New Years is a time when many people contemplate shedding those extra pounds gained between Thanksgiving and Christmas. For numerous forms of wildlife, late autumn through winter can be a protracted season of weight loss, however, this is the result of shortages of food during these bleak months, rather than any conscious effort to become trim.
For the meadow vole, a weight loss phase of its life begins in mid autumn, causing this common rodent to lose more than a quarter of its body mass. This natural reduction in the intake of food is triggered by a specific decrease in the amount of daylight, known as photoperiodism, and typically occurs regardless of the availability of items to eat.
The meadow vole is a small, dark gray rodent often mistaken for a mouse when seen scurrying through a patch of dense vegetation. Unlike a mouse, this creature has a short, stubby tail less than half the length of its body, small rounded ears, and an oval-shaped head rather than a pointed snout. As its name implies, this critter strongly prefers to inhabit fields and meadows, which are most often found in the Adirondacks beneath power lines, in the rough alongside golf course fairways, and adjacent to roads. In agricultural meadows, this vole has been shown to be more abundant during times of its peak population than any other mammal, as its numbers can exceeds those of both mice and shrews.
As cool weather becomes the norm, and daylight decreases beyond 11 hours, the appetite of the meadow vole begins to wane, and several physiological changes start to occur within its body. Perhaps the most important is the drastic decline in the production of sex hormones, which brings an end to the prolific breeding activities responsible for its high population density. Under good conditions, a female bears at least a half dozen litters in our climate each year with most litters containing from 4 to 7 babies.
Additionally, young voles develop rapidly and become sexually mature in just over a month. This allows the first 3 to 4 litters of the year to begin bearing babies of their own that same summer, which can cause a population to swell, especially in the absence of many predators. In the Adirondacks, there inevitably are an array of creatures ranging in size from the short-tailed shrew to the coyote that prey heavily on meadow voles, and this tends to keep the numbers of this rodent in check with its surroundings.
The elimination of the urge to mate at this time of year greatly reduces the hostility between members of the same sex. It is this urge to drive away rivals that is instrumental in the formation of individual territories during the breeding season. Without this animosity, several neighboring individuals become inclined to gather into a single nest during the start of winter in order to share body heat, thereby maintaining a suitable internal temperature with a minimum of food oxidation. Also, by eliminating fighting over territorial boundaries at this time of year, energy is not wasted on physical confrontations, and there becomes a larger number of undisputed areas over which these critters can forage. Additionally, by restricting the amount of time that a vole spends searching for food, it reduces the opportunities that it presents to its many predators which become aware of its presence as it travels on the ground under the snow.
Even though a meadow vole may restrict its movements to its network of inch and a half diameter tunnels that it develops in the subnivean environment, many predators still have the ability to detect its movements and extract this rodent from its icy surroundings.
Periodically, meadow voles come to the surface of the snow for short excursions in the world of fresh air and natural light. This is when they become the target of owls which are unable to dig through a layer ice crystals or a substantial accumulation of powder as can a fox, coyote, fisher, or bobcat to capture a vole. Some naturalists believe that a vole must periodically venture to the surface in order for its brain to get updated information on the lengthening of daylight.
In our region, it seems that as daylight again approaches 11 hours in duration, this rodent quickly regains its former appetite and increases its intake of food, if it is able to find adequate items to consume. This typically corresponds to late February, a point in time when most humans have long since abandoned their resolution to shed those extra pounds.
Because of losses through predation throughout winter, most central nests that housed a half dozen adults or more now only contains one or two individuals. If both surviving voles are members of the opposite sex, they eventually mate and begin the process of repopulating that open setting with more meadow voles. Should all of the survivors be of the same sex, they all eventually disperse to separate, nearby sites to establish territories of their own. (Winter nest are not typically situated in places where breeding nests are located.)
Dieting can be a great endeavor for humans wanting to achieve a more healthy weight. For the meadow vole, dieting is a practice brought on by decreasing daylight which brings about changes that helps these critters better survive the rigors of winter here in the Adirondacks.
Photo: a young meadow vole. Courtesy Wikimedia user.