White-tailed deer in northern climes must deal with winter almost six months of the year including the brutal January conditions. How do they do it?

Winter hits hard and early in the northern reaches of whitetail country, and it hangs on for a long time. Sometimes bucks aren’t even out of the rut when snow starts accumulating in November. By the end of the month, cold can hit, too — a real, below-zero kind of bitterness that digs deep and won’t let up.

By the time autumn officially ends on December 21, the winter solstice, whitetails may have been dealing with challenging conditions for a month or more. If the deer had a good fall and fattened up well, December doesn’t bother them much. But they’re really only just getting started on their season of survival.

January — a month unto and of itself, the true depth of winter — brings harsher conditions than December dished out. The days might be noticeably lengthening by the end of January, but meteorologically speaking, the sun is at its weakest for the year. Dry, intense cold grips the land … in between blizzards, clippers and three-day- long snowfalls.

February gets worse. Limited forage becomes harder to find and get at. This is when fat reserves whitetails built up during the past fall really start burning up. An occa- sional rain might fall, followed by deep cold that freezes a crust over the snow, making deer use inordi- nate amounts of energy when they try to move about.

By March, a few sunny days and perhaps some above-freezing temperatures offer a glimmer of hope that winter won’t last forever. But March can deliver sub-zero cold. And it’s also the snowiest month, providing more accumulation to tack onto an already staggering snowfall tally.

Then April turns. Though the spring equinox might have already passed on the calendar and in the skies, April can well be the meanest month of all. It is spring in name only. Whitetails are at their weakest and most vulnerable after months spent fighting cold and snow. But winter lingers, and fierce snow storms are always a possibility in the wet, cool and unstable conditions of an atmosphere between seasons. These conditions can put whitetails over the starvation edge.

Six. That’s how many months of the year Northern whitetails must deal with the elements of winter. Half the year. How do they do it?

Like most natural processes, the simplicity and elegance of the white-tailed deer’s wintering strat- egy is precisely what makes its adaptations and behaviors so successful. Let’s look at the Northern whitetail’s winter survival formula and see just how deer go about beating this potentially killer season.

Dual-Strategy Coat
During early fall, whitetails exchange their light, thin and summery red coats for heavy-duty winter garb. Deer grow a short and dense undercoat of wooly fur, then top it with stiff, hollow, long and dark guard hairs on top.

This dual strategy addresses two key needs during winter. The wooly underfur, next to the skin, provides excellent insulation and heat retention, while keeping cold air away from the body. The hollow outer hairs trap body heat that might escape the underfur. Whitetails often erect these long guard hairs during winter to assist in this function; this is why deer often look bigger and “fluffier” during winter.

In addition, on sunny days the guard hairs’ dark color can absorb the sun’s rays and help warm a whitetail.

Building Fat Reserves
Food becomes scarcer and harder to get as winter wears on. That’s why during fall, whitetails build up dense body fat reserves to draw upon during lean times. When you field-dress a deer, you can see the white fat globules inside its body cavity. When you skin a deer, there’s the waxy layer of fat reserves deposited over the deer’s back and rump; while they last, these particular fat deposits also provide a measure of insulation.

Fat is the most critical element of the whitetail’s winter survival formula. Unless there’s a rare mild winter, a deer without extensive fat reserves is a deer in trouble. In fact, fat is so important that by mid-autumn, white-tailed fawns will shift to putting on body fat instead of growing taller or adding muscle and body mass.

If forage was good all fall, does go into the winter with the best fat reserves. This is important because they are carrying next spring’s crop of fawns. Relatively speaking, fawns carry more fat into winter than do bucks. Run down from the rut’s rigors, bucks can be at risk if winter hits before they’ve had a chance to put some fat back on.

Metabolism
As winter begins, Northern deer remain active — on the move, look- ing for food, and for some, migrating anywhere from a few to 30 or more miles to wintering areas.

Conventional wisdom would say that a mammal’s metabolism should increase as cold weather intensifies — the better to create heat and stay warm. But a whitetail’s metabolism actually slows to low gear, and then to a crawl, as winter progresses.

Why would metabolism — defined as the rate at which a body burns calories to maintain basic functions — decline now? Instead of burning more fat to stay warm and compensate for the cold, lower metabolism makes a whitetail’s body exceedingly stingy in the way it expends energy.

Now, the colder it gets, the more whitetails will just bed down and stay put. When snow is difficult to traverse and the temperature has bottomed out, any energy expended obtaining the meager food available would far outpace the calories gained.

Studies show that a whitetail’s metabolism can drop by half during the depths of winter. Consequently, deer might only venture out to feed once a day. If conditions are especially brutal, whitetails will hole up for days at a time, using fat to fuel that lower metabolic rate and come out ahead. For now.

Size Matters
Northern whitetails grow big for a reason. Ecologically speak- ing, a large body means there is less surface area relative to total body mass, so the deer produces heat more efficiently and retains it better. In biological circles, this is known as Bergmann’s Rule. Large size also benefits whitetails when they have to fight the elements and push through snow.

It’s important to have that size going into winter. A whitetail in April can weigh 25 to 30 percent less than it did during late November.

Yarding Up
During winter, whitetails prefer to bed in places that are out of the wind and, if possible, that offer thermal cover overhead. Conifer swamps (chiefly cedar, fir, spruce and hemlock) make prime winter bedding areas. In hardwoods, white- tails seek out the thickest, brushiest, nastiest cover they can find. On the prairies, cattail sloughs make perfect winter bedding grounds because the bent-over stalks offer overhead thermal protection.

Where agricultural food is available to Northern whitetails (usually in the form of corn, soybean or other grain stubble), and if the snow doesn’t get too deep, deer might live through winter in small groups. But deep snow and extreme cold can push even farmland deer to bunch up into big herds of up to 100 or more animals, focusing on zones where food is available and thermal cover is prime.

In the more forested areas of Northern deer range, whitetails often migrate to traditional deer yards as a matter of both tradition and survival. Yarding is learned behavior, with the location of wintering areas and routes to them, passed along from generation to generation.

The name “deer yard” conjures up images of a small place with deer packed in tightly, almost like cattle. But that’s usually not the case. Rather, the typical deer yard encompasses many acres, often
hundreds upon hundreds of them. Usually located in lowland conifers, whitetails congregate in a general area because of slightly favorable conditions that might just make the difference between life and death in the long run:

• Lowland geography reduces the amount of wind hitting the deer and sapping any heat produced.

• Thermal overhead cover helps protect deer from descending cold and helps hold in some body heat.

• A thick overhead branch network catches some snow and holds it off the ground, allowing deer to move about more freely.

During winter, every little bit counts. The environmental benefits of spending winter in a deer yard can help a whitetail preserve just enough fat to make it through winter’s last killer days.

Bedding Behavior
The way deer bed now works to retain as much heat as possible, which helps preserve precious body fat.

A whitetail bedding in the cold will curl up with feet underneath, then snuggle down in the snow for some of the insulating properties offered and to maintain a lower profile against any wind. A deer will also lay its head alongside its body. If conditions are severe, a whitetail will just stay put like this for as long as needed.

In the open prairie and Northern plains, and in hardwood areas where whitetails aren’t yarded up in conifers, winter whitetails will head to open areas to bed on sunny days. Here, on a south-facing slope with an angle that maximizes what power the sun has, a whitetail out of the wind can absorb a few rays, gather free warmth, and preserve some more of its precious body fat.

Despite all of their biological and behavioral adaptations against the cruelties of winter, some whitetails just won’t make it. That’s nature’s way: The youngest, smallest, weakest and oldest are culled out, while the fittest and strongest survive to pass on their winter-fighting abilities on to the next generation.