Whitetail Winter: Massive Losses on the Horizon?

Deep snow and bitter cold temperatures can wreak havoc on a whitetail herd. And, sadly, it doesn’t take long for Old Man Winter to knock these critters to their knees. What’s in store for this winter? Will we see pockets of deer die-offs across snow country?

If I was a betting man, I’d answer with a resounding “no!” However, I’m not a betting man, and this game has barely started. In fact, if this was a football game, we’d barely be past our first possession of the first quarter.

I took this photo on my way to the office this morning. As you can see, the deer in northeast Wisconsin have very favorable conditions right now. (photo by Daniel Schmidt)

Current Snow-Depth Conditions

How are things looking? Snow-depth wise, eh, I’d say we’re in pretty good shape across the country. Yes, there are some areas in the 20-39-inch range for snow depth right now, including parts of North Dakota, northeast Minnesota, northwest Wisconsin and Michigan’s Upper Peninsula. You can track current USDA daily snow-depth levels here.

However, the good news is that the 14-day long-range forecast throughout much of the northern whitetail country calls for relatively mild temperatures of highs in the 30s and lows in the teens and 20s. Of course, we are barely into the start of winter, and the next 12 weeks will tell the true story.

How bad does it have to get before deer start dying from winter weather? Well, it should be noted that some deer will always die during severe winters no matter what happens with snow and/or temperatures. Nutrition plays a pivotal role, yes, but overwinter habitat is essentially what makes or breaks the deal. Compounding matters, it’s difficult for landowners to help but a few local deer survive winter when it comes to habitat. And, when it comes to nutrition, that’s a whole different matter.

This Winter’s Deer Severity Index

This blog post will not go into all of those details. The point of today’s post is to remind everyone that what we view as severe is typically not even close to what’s considered severe when it comes to deer survival. The example here is the Winter Severity Index, devised decades ago by research biologist to help educate the public on what it really takes to cause massive casualties to the deer herd.

Remember these two numbers: 80 and 100. If your local severity index gets to 80, the winter will be classified as “severe,” and there will likely be some losses of local wildlife, especially deer. If it exceeds 100, then the winter will be classified as “very severe.”

Here’s a year-by-year review of the Winter Severity Index for my home state of Wisconsin. (courtesy of the WDNR)

I happen to live in one of the few states (Wisconsin) where winter severity can play a part in natural losses. However, over the past 25 years, we have only encountered two winters (2000 and 2013) that were considered severe. You might have heard your parents or grandparents lament about how things were “way worse” when they grew up, and they were probably right. From 1968 to 1998, this same region experienced 11 severe winters, including three out of four years from 1968-1971 when the non-severe winter (1969) was high on the moderate level.

So … what exactly is a severe winter when it comes to white-tailed deer survival? It’s an easy formula; one that you can track daily if you wish.

Deer Severity Index Formula

The formula consists of a simple counting exercise. For each day that you have an average snow depth of 18 inches or more, put down 1 point. Then, for each day that the low temperature is at or below 0 degrees, put down 1 point. It’s important to note that average snow depth isn’t what you measure in your yard. It’s the average snow depth for your township or county. Also, the temperature is the low temperature not counting the wind-chill factor.

As of this writing, I know of no whitetail area that has amassed any points for the 2022-2023 winter. That’s not to say, however, that it won’t happen. Again, it’s a long winter. Right now, I’d be keeping an eye on the weather if you live and/or hunt deer in northeast Minnesota, northwest Wisconsin, northern North Dakota and Michigan’s U.P. There certainly will be reason for concern for our friends to the north (Ontario, Saskatchewan, et al), as snow depths are mounting up there and the bitter-cold temps are sure to follow.

When deer do die from winter weather, there are typically many factors that lead to their losses. Click here to find out what eventually causes losses to the whitetail herd.

We will keep you updated as winter progresses, but in the meantime enjoy these “balmy” days of January. They surely won’t last!