Despite some recent springlike temperatures, and while southern Minnesota is nearly void of snow, snow on the ground remains more than 2 feet deep in parts of Northeastern Minnesota, continuing to rack up tough times for the region’s deer herd.
The problem is most serious in the state’s Arrowhead region, namely eastern St. Louis, Lake and Cook counties away from Lake Superior, although parts of Carlton, Itasca, Koochiching and Beltrami counties also had 15 or more inches still on the ground as of Thursday, according to the Minnesota Climatology Office.
Snow depth was still at more than 22 inches at Tower as of Thursday and remained above the 15-inch threshold in Eveleth and at the National Weather Service in Duluth. In the state’s heaviest snow belt, Wolf Ridge Environmental Learning Center near Finland still had 34 inches still on the ground, down from a peak of 48 inches in February, but still a lot for a deer to move through.
Fifteen inches is the level above which the Department of Natural Resources says deer have a harder time moving around in snow, causing them stress and increasing winter mortality. Minnesota wildlife biologists have for a half-century been using a simple winter severity index to measure winter’s impact on deer. Every day there is more than 15 inches of snow on the ground, and every night it dips below zero, a single point is awarded.
At the end of an average winter, the Tower area will have a winter severity index of about 115. As of Thursday, March 12, the Tower WSI already was at 144. And with 15 or more inches of snow expected to remain on the ground for several more days, with a couple more below-zero nights possible, that number will likely hit 150 or even 160 — considered a severe winter for deer.
This year, it’s been the long period of deep snow on the ground, not the cold, that’s caused deer the most grief. (December and January were actually warmer than normal, as March has been so far, which has probably helped deer.)
While moose have adapted over millennia to deep snow with longer legs, deer, at the northern edge of their range, and relative newcomers to the region over the last century, struggle to find food and shelter when snow is deep.
Deer in the Tower area have been trudging through 15 inches or more of snow for nearly 100 days, with more to come.
Deer will continue to lose fat until spring provides more nutritious food, and that could be well into May. In a normal winter, about 10% of deer perish. But in the winter of 1995-96, among the worst on record, with winter severity indices over 200, more than 40% of adult does perished, a DNR study showed.
Mortality rates for fawns and bucks were likely higher. Severe winter impacts can last for years because surviving does can have fewer or no fawns the following spring because their winter nutrition was poor. Malnourished does often have stillborn fawns (the fawns are not reabsorbed by does as commonly believed) or fawns are born alive, but the winter-stressed does are unable to produce enough milk and the newborns die.
Deer die not only due to malnutrition, but weak deer are easier targets for predators, namely wolves. A lack of quality winter conifer cover also leaves deer more vulnerable.
Another tough winter means no quick rebound for the Arrowhead region's deer herd, and that means another year of conservative harvest goals for the DNR. That means more areas of bucks-only hunting this fall and fewer areas with antlerless deer permits available.
Deer numbers in Northeastern Minnesota, outside of agricultural areas, have been lagging behind peak years since about 2014, with frequent snowy winters repeatedly restricting the population from taking off. The good news, biologists note, is that it only takes a string of a few mild winters for whitetail numbers to bounce back.