Good news for Wisconsin wildlife

Winter severity index data shows a mild Wisconsin winter so far in 2015-16

With winter coming to a close in Wisconsin, 2015-16 winter severity index data shows it is shaping up to be considered a mild winter, overall.

The winter severity index is a tool used by the Wisconsin Department of Natural Resources to gauge the effects of winter weather on deer survival. The index 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 zero degrees Fahrenheit or below.

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.

In Wisconsin, the average winter severity index through March 2016 was approximately 20. WSI for the record-setting winter of 2013-2014 was 149, and biologists will continue to keep an eye on winter conditions through April.

In a deer mortality study, the department found that over-winter mortality is strongly related to winter severity, and that few deaths occur during a mild winter.

“Travelling through deep snow really drains deer fat reserves and can weaken them,” said Daniel Storm, DNR research scientist.

“Relatively shallow snow throughout much of the state this winter has been a real benefit to deer.”

Each spring, DNR wildlife staff examines deer that have been struck by a vehicle - these general health assessments evaluate fat levels at numerous parts of the body and check for pregnancy.

With a goal of ten assessments per county, the department will use this information in conjunction with winter severity index data to learn more about winter’s effects on Wisconsin wildlife. With help from health assessments, winter severity index data, and other important tools, the department is able to closely monitor and manage Wisconsin’s deer herd.

This information is put to good use at County Deer Advisory Council meetings, which resumed in March.

To learn more about joining a council, visit and search keyword “CDAC.”

For more information regarding deer management in Wisconsin or the winter severity index, search keyword “deer.”

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