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The hunt is over, and those deer that made it through the season can relax until next fall, right? In reality, this perception could not be further from the truth.
By Dr. Steve Ditchkoff
The New Year generally represents a time of renewal and fresh starts xe2x80x94 a turning of the page, so to speak. In most states, it also falls right at (or near) the end of deer season. Your season is over, and the fruits of your efforts are in the freezer, on the wall and/or at the taxidermist. You have memories, pictures and stories to tell.
For some deer hunters it is a time of sadness, because it will be eight or nine months before they crawl back into a stand. For others, it comes as a relief: The constant internal battle between responsibilities at home and/or work and the itch to be in the woods is gone for another year.
Whatever that time of year means to you, subconsciously it also probably registers as a time for peace and prosperity in the deer woods. Not so fast.
Winter: The Extreme Challenge
We all know that winter can be a time of extreme challenge for white-tailed deer, particularly in Northern regions. Deep snow, frigid temperatures and dwindling food supplies combine to push deer to their physiological limit. In Southern regions, while conditions are not nearly as demanding, the winter months still serve as a nutritional bottleneck that can limit the productivity of the population.
We also know that these conditions are the most demanding time of the year for fawns, and in some situations, overwinter survival of fawns can be seriously compromised. However, what many donxe2x80x99t realize is that this time of the year is the most challenging from a survival standpoint for the male segment of the herd as well. Just because there arenxe2x80x99t any hunters in the woods doesnxe2x80x99t guarantee that those bucks that survived hunting season are going to make it to next season.
The entire year of a white-tailed buck is geared toward maximizing the probability of breeding. Everything they do, every nutrient they allocate to their bodies, is to maximize their reproductive success.
Letxe2x80x99s start with spring. In April, antlers once again begin to grow, and the timing of this is to coincide with maximum protein availability during the antler growth period. Larger antlers will translate into a greater probability of breeding success, so bucks are trying to maximize antler size.
However, body size is more important than antler size in determining reproductive success. So bucks are attempting to allocate nutrients to both antler and body growth in such a way that their lifetime success will be maximized. Throughout the summer, young bucks will put a lot of nutrients to body growth and less to antler growth, because they need to develop a body size that will enable them to be competitive with the larger males. Theyxe2x80x99ll voluntarily reduce their short term probability of being successful breeders to increase their overall probability in the long term. In other words, theyxe2x80x99ll trade a poor breeding year at a younger age for a good year at an older age when theyxe2x80x99ll be ultra competitive. Older males, intuitively knowing that their life expectancy is rapidly decreasing, will begin to maximize their investment in antler size at the expense of skeletal growth.
As the breeding season approaches during early to mid-fall (in most states), all bucks are working to maximize their body condition. The growing season is over and protein availability becomes restricted (protein is the basic building block of body tissue xe2x80x94 muscle mass and growing antlers), and bucks are looking to build fat reserves that will help sustain them during the breeding season, as well as assist with the coming winter. They are about to enter the most energetically demanding period of their lives.
Whereas the greatest energetic rigor for does is the period of lactation (which far exceeds the cost of gestation/pregnancy), the demands of mate acquisition are the most costly for males. At their peak periods of activity, males will be actively searching for mates 22 to 24 hours each day. This leaves very little time for foraging, which is an extremely time-consuming activity.
Consider how long it would take you or me to wander through the woods and fields with a pair of scissors while having to locate, clip and chew a sufficient quantity of individual plant parts that will meet our daily nutrient requirements, all while being alert for predators or hunters. The simple fact is that males lose a considerable portion of their body mass during the breeding season.
The Drive to Breed
Letxe2x80x99s consider for a moment what the breeding season means to a deer. To a hunter, the breeding season is a period of time when the opportunity to harvest a big buck may be maximized. To deer, itxe2x80x99s also a period of opportunity, the only chance each year to pass on their genetics. Now if you consider that the primary goal of every animal every year is to pass on as much genetic material as possible, the importance of the breeding season becomes apparent.
To a young buck, the breeding season is less important than to an older male. A young buck will likely have many more seasons, and in all of those seasons, he will likely be more competitive for breeding opportunities than he is now. He will definitely put forth effort as a young buck, but he wonxe2x80x99t kill himself trying to acquire a mate. Hexe2x80x99ll avoid conflicts, spend time feeding, and work to ensure that he exits the breeding season in a position to be more successful next year.
The breeding season for mature bucks is different than it is for younger bucks. The overall goal is the same (maximize breeding success), but the future is less bright. As a result, the decision making of mature males is similar to that of a poker player that is short-stacked. The time to go xe2x80x9call inxe2x80x9d is imminent. Dominant, mature males are the most competitive for breeding opportunities, and a single male might breed five or more females in a year. This means that in a single year, a highly successful male can sire more offspring than the average male does in a lifetime. In poker terms, a dominant, mature male is holding a great hand but is short-stacked. Itxe2x80x99s time to push the chips to the middle of the table and let the cards fall where they may. These males, who are 5-1/2, 6-1/2, 7-1/2 years old, or older, donxe2x80x99t have many years ahead of them and canxe2x80x99t afford not to take advantage of what might be their best opportunity to breed.
The effort they expend during the breeding season can result in severe weight loss. Studies have reported losses of 20% or more of their body weight. As a result, males exit the breeding season in very poor condition xe2x80x94 at a time when availability of quality forage is often low. The forage that is available tends to be woody, low in digestibility and suboptimal for improving body condition.
The nutritional challenges imposed by the combination of poor body condition and poor nutrient availability ultimately leads to the untimely death of many mature males. Theyxe2x80x99ve pushed their bodies past the limit where they can recover. If it had been spring or summer and there was a bounty of high quality and palatable forages, things might be different. But remember xe2x80xa6 this is late fall, or even winter.
Impacts of Post Rut Stressors
In a study I was involved in in Oklahoma during the late 1990s, we examined the impacts of post rut stressors on the survival of male white-tailed deer. We radio-collared 80 bucks over the course of three years and documented survival patterns. It was no surprise when we found that hunter harvest was the single most important cause of mortality for our population: Forty-six percent of the mortalities occurred during the six-week hunting period on that property. What was surprising was the high rate of mortality during the four to six weeks following the hunting season. We would frequently find our mature bucks dead during this period, with no apparent trauma or symptoms of distress. The only apparent abnormality for these animals was that they appeared thin.
Mother Nature vs. Man
As part of this study, we statistically analyzed the probability of deer dying due to natural or human-induced (hunting or vehicle collision) causes. What we found surprised us. The probability of a young (1-1/2 to 2-1/2 years old) male dying from human-induced causes was five times greater than the probability of dying due to natural causes. However, the probability of sub-adult (3-1/2 to 4-1/2 years old) and mature (5-1/2 years old or greater) males dying from human-induced causes was much closer to the probability of dying due to natural causes. To quantify these estimates, an immature male had a 2.7% chance of dying due to natural causes, a sub-adult male had a 12.9% probability, and an older male had a 13.3% chance of dying.
Whereas the 3-1/2- to 4-1/2-year-old males tended to die from a multitude of natural causes throughout the year (some of these causes included predation, fighting, brain abscess), natural mortality in our mature males occurred primarily during late November through early January xe2x80x94 the four to six weeks following the breeding season. These males were exhausted from the rigors of mate acquisition and simply couldnxe2x80x99t recover. They made the ultimate sacrifice in an effort to maximize their probability of reproducing.
What we donxe2x80x99t know is whether these males were successful. Were they the ones that, for whatever reason, were having incredible success that season and so pushed it to the limit? Or were they inferior relative to their counterparts and just couldnxe2x80x99t withstand the normal challenges associated with the breeding season? Did they come into the season in poor condition for some reason, or did they have poor genetics? These are all possibilities, and impossible to answer. The only thing we know for sure is that a significant percentage of the older males that had survived the hunting season, died due to natural causes following the breeding season.
7 Keys to Success
So what does this mean for you as a hunter/manager? There are a few things you can do to at least improve a buckxe2x80x99s chances of making it to next year.
1. You have the ability to decide which deer are harvested and which are not, and thereby influence the parameters of your population (e.g., density, sex ratio, age structure).
2. You also have the ability to influence the availability of nutrients on the landscape by influencing density and/or habitat management.
3. Understand that almost everything other than population parameters and habitat quality is out of your control. Predation, competition, natural accidents, natural behavior, weather, climate, etc., all have a significant influence on the deer in your herd, and this influence is significant. In other words, however much effort you expend, Mother Nature is still extremely influential the deer herd.
4. Despite our limitations as managers, there are still things we can do to help mitigate the rigors imposed by the breeding season. We can work to ensure that our bucks enter the breeding season in good condition. Keep your herd below carrying capacity and youxe2x80x99ll maximize availability of natural forages.
5. Warm-season food plots are an excellent source of nutrients for deer, but most hunters plant only cool season plots for hunting purposes. By providing high-protein forages in food plots during the growing season, you can significantly improve the body weights of your bucks.
6. Ensure that your bucks have access to readily digestible forages following the breeding season. The obvious (and simple) solution to this is to provide supplemental feed for a few weeks following the season. Supplemental feeding is frowned upon in some circles due to its association with the spread of disease, but it is an effective way to provide a high quantity of nutrients to your deer in a short period of time. However, a more eloquent solution might be to plant forages as part of your hunting plots that donxe2x80x99t receive much pressure during the breeding season. Brassicas often donxe2x80x99t receive much browsing pressure until late in the hunting season (or sometimes after) because their palatability is influenced by cold temperatures. Theyxe2x80x99re often ignored by deer during the hunting season, and become sought after during later months, when your bucks could use that extra kick.
7. Finally, you can manage your deer herd in such a manner that you take some pressure off the bucks. The breeding period might extend for three to four weeks, which is a long time for bucks to sustain the effort that they expend. In the South, the breeding period tends to be even longer and bucks are challenged even more.
If you balance your sex ratio and increase the proportion of mature males in the herd, youxe2x80x99ll find that your breeding season will become shorter (see the November 2018 issue) and the rutting behavior more intense. This means that the bucks do not need to sustain their effort for as long a period and will exit the breeding season in better condition. This could positively influence your herd and improve post rut survival of your bucks.
More importantly, youxe2x80x99ll likely improve the survival of that big one that you passed up this year in the hopes of seeing him next year.
xe2x80x94 Dr. Steve Ditchkoff is a professor at the School of Forestry and Wildlife Sciences, Auburn University. He manages the deer research program at Auburn and has been conducting research on white-tailed deer for 25 years. Much of this research is conducted in a 430-acre enclosure, a unique research environment where researchers have the ability to gain intimate, lifetime knowledge of each individul deer while also maintaining xe2x80x9cnaturalxe2x80x9d behavior as much as possible.
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Literature Cited
Ditchkoff, S.S., E.R. Welch, Jr., R.L. Lochmiller, R.E. Masters and W.R. Starry. 2001. xe2x80x9cAge-specific Causes of Mortality Among Male White-tailed Deer Support Mate Competition Theory.xe2x80x9d Journal of Wildlife Management 65:552-559.
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