The winter started off fairly easy for wildlife, but the weather has taken a sharp turn toward tough conditions for most wildlife, especially deer.
The winter severity index (WSI) is a measurement gauging the effects of the winter weather on deer survival. The index was developed in the early 1970’s and is calculated by adding the number of days with 18 inches or more of snow on the ground to the number of days when the minimum temperatures were at zero degrees or below. Generally, the severity of the winter is based on the total number of points accumulated over the collection period.
Curt Rollman in Rhinelander is a DNR deer biologist. He says deer will fatten up in the warm months to coast through the winter using their fat reserves. Harsh winter weather taxes those reserves. He says they cope by yarding up..
"Throughout the winter they feed and browse and they browse on natural vegetation and then they go into things like deer yards. That's a term for an area, generally something with conifer or evergreen cover that keeps the snow less than the ground layer because it gets caught by the branches and they can move around a little bit better...."
Rollman says the severe weather is tough on the youngest deer...
"Adult deer are fairly resilient, especially adult does, but when it comes to fawns going into their first winter they're still growing and they didn't have as much time to put on those fat reserves because they're still growing. The have issues coming into the winter and they're smaller, of course, for the snow depths..."
The January severity index was in the mild range before the extreme cold and deep snow arrived. Rollman says the winter severity index will likely take a sharp turn for the worse when the February numbers are released next week.
A winter with an index of less than 50 is considered mild, 50 to 79 is moderate, 80 to 99 is severe, and over 100 is very severe. The Polar Vortex winter of five years ago was considered the most severe winter since the state began keeping the severity index.
