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Winter takes heavy toll on northern Minnesota deer

This winter was tougher than average for deer in northern Minnesota, especially in northeastern counties. Winter mortality and a reduction in new fawns this spring will lead to fewer antlerless hunting permits available this fall. News Tribune file photo.

Winter ended fast across most of Minnesota this year. After weeks of heavy snow and brutal, subzero temperatures in late January and February, most of March came in sunny and warmer than normal.

Duluth officially had a whopping 27 inches of snow on the ground as recently as March 10. By March 31 it was down to just 2 inches. By Wednesday it was gone.

But for deer across northern Minnesota, especially in the Arrowhead region, the winter of 2018-19 is still having an impact that may be felt for years to come.

Wildlife experts said deer mortality due to winter weather and predation will be "significantly above average'' after this winter. Deer will continue to lose fat until spring greenup provides more nutritious food, and that could be well into May.

Even more importantly for the herd, fawn production and fawn survival will be below average as adult does will be in poor physical condition due to the excessive snow depths and duration of snow cover. Subzero temperatures had some impact, too, but not as much as deep snow.

"It was a severe winter in the north. We lost deer. We are still losing deer. It's not over for them," said Tom Rusch, Minnesota Department of Natural Resources wildlife manager in Tower. "And we won't know until summer, until after fawns are born, the real impact. Will that doe have one fawn instead of two? Or will none of her fawns survive?"

For hunters, the take-away is that wildlife managers already are planning for a more conservative antlerless deer harvest in 2019 in Northeastern Minnesota — and that means far fewer doe permits for hunters and more areas where only bucks will be legal game come November. Reducing antlerless permits is the only major tool wildlife managers have to rebuild deer herds after tough winters.

"We're going to be more conservative than last year. But we won't know for a few more weeks exactly where we will fall" for antlerless permit availability, Rusch said. That will be decided by DNR staff in May.

Points added up fast

The DNR winter severity index awards one point for each day with 15 inches or more snow on the ground and another point for every day with temperatures below zero. Most of northern Minnesota remained right around the long-term average WSI of 100-115 thanks to the rapid March warmup and melt.

All stations are now officially below 15 inches of snow, and with no more sub-zero days expected, the current index numbers are likely final for the winter.

Still, the northeast corner of the state saw higher WSI numbers that approached historic "hard" and even "severe'' levels, Rusch said. Parts of Lake and Cook counties had more than 15 inches of snow on the ground from mid-December to late March, with more than 30 inches for several weeks and final WSI numbers at 150, Rusch said. Most other areas starting accumulating points after a Dec. 28 snowstorm and kept adding through the end of March.

"For much of Lake and Cook counties, and some of St. Louis, we had a really long period with more than 24 inches of snow (on the ground) and in some cases more than 30 inches. We don't give extra points for that much snow, but you know it was impacting deer. We even saw it impacting moose," Rusch said.

Wildlife managers also lamented a change in recent years in how the DNR gets its snow data means those WSI numbers probably are lower than they should be. In the past, hundreds of DNR and other agency staff would measure snow depth in many locations even in rural areas. Now, the snow report depends on far fewer measurements taken in fewer locations.

"We now get our snowfall data from the statewide (state climatology office weekly report) rather than our own agency readings. And we just don't have as many locations reporting,'' said Glenn DelGiudice, the DNR's moose and deer project leader. "We think snowfall totals are pretty seriously underestimated in some cases."

Rusch noted that deer management zone 176, around Tower, officially had a WSI of 121 this year. But he said his hunch is the actual impact of this winter will be more like a 140 WSI. That compares to an average of about 115 and a severe winter of 180-200.

DelGiudice has been studying northern Minnesota deer for more than 30 years and has seen the impact of harsh winters on the population. Abouty 10 percent of deer die during an average winter, which up north is about a 115 WSI. In some harsh winters, when the WSI hits 180 or more, the number of does that perish has hit 40 percent.

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 wasn't good. Malnourished does often have stillborns 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, DelGiudice said.

That reduced fawn crop is what really affects future year's deer populations.

Already this year DelGiudice has lost 19 of 46 does wearing GPS collars at two study locations, one in Cass County and one in northwestern St. Louis County. That's a 45 percent mortality rate and is unexpectedly high, he said. Fourteen of those deer ultimately died from wolf predation. But when researchers got to the carcases they found obvious signs of winter stress that made the deer easy prey.

"We can tell by femur (bone) marrow fat levels that these deer were in really bad shape before the wolves got to them. They become so much more vulnerable to wolf predation during winters like this,'' DelGiudice 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. In some areas hunter harvest levels still have not recovered to pre-2014 levels. But Rusch and DelGiudice 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.

"The good news is that, right after '96 we had three of the mildest winters on record and the deer population bounced back remarkably fast,''' DelGiudice noted.

But he said higher wolf numbers now may slow the recovery even with mild winters. The estimated 2,655 wolves in the state need to consume meat equaling about 15 deer per year, or about 39,000 deer annually (the actual number is lower because wolves also eat beaver and some other critters.) That compares to 150,000-200,000 deer hunters kill each year statewide.

"There's something going on out there that's impacting'' deer mortality and herd recovery beyond winter severity, he said. "There's no doubt wolves are having an impact in some areas."

NW Wisconsin winter "not catastrophic"

Winter for deer in Northwestern Wisconsin came in a little harder than the 37-year average, said Greg Kessler, DNR wildlife manager in Brule, thanks to the rapid demise of cold and snow in March.

The winter severity index average across Douglas County hit 75.That compares to the average of 70 and the severe 170 WSI winter of 2014.

"We expect a potential decrease in fawn production and some over-winter losses but certainly not catastrophic assuming we do not have a late winter storm that lingers,'' Kessler said. DNR staff are finding very few dead deer in the woods and "I have only had a couple calls from the public reporting sick, dead or dying deer."

"Based on the number of deer people are reporting seeing out feeding in fields, it appears the deer may have weathered the winter better than expected in some areas,'' Kessler added.