Editors Blog

How Many Deer Will Die From Winter Weather?


The author found this young white-tailed doe frozen dead in its bed. It is unknown if the deer died from exposure, illness or injury. (photo by Daniel Schmidt)

The author found this young white-tailed doe frozen dead in its bed a few years back. It is unknown if the deer died from exposure, illness or injury. (photo by Daniel Schmidt)

Will these sub-zero temperatures kill off our deer herds? How much snow pack do we have to receive until it affects the deer population? And just how many deer will die this winter as a result of cold weather and deep snow?

It will definitely kill some deer, but not as many as one might think.

The white-tailed deer is an extraordinarily resilient animal. In fact, some might say it is North America’s most resilient mammal, as evidenced in a fossilized whitetail skeleton found in Florida that dates back a mind-boggling 1.2 million years.

This week in the Upper Midwest, we have seen below-zero temps and some hefty snowfalls. In northern Minnesota, for example, they were just hit with 18 inches of snow, and it’s minus 20 this morning. That registers two points on the Winter Severity Index (WSI).

The WSI is a gauge wildlife scientists derived more than 50 years ago to track winter’s effect on whitetails. It is amazingly accurate when it comes to estimating the weather’s impact on herd survivability and spring fawning success. In short, a region is assigned 1 point for every day that includes a low temperature of below zero (not including wind chill), and 1 point for every day that has an average snow pack of 18 inches or more on the level.

Variations of the WSI are used throughout the North, and records have been kept since 1960 throughout cold-country states such as Minnesota Wisconsin and Michigan, but a WSI tally of less than 50 is considered mild; 50 to 79 is moderate; 80 to 99 is severe, and over 100 is very severe.

Since 1960, eight winters were classified as very severe; six as severe; 11 as moderate; and 15 were considered mild.

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That being said, a few “new” factors definitely contribute to lower deer numbers when combined with harsh winter weather. These include the proliferation of gray wolves; old-growth forests and the continued decimation of over-winter habitat. Wolves have a definite and immediate impact on local deer herds, and this has led to many areas of really substandard hunting over the past decade, especially in northwest Wisconsin and northern Minnesota. The over-winter habitat demise has been felt across the entire North, especially in Michigan’s Upper Peninsula, where traditional deer yards have been splintered (and forever changed) due to myriad factors.

There is no easy answer that will help us save more deer during winter. Aldo Leopold taught us these lessons more than 75 years ago. The solutions involve more long-range planning on both forest, deer and predator (namely wolf) management.

The Problem With Scientific Deer Management