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Inside the Outdoors: Deer flock to any feeding opportunity

Inside the Outdoors with Mike Rahn

Photo illustration, Shutterstock, Inc.

As Minnesotans wait with understandable impatience for the end of one of the longest winters in recent memory, the waiting holds more urgency for some. More urgency for wildlife, to be sure. For them, it can be a vigil with life or death consequences.

There’s little argument that the wild creature highest on the “special concern” list—certainly among hunters—is our whitetail deer. Apart from the dangers posed by predators like the Eastern Gray Wolf, and the all-too-real risk of injury or death by collision with a motor vehicle, winter is always a force that can play the role of grim reaper.

To a great extent, a whitetail’s probability of surviving a Minnesota winter is a numbers game. In this case, the numbers are part of an equation biologists use to gauge whether a winter is severe enough to cause deer deaths by starvation, or weaken them enough to be vulnerable to predation. The equation is the Winter Severity Index, or WSI. It’s not “new math” by any means, but simple addition: the number of days with snow depths of 15 inches or more, added to the days when the temperature drops to zero, or below.

If the total by the time winter breaks is less than or equal to 50, it’s considered a mild winter. If the WSI is 120 or more, the winter is considered severe in terms of deer survival. In the range between these two extremes, the effect of the winter on deer survival is a facts-and-circumstances thing. One thing that is clear, however, is that a substantial part of Minnesota is now in the severe range, and—especially in the north—it will be days, perhaps weeks, before snow depths drop below 15 inches.

Deep snow is such a negative factor because it restricts deer mobility. That mobility is key to deer remaining well-fed under conditions that are more draining of their energy than any other time of year. Mobility is also key to their staying one step ahead of predators. Severe winters are especially hard on young and small deer, the older and less fit, and can also impact the ability of pregnant does to bear healthy fawns.


There are some rays of hope, however. Literally. Although it will be many days before there is bare ground in most areas of northern Minnesota, the more direct rays of sunlight now can have a powerful effect, especially in some limited but important places. Such places absorb the sun’s rays and can actually melt the snow pack down to bare ground, even while snow lies deep just a few feet away. It’s to such places that winter-weary deer gravitate.

My wife and I regularly drive a rural road between home and a scenic spot where we take daily walks, and occasionally stop at a pub-restaurant nearby. These short drives take us past several large parcels of woodland. Some of it is Norway pine plantation, others a blend of mixed-age conifers and deciduous trees; birch and aspen, mostly.

Along the south-facing sides of these parcels we’ve been finding narrow bands of bare ground. Not bare, actually, but barren of snow, revealing last year’s growth of grassy cover at these sunward-facing woodland edges. It’s clear that the sunlight absorbed by the trees’ trunks and the needle-clad branches has generated enough warmth to gradually melt the snow there. On these daily drives we’ve acquired the habit of counting deer, which we often see either grazing on the snow-flattened, tawny brown grass or bedded down and “ruminating,” also known—in farm animal terminology—as “chewing their cud.”

It would make sense that deer could get more nutrition out of new, green grass. Unfortunately, that is not available just yet. But deer, like cattle, have digestive systems that can digest cellulose, a plant fiber that is just as available in last year’s grasses as it would be in a bale of hay we might feed to a Holstein or a black angus.

On one of our more memorable deer-count trips past these parcels of woodland, we counted 25 in a stretch less than a half mile long. If we had been driving past a captive deer farm somewhere in Minnesota’s Southeast region, we would not have expected to see more! All of which made perfect sense: winter-weary deer taking advantage of one of Nature’s overdue generosities.

All of this made perfect sense. What made less sense, and seen on the day preceding April Fool’s Day, was a pair of sandhill cranes fast-stepping their way across the road and into a snow-drifted cattail margin that surrounds a pond near our home.

Sandhill cranes are dietary generalists, feeding on grains, seeds, insects, reptiles, amphibians and even small mammals, like mice or voles. Just where this pair of cranes will find these things—with lakes and ponds still frozen, and fields still covered in snow—is anyone’s guess. Perhaps—we can hope—they have inside information on an impending rapid thaw! That, or some a feeding strategy I’m not imaginative enough to guess at!


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Mike Rahn, columnist

Opinion by Mike Rahn
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