WHITE-TAILED DEER IN WINTER

By John Hall

White-tailed deer survive amazingly well in the harsh weather they encounter during most Vermont winters, but they have had a long time to hone their strategies for success. White-tailed deer have existed in North America for close to 1 million years.

Winter is the most critical time of year for Vermont's deer. Deep snow and cold weather associated with severe winters invariably cause deer population declines. The longer the period of severe conditions, the greater the impact on the deer herd.

Deer have evolved several mechanisms for surviving harsh, northern winters: a substantially lower metabolic rate, an insulating coat of hollow hair, behavioral adaptations such as spending the winter in sheltered conifer stands (deer yards), and the accumulation of body fat that is used as an energy source during the winter.

Despite these adaptations, deer have a tough time making it through the winter. Dr. William Mautz, who studies deer physiology and nutrition at the University of New Hampshire, uses the analogy of deer pulling a sled up a hill and riding it down to explain what deer must face during the cold months.

In his analogy, deer pull their sled up the hill (accumulate fat reserves) in the summer and fall when they are eating highly digestible nutritious foods. The sled ride down the hill begins when winter arrives and fat reserves are used for energy. Death from starvation or malnutrition awaits at the bottom when the fat reserves are gone and vital tissues are being used for energy.

Some deer have "heavier sleds" than others (higher energy demands) and have a harder time accumulating enough fat to survive winter. Examples include lactating does with fawns (especially if there are two fawns), and fawns because most of their energy goes into their body growth.

Winter foods (hardwood and softwood twigs, needles and bark), which range from at best 50 percent digestible to completely undigestible, only serve to slow down the sled ride. In fact, winter foods are of such low quality that when winter conditions are harshest it sometimes costs the deer more energy to obtain the food than they actually get from eating it.

It is clear that deer and deer wintering areas, which comprise only 6 percent of Vermont's forest land, merit special concern. In Vermont this concern is shown in several ways. Act 250 provides deer wintering areas some measure of protection from development; the Department of Fish & Wildlife offers timber management guidelines to guard against imprudent logging; and controlled, annual harvest of antlerless deer helps prevent deer from overbrowsing and destroying their already limited winter food supply.

These important measures are helpful. They will only succeed, however, with public awareness of the habitat requirements of wintering deer and with public support for sound deer management.

John Hall is an information specialist with the Vermont Agency of Natural Resources.