Some deer will die as winter snows pile up
If you've screamed uncle after shoveling in recent weeks, just imagine what the Northland's whitetail deer are going through.
Snow on the ground is a yard deep in some parts of northeastern Minnesota, the snowiest region in the state. And even if it stopped snowing now, it's likely some fawns, bucks and even some previously healthy does will perish by spring.
Snow depths last week ranged from 38 inches on the ground 7 miles north of Two Harbors; 32 inches near Island Lake north of Duluth; 31 inches at Wolf Ridge near Finland and at Cohasset; to 26 inches at Cloquet and Isabella. Duluth officially reported 24 inches on the ground, down from 27 inches earlier in the week as the snow settles.
The Minnesota Department of Natural Resources winter severity index awards one point for each day with 15 inches or more snow on the ground and another point for every day below zero.
An average winter severity index in northern Minnesota is 115 by the time the snow melts below 15 inches and the last subzero days are past. The DNR says that number leads to about a 10 percent die-off of deer.
But this year will be worse, said Tom Rusch, DNR area wildlife manager in Tower covering a large portion of the Arrowhead region. Rusch said the DNR's winter severity index already has hit 100 in his area with several weeks of winter yet to go.
"You can see the deer really struggling to get through the snow. Especially the fawns,'' Rusch said. "It's getting worse for them with every snowfall."
Rusch said snow depth, especially the duration of deep snow, is the most important factor in deer winter survival in northern Minnesota. Cold weather is less of an impact, although extreme cold can cause deer to burn critical fat reserves faster.
Rusch estimates the WSI for his area will hit at least 145 and maybe 150 or higher by the end of this winter. That's considered a hard winter and will lead to higher than average deer die-off — more than 10 percent.
"Even if we say that we're almost done with the extreme cold, the snow we have isn't going anywhere through March or even into early April,'' Rusch said. "By the end of winter it (the WSI) is going be right up there with some of our tough winters."
Severe winters can impact herds when young, old or under-nourished deer can perish and when does can have fewer or no fawns the following spring because their winter nutrition isn't good enough. Fawns and mature bucks (stressed from mating last fall) are the first to go, followed by previously healthy does.
Anything around 180 is considered extremely severe when as many as half the deer in an area may perish, Rusch said. The worst winter severity index in recent years was 212 in 2014, a winter that knocked-down deer numbers across the region to the point it took several years for deer numbers to recover.
But Rusch said the one-two punch of a 202 index in 1996 and a 162 index in 1997 had the most devastating impact on the northeastern Minnesota deer herd. That's when one study showed 40 percent of adult does died. It's likely a much higher percentage of fawns and bucks died then, Rusch said, and it took several years of mild winters for the herd to rebound.
While moose have long legs and are built to withstand current conditions, deer — which moved into the region over the last century — are not. Deer do seek out protected areas in cedar swamps, along the south-facing North Shore, and other areas with less snow. But deep snow makes it difficult for them to move around and find food. It also makes them more vulnerable to wolves.
"We're on the very northern edge of whitetail range. This (hard winters) has always been a factor,'' Rusch noted. "It's very difficult to keep high deer numbers up here with our occasional hard winters and predators like wolves."