Deep snow is impacting Hubbard County's white-tailed deer

Erik Thorson, Park Rapids area DNR wildlife supervisor, explains the winter severity index.

Lone winter white-tailed deer in knee deep snow
Snow depth is one factor in the Winter Severity Index. Snow over 15 inches deep makes it harder for deer to find food and that increases deer mortality rates.
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The depth of snow this winter is the most important factor affecting deer mortality in the Northwoods, making it harder for deer to find food needed to survive.

Erik Thorson is the Park Rapids area wildlife supervisor with the Minnesota Department of Natural Resources (DNR).

He explained that the winter severity index (WSI) is designed to measure the impact of winter conditions on the white-tailed deer population based on two factors: snow depth and temperature.

As of Thursday, March 9, when the last WSI was released, Thorson said this area was in the mid-50s to low 60s. Higher numbers correlate with a higher deer mortality rate.

“The latest snow wasn’t factored into that WSI,” he said. “There’s a point added for each day with 15 or more inches of snow on the ground which we certainly are at now after last weekend’s snow. There is also a point added for every day below zero.”


Snow depth vs. cold

“It has been a warmer winter than last year, which has been helpful,” he said. “Still, I think snow depth is the most important factor when it comes to white-tailed deer. It’s more concerning to have deep snow for a longer duration. I think they can handle the cold, as long as they have access to food.”

When the snow is deep, he said deer tend to stay on packed trails and places with cover that reduce snow depth.

“They’re browsing on twigs and branches, for the most part,” he said. “The WSI is tied to the deer mortality index and the population. End of season values less than 50 indicate a mild winter. We’re over that level already and will continue to accumulate points until the spring. Values over 120 indicate a severe winter.

“We're not at that level yet. We’re in between, but I think the number is underrepresenting the severity of our winter, so far. We’ve had some different events with freezing rain that have caused some crusting of snow, too. Also, the sun is more powerful this time of year, so you can get some melting and crusts forming from that.

“Depending where you’re at, sometimes predators like wolves or coyotes can run on top of the snow crust and deer are breaking through. That certainly impacts white-tailed deer. I don’t think that’s widespread, but there were some areas where that was occurring.”

Thorson said the WSI only gives an indication of what deer are experiencing out in the woods.

“There has been significant snow depth from December until now,” he said. “I measured 20 to 22 inches out in the woods before the March 9 snow, and we got 10 inches or better last weekend.”

By comparison, Thorson said the highest WSI numbers in the state were in the Arrowhead region and along the North Shore.


“They have had a ton of snow for a long time and are close to 120 on the WSI over there,” he said. “I think our reading here is a little misleading this year here, because the snow depth estimates this month are probably underestimated. I think we’re at a higher number than what the model is showing because we’ve had snow kind of close to our threshold for so long, since mid-December, basically right after that storm.

“We had over 15 inches of snow then and have been just over or just under the entire winter, so far. We had quite a dry spell in January where we probably dipped below 15 inches for a while, but we’re certainly over now.”

Impact on black bears

Thorson said the weather also impacts the activity of other animals like bears.

“Generally, we say you can expect some bear activity after St. Patrick’s Day, but I think with the snowy winter we’ve had, their coming out of dens may be delayed this year,” he said.

He said a late spring would also impact the bear’s food sources once they come out of hibernation.

The DNR recommends people remove bird feeders to avoid attracting bears and store garbage and pet food in a place inaccessible to bears. Visit the DNR website for more information.

Lorie Skarpness has lived in the Park Rapids area since 1997 and has been writing for the Park Rapids Enterprise since 2017. She enjoys writing features about the people and wildlife who call the north woods home.
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