Several years ago in the late December bow season, I watched an old buck pick his way slowly through a corn-stubble field.  He was a big-bodied deer, but obviously he’d been through the rutting wars.  He never came within bow range, but came close enough for me to see through my binocular that he had suffered two bad wounds.  First, he had lost an eye, probably while fighting over a doe.  He also had what appeared to be a deep puncture wound at his front shoulder, which resulted in a pronounced limp.  This guy wasn’t in the best shape, and he still had to face a very harsh winter.  Would he make it, I wondered.
Breeding bucks really abuse their bodies during the rut.  They fight and sometimes receive serious wounds from their adversaries.  Of course, they also chase does for days and don’t take time to eat.  In fact, breeding bucks lose up to 25 percent of their body weight during the rut, a time when sex is more important than food.  I had a fraternity brother like that years ago, but that is another story.

We know that bad winters kill lots of deer, especially where deer populations are high and habitat is overbrowsed, such as in areas of the far North.  One or two bad winters can really decimate a herd there.  For example, the harsh winters of 1995-96 and 1996-97 killed more than 300,000 deer in upper Michigan.  In other northern areas, winter mortality is all part of the game.  In Manitoba, between 5 and 15 percent of all deer die each winter.  If you’ve ever hunted deer in the cold month of November in Canada, it makes you wonder how any deer survive the really brutal January-through-March period.  But they do.
Throughout most of the whitetail’s range, the rut ends about the time that winter cranks up, so bucks don’t have much time to recover their weight and health.  This leads to the obvious question of whether hard, bitter-cold winters kill our best breeding bucks.  Not necessarily.
Research shows that deer utilize several adaptations that allow them to survive the harsh winter weather.  They lower their metabolic rate and lose approximately 20 percent of their body weight.  In the North, they seek the warmer south-facing slopes and they get out of the wind and take refuge in dense conifer stands.  They don’t move much and spend a great deal of time bedded down.  All of these adaptations conserve energy and reduce the loss of what little body fat they have.
Research also shows that good nutrition is critical to deer survival in winter.  Deer might get as much as 40 percent of their daily winter energy from fat tissue, so the amount and quality of food they consume in the fall can determine how they’ll fare during the winter.  Plain and simple, to make it through bad winters, deer must build up fat in the fall.  Once winter snows hit, deer have more trouble finding food.  Obviously, croplands can provide good gleanings, but deep snows might force deer to feed on browse and, in many areas, winter browse is limited.
The Fate of Fawns and Older Bucks
Back to the original question: Are some deer more vulnerable to harsh winters?  Most research shows that fawns, including button bucks, are the first to go in bad winters.  In fact, as much as 80 percent of all winter mortality involves fawns.  Their smaller size doesn’t allow them to compete for limited food resources and, as a result, they starve.  Smaller deer do not retain body heat as readily as do bigger deer, though male fawns have an advantage here because they weigh more than female fawns.
Bucks and does over 7 ½ years of age are also hit hard by winter.  What about our breeding bucks, between 3 ½ and 6 ½ years of age?  It appears that they make it through most winters fairly well.  Those living in the farm belt seem to get along just fine, for the most part.  Food is available, so most of the older bucks can keep themselves stoked with calories.  Of course, some die, but injuries play a bigger role in their mortality than do snow and cold.
A study conducted on a military base in Oklahoma showed that 72 percent of all buck mortality took place during and immediately after deer-hunting season.  Mortality during the winter was not high.  What about areas where the winters are mild?  Dr. Charles DeYoung and Dr. Mickey Hellickson provided some clues there when they studied buck mortality on some ranches in south Texas.  The winters there are mild compared to the winters farther north.  On many south Texas ranches, bucks are protected until they are 5 ½ years old — so there is a higher percentage of older bucks in such areas — and droughts in the region are fairly common and result in poor feed.  DeYoung and Hellickson found that male fawns, yearling bucks and bucks 7 ½ years old and older were most vulnerable to natural mortality, especially in January and February.  Death resulted not from cold weather, but starvation due to poor feed.
When stressed bucks enter the cold days of January and February, predation can also be a problem.  The south Texas study determined that coyotes played a major role here.  My guess is that wolves are also a problem for deer in northern Minnesota, Michigan, Alberta and Saskatchewan.
The bottom line on winter mortality is that if the habitat is in good shape, most prime-aged bucks will survive winter, regardless of how badly they abuse their bodies during the rut.  Other deer will do better when good fall feed is available to get them fat and healthy before winter.  It’s easy for hunters to look at forested areas and say, “we need more deer.”  However, go to that same area when there are a couple feet of snow on the ground and check out the amount of food available to deer.  In many instances, there just isn’t much there for whitetails to eat, and it is this critical period of the year that determines the carrying capacity for deer.  With good nutrition and habitat, breeding bucks do fine in winter.  With poor, over-browsed habitat, winters can be deadly.
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