Inside the Outdoors: Snow deepens, plot thickens for Minnesota deer
As much as we may complain about the extremes of Minnesota winter weather, the impact of cold and deepening snow is more an inconvenience than a threat. County and MNDOT plows dependably open our roads after a snowfall, so we're able to get where we need to go. A Minnesota garage is as likely to house a snow blower as it is a lawn mower, so we can clear our sidewalks and driveways with relative ease. Down-filled clothing and other Antarctic-worthy gear can be found in nearly every Minnesotan's closet. Blizzards may come and go, but we're rarely unprepared or homebound for long.
On the contrary, many of us have taken advantage of this year's near-record snowfall by spending more time aboard a snowmobile, or on skis or snowshoes. In short, though we may tire of winter, the massive amount of snow this season is for most of us just a minor inconvenience; and for some it's been a source of great enjoyment.
The positive side of an "old-fashioned winter" is not so positive for all creatures. I got a small taste of what our whitetail deer may be coping with after the latest snow event, when I attempted to deal with an unexpected domestic problem. Newly planted trees and shrubs in our yard had been given protection before the onset of winter, with plastic trunk sleeves or burlap barricades to keep the many neighborhood rabbits from making a meal of the bark and branch tips. But the deep snow has nullified those protections. The rabbits can simply walk atop the snow, which is now deeper than the height of those safeguards.
My solution was to trudge out to each of the vulnerable trees and shrubs, and fix those barriers to keep the rabbits at bay. I had the foresight to slip on snow pants and a pair of my tallest boots, but in hindsight I should have strapped on a pair of snowshoes. Once off the path, the depth of the snow was a surprise, and easily reached my knees; later it was measured at nearly 24 inches.
I was quickly reminded how much more stable a four-legged creature is than a human. The snow resisted each attempt to lift a leg for another step. The result was a wavering, wallowing path that might have been taken for drunkenness anywhere else. Only with small, slow steps was it possible to stay upright and make headway to reach those precious shrubs. Traveling a longer distance would have been daunting.
We've already been hearing that Department of Natural Resources (DNR) wildlife managers are getting the jitters about deer survival. But attempting to navigate those drifts myself brought home just how difficult the travel—and how serious this winter—could be. Perhaps more ominous, snow during the first week of March reminded us that this is typically the snowiest month in a Minnesota winter; and we're only half-way through it.
The best news is that snow depths were not extreme in December and January, so deer were able to move well between feeding and bedding areas during that time. But things began to change in February, when some parts of the state saw monthly snowfall records broken. Deer that have to travel through deep snow expend more energy and quickly burn up fat reserves accumulated in the fall. Once snow depths make travel really difficult, deer may "yard up," and remain in a more confined area where they've packed down the snow, and where movement is therefore easier. But such confinement can deplete the best food resources, leaving deer under-nourished, as well as more susceptible to both predation and disease.
Now, in mid-March, snow depths in some parts of the state have reached three feet, while others are approaching—or are above—two feet. A measure of winter's severity used by our DNR and by wildlife managers in other states is the winter severity index, or WSI. It tallies the number of days with snow depth at or above 15 inches, and the number of days with a temperature of zero degrees or below Fahrenheit at some time during the 24-hour period.
A winter in which the index approaches 180 is considered severe, with a likely loss of deer. Already some parts of the state—particularly the Northeast, or Arrowhead, region—are at WSI totals of 120 to 140. A wider area of northern Minnesota shows WSI readings of 80 to 100. Wildlife managers acknowledge that with this much snow it could be April before a spring thaw brings depths down to the 15 inch mark. This alone could add 30 points to the WSI; not counting days with temperatures that are at, or below, zero. To some managers it seems almost inevitable that it will take an extremely early spring and snowmelt to avoid winter deer losses.
The first deer to be lost are generally the smallest, the fawns of the previous spring that haven't acquired the size and strength to cope with winter's rigors. Next to be affected are pregnant does whose vigor is compromised by the stresses of poor nutrition and weather; they can lose their fawns, or the fawns born to them may be too weak to survive. In a particularly bad winter, adult deer—particularly those that are past the peak of health—can be lost, too.
It seems ironic that winters with deep snow can be a survival advantage for some creatures that share our woodlands with whitetail deer. One is the ruffed grouse, which burrows under the snow to take advantage of its insulating properties, conserving energy and minimizing the time spent feeding and exposed to predation. Whitetail deer, on the other hand, can't hide from the harsh elements. They can be forced to expend more precious energy, be deprived of the best food resources, weakened, and even succumb during a particularly severe winter.
By this point in the winter, most Minnesotans who didn't migrate to warmer climes are hoping—perhaps praying—for an early spring. The welfare of our state's whitetails as well as our own comfort may depend on it.