a bit easier to find, as the heat of the voles inside the nest melts away the snow, forming a chimney that sometimes reveals the nest below.

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Good Winter For Meadow Voles – Not So Much For Woody Plants

4-16-15  meadow vole sign 009Warming temperatures have revealed the considerable amount of activity that occurred under the protective deep layer of snow this past winter. In addition to a multitude of exposed meadow vole runways, there are ample signs of the voracious appetite of this small rodent. Given that more than 90% of a meadow vole’s diet consists of vegetable matter, that it can eat more than its own body weight in 24 hours, and that it breeds throughout the year, it is no surprise that the bark of many woody plants was consumed this winter, resulting in much girdling, and thus the demise, of many shrubs and saplings.

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Meadow Vole Tunnels Exposed

3-31-15  meadow vole exposed tunnels IMG_3528If you live where the snow is actually melting, a labyrinth of vole tunnels may be revealing itself to you. These tunnels were excavated in the snow next to the ground in what is referred to as the subnivean layer. They lead from sleeping areas to known sources of food, and are advantageous to both mice and voles that travel in them – they provide thermal insulation by protecting them from the wind and cold, and they keep these rodents hidden from predators. Carbon dioxide, which builds up in the subnivean layer from animal respiration as well as CO₂ released from the ground, escapes through ventilation shafts, or air vents, that lead up to the surface of the snow.

Voles stay in these tunnels as long as the snow is deep enough not to expose them, finding food in the form of plants, seeds and bark from bushes and shrubs as they dig through the snow. This winter has provided voles, mice and shrews with an extended period of protection, as hungry barred owls attest to.

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