The number of winter days with deep snow on the ground across parts of Northeastern Minnesota this winter is going to have a major impact on some local deer populations this year and for years to come.
We’ve been reporting the deep-snow problem for months. Now, the final Winter Severity Index numbers show several deer-management areas in the state’s Arrowhead region had numbers well into the severe category. That means a reduced or even no new fawn crop in 2020, which means a long-term impact on future population. It also means at least one more year with conservative deer harvests in many areas, meaning bucks only hunting seasons or very few doe permits.
In a normal winter about 10% of deer perish. But for some areas this winter ranked in the 10 worst deep-snow winters of the last half century. The impact is likely to be highest in St Louis County and far inland in Lake and Cook counties (Closer to Lake Superior virtually all deer migrate to the south-facing shoreline to avoid deep snow.) But parts of Carlton, Itasca and Koochiching counties also had WSI levels over 100.
“Wildlife managers will meet (later this month) to discuss antlerless harvest by deer permit area. Expect a very conservative season in 2020,’’ said Tom Rusch, Tower area wildlife manager for the DNR. “Antlerless harvest restrictions are the best way to increase deer populations over time.”
Hard-hit areas included:
The Tower area, Deer Permit Area 176 finished with a WSI of 166 (the long-term average is 115) with 114 days of 15 or more inches of snow on the ground. For many weeks there were 30 or more inches on the ground. The area also had 52 WSI points for days with temperatures below zero.
Farther northwest in the Greany/Gheen area, Deer Permit Area 177 finished with a WSI of 143; 95 points from deep snow and 48 from cold temperature.
The Eveleth area, Deer Permit Area 178, finished with a WSI of 132; 85 points from snow and 47 from cold temperatures.
The problem was made worse by a sudden warm spell in March that, when temperatures fell again, created a thick crust on the snow. That crust allowed predators like wolves to run on top while loping deer broke through, at a time deer already were weak, making escape impossible. Rusch said not only have deer perished from malnutrition but that predator kills are up as well.
Anyone who wants a simple answer on the trend toward fewer deer in the Arrowhead in recent years need only see these numbers: From 1998 to 2010 there was only one winter with a WSI greater than 150, spurring a deer population explosion even with high wolf numbers. Since then there have been five deep-snow winters over 150 WSI (at Tower) resulting in a declining deer population. Deer at the northern edge of their range can survive wolves, but they can’t thrive with both wolves and deep snow, Rusch notes.