In the Northern Hemisphere, the white-tailed deer’s cyclic rhythms in physiology, metabolism, coat molt, reproduction, and general behavior are closely regulated by the changing amount of daylight, or “photoperiod.” The shortening day length in autumn triggers a complex chain of events that lead to the whitetail’s growth of a thick insulative winter coat, the accumulation of heavy fat deposits, breeding and various other changes in behavior. All improve the species’ prospects for surviving the bleak winter season.
In the north, especially, the timing of the whitetail’s breeding is strictly regulated by decreasing photoperiod. This ensures that fawn births occur on schedule in spring and early summer when food, cover, and weather conditions are most favorable for their survival.
Even within the continental United States, due to varying environmental pressures and resultant selective forces, the seasonal biological needs and behavior of whitetails in winter differ rather dramatically from north to south. Although the winter season may not be particularly tough on deer in southern parts of the United States, winter is still a sinister grim reaper in northern states. The combination of prolonged cold weather, deep snow cover, inadequate shelter, and poor food conditions frequently contribute to extreme hardship for whitetails.
As we’ve seen in the recent past, the annual winter death toll of whitetails in northern Michigan may even exceed that of the legal harvest by hunters.
In the north, selective pressures have favored whitetail traits that are closely linked to rhythmic, often abrupt, seasonal fluctuations in the availability of food and shelter. As one progresses northward, more and more of the whitetail’s lifetime is devoted to preparing for, enduring, or recovering from the stressful winter season.
How a northern whitetail behaves during winter, and whether or not it survives, will hinge heavily upon when it was born, how well it was nourished and grew during summer, the level of fatness it achieved during autumn, and the severity of the winter season relative to the availability of food and shelter.
During winter, deer must become ultra-energy-conservative in order to survive. Their adaptive traits for winter survival include an array of timely physiological changes, greatly reduced movement activity, shelter-seek behavior (referred to as yarding), migration, intense socialization and a host of other behavioral adjustments. These adaptive changes permit them to better cope with the pending negative energy balance and to minimize the dangers that hungry predators present.
Northern whitetails deviating greatly from these highly adaptive adjustments–generated through centuries of ancestral response to environmental stress–are less likely to survive and perpetuate alternate patterns not conducive to softening the impact of the harsh winter season.
For obvious reasons, selective pressures imposed by cold weather and snow cover are less operative in the South. There even late-born, small, and weak deer stand a good chance of surviving the comparatively mild and typically brief periods of winter.
Commencing with my studies in 1961, I’ve watched whitetails struggle to cope with unbelievable winter stress, especially as it prevails along the south shore of Lake Superior. I’ve seen hundreds of them die there during tough winters. But I continue to marvel at the fact that somehow, almost miraculously, so many can survive such hardship and deprivation.
Believe me, this critter we call the whitetail is as opportunistic as any of God’s creatures, and far more resourceful than most.
Unfortunately, deer wintering habitat in Michigan’s U.P. has not been properly managed–and there is no evidence that it will be in the near future. As a result, deer populations in this northern region will continue to decline following tough winters and rise somewhat after easy ones; however, the lows will get lower, but so will the highs.