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Serving Northern St. Louis County, Minnesota

Whitetails in winter

Survival is a careful balancing act for deer in the North Country

Marshall Helmberger
Posted 1/18/17

ere in the North Country, winter requires a delicate balancing act for white-tailed deer.

The combination of persistent cold, deep snow, and less nutritious browse requires deer to change their …

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Whitetails in winter

Survival is a careful balancing act for deer in the North Country

Posted

ere in the North Country, winter requires a delicate balancing act for white-tailed deer.

The combination of persistent cold, deep snow, and less nutritious browse requires deer to change their behavior and even their internal bodily functions in order to survive. It’s all geared towards one overall goal— maintaining sufficient nutritional energy to allow deer to continue to move about and maintain body heat until warmer weather arrives in the spring.

During the warmer months, when fresh, nutritious grass and other vegetation is readily available, deer thrive. But come winter, when all those nutritious foods are dead and buried under the snow, deer are forced to rely on woody browse. It may be high in fiber, but its nutritional value is limited— and that forces deer to rely heavily on stored fat reserves to get through a northern Minnesota winter.

In milder parts of the country, winter doesn’t pose much of a test for white-tails. Milder temperatures don’t require deer to burn so many calories just to stay warm. And shorter winters mean that deer elsewhere don’t have to rely on their stored fat reserves for nearly as long as they do in the North Country.

Up here, deer winter survival depends heavily on the temperature, the depth of snow, and, especially, the duration of the winter. From the start of winter to the end, deer in our region lose ground nutritionally. The longer the winter lasts, and the more fat reserves they’re forced to burn, the greater the risk that they won’t make it through to spring.

The DNR’s winter severity index is one method of gauging that risk for deer, and it’s something that wildlife managers use to help guide them as they set harvest limits for the following deer season. The index adds a point for each day that the temperature falls below zero and another for each day that snow depths reach 15 inches or greater. The higher the number at the end of winter, the more severe the winter. When it reaches over 180, as it typically does in severe winters up here, wildlife managers expect that a significant percentage of whitetails won’t survive.

Since deer struggle to take in much nutrition during the winter, it’s pretty obvious that one of the keys to their survival is minimizing their use of energy, in order to slow the utilization of their fat reserves. One way that deer conserve energy is by putting on a thick, well-insulated coat of fur in the fall. They also eat less, which slows their metabolism. In addition, they spend as much time as possible in dense evergreen cover. We know that deer tend to “winter” in places like white cedar stands, or under dense pine, spruce, or balsam fir. That’s because these places protect deer from wind, tend to have less snow on the ground, and moderate temperature drops at night. Even a few degrees each night can make a big difference over the course of a winter in terms of a deer’s chances of survival. That’s one reason that wildlife managers try to ensure that there’s enough mature evergreen cover on the landscape. They know that this time of year, cover is more critical than plentiful browse since deer get so little nutrition from woody branches.

While some folks like to feed deer in winter, it actually can pose a number of problems, particularly if you start feeding later in the season as a way to “help” deer through a particularly severe winter. During the winter, as they shift to woody browse, deer lose many of the microorganisms in their gut that allow them to digest their summer and fall fare. They’re replaced with microorganisms that help them digest the woody material they rely on in winter. Suddenly providing a deer in late winter with alfalfa or corn can do more harm than good because the deer can’t easily digest such foods. It can actually kill them. Besides, deer feeding passes on disease, may attract wolves and other predators, and often leaves deer, and people, vulnerable to car crashes as deer make their way back and forth to areas where they are being fed. The Maine Department of Natural Resources has an adage for would-be deer feeders: “If you care, let them fend for themselves.”

There are better things you can do to help deer, such as retaining mature conifer cover on your property. I’ve seen folks cut white cedar trees in winter to provide browse for the deer, but this is probably one of the worst things you can do. The short-term benefit of a few days browse doesn’t make up for the loss of the permanent dense winter cover that cedar provide.

Rather than cutting living trees, felling dead balsam fir (which we have in abundance right now due to a combination of drought and spruce budworm) can provide deer some useful browse. They don’t eat the dead branches, but the branches are typically laden with foliose lichens, which deer love.

And one other thing— try not to disturb deer in winter. They do best when they can minimize their movements, so the more we disturb deer by our presence, the more they are stressed by the winter conditions.