NAW Debate: Why the Rut Ain't What it Used to Be
October 29, 2013
Unless you've been on deployment in the Middle East or on an Antarctic expedition for the last few years, you've probably noticed the whitetail rut has become a bit "strange."
Throughout my roughly 45-year career as a biologist, I've seen it's common for folks to complain about hunting conditions. But recently, the complaints have been piling up at an alarming rate. There's a lot of confusion and concern about what's going on with the whitetail rut, and understandably so.
In light of what seems to be a "new normal," I think it's time we take a closer look at how things are these days, and why. My goal is to help you understand and deal with deer breeding behaviors that deviate significantly from normal, so you can be prepared for whatever scenario you end up facing in your own woods.
Consult a dictionary, and you'll see "normal" defined as something along the lines of "conforming to a standard; usual, typical or expected." For biologists, though, "normal" has a somewhat different meaning. We see "normal" occurrences as a distribution of a biological phenomenon, expressed as a bell-shaped curve. The peak of this curve represents the "average," with decreasing frequency of occurrence to the right and left of the peak. The farther you move from the peak of the curve, the less likely the phenomenon is to be observed.
For example, if we could capture all mature whitetail bucks in the U.S. and graph their gross antler scores in 10-inch categories, we'd see that the average would be about 130 inches. Of course, deer would be scattered all up and down the graph, but the majority would score pretty close to 130. Way to the left of average we'd find a very few bucks scoring a meager 50 inches...while far to the right would be the kind of giants you read features on in this magazine.
We've learned over the years that it's possible to shift the average score, moving the peak of the curve toward one of its tails. Whitetail management in the last two decades has tended to move the curve to the right on well-managed properties. Unfortunately, excessive hunting pressure on bucks in some poorly managed areas has shifted the curve to the left.
It's really no different when discussing the biological events associated with whitetail breeding. There's an "average" date for when does in a given population are bred, and most mating occurs around that time. But there also are cases well to both sides of the peak. And the more stressed and/or imbalanced the herd is, the more elongated the rut curve is.
Nature intends for whitetails to have a concise rut, with its timing set to offer the best odds of adequate fawn survival. As we'll discuss, that timing is the result of genetic selection. But in recent years, factors other than genetics have had profound influences on the rut. One of those is population density; the other is climate.
Relative to the "good old days," whitetail populations have increased in virtually every part of North America. Indeed, they've reached or exceeded the habitat's saturation point in most. Even relatively "new" whitetail areas in Iowa and Oklahoma now are having some issues as a result of high deer numbers. While they might still be solid overall hunting locations for big bucks, they aren't necessarily as great as they were at their peak of productivity.
What does this mean to whitetail reproduction? The No. 1 limiting factor to almost everything a deer does is nutrition. Lower nutritional quality affects normal breeding biology. Deer on a poor diet, even seasonally, might not breed when they're genetically programmed to do so. Whitetails instinctively prepare for the rut in a linear, structured manner. First, as fall approaches, they have to change from a summer to a winter coat. Does also have to regain reserves lost due to nursing. Bucks must build up muscle, mineralize antlers and begin what equates to an Olympian's training program as they prepare for the rigors of the rut.
When there's inadequate nutrition, these steps don't occur at the proper times. And the impact is particularly important on does. For instance, going into fall, within a group of does you might find some individuals still with their summer coats and others already in winter coats. The latter are in better condition, usually because they've lost their fawns and thus haven't been held back by the need to continue producing milk.
This variance within a doe group translates to asynchronous estrus cycles, with some coming into heat much earlier than others. And this of course extends the breeding period out over many weeks instead of days, as once was "normal" with a smaller population of healthier animals.
It's hard to argue with anyone who claims the climate has changed over the last 50 years. I, for one, think the changes are just part of "normal" swings in climate that have taken place hundreds, thousands or even millions of times. But for purposes of this discussion, it doesn't matter if man-caused "global warming" is real or not — overall, it's hotter and drier in a lot of places than it used to be.
Drought and heat have significant impacts on deer behavior and physiology. Drought obviously affects the quality and quantity of deer foods produced, and in some cases even the animals' ability to consume enough water. Heat affects deer movements and their interest in feeding. Put the two together and you have major stress.
A third factor in this comes under the heading of "celestial events." If you review the dates of full moons closest to the normal peak of whitetail breeding over the last few years, the results are fascinating.
There are two camps of biologists when it comes to the moon's effect on breeding. Our research long ago substantiated that the species "wants" to breed within 3-5 days after the appropriate full moon. Does and bucks alike prime on the sequence of lunar cycles as fall approaches.
However, not all subspecies prime on the same full moon. For example, whitetails in the Midwest prime on the one in November, while those in South Texas prime on the one in December. Again, the timing of breeding varies from place to place in order to maximize fawn survival. Once weaned, a fawn is on its own nutritionally; if during that time there's abundant, highly digestible forage, it's more likely to survive.
For every subspecies the gestation period is about 198 days, and weaning occurs 45-60 days after birth. In South Texas, rainfall historically peaks in early fall, often coinciding with hurricane season. The rains seldom cause significant flooding of deer habitat but greatly improve forage conditions in this semi-arid region. So if a doe can get her newborn fawns through the heat South Texas endures in mid-summer, by the time they're weaned, the forage conditions will tend to be adequate for them. This wouldn't be the case if they were dropped in late spring, as is the case in most other regions.
Of course, threats to fawn survival can take many forms. In Michigan, a fawn must be conceived by around the middle of November to have a good chance of making it through its first winter. Meanwhile, in the Mississippi Delta, a fawn conceived in mid-November would be born during what's historically the flooding season. That flooding can be extreme and a direct threat to survival of young deer. So most breeding occurs much later there.
Of course, the full moon in any calendar month shifts dates from year to year. Deer have a built-in timing mechanism that compensates for years in which the full moon happens to occur too far from the "preferred" time to breed, but there's a limit to the flexibility. It's much like an elastic band that can stretch only so far before it breaks. So when the full moon falls too far outside the norm, the rut seems to be off.
Another significant variable is that many whitetails now live in areas far different from those in which their ancestors did. This is largely a result of years of restocking efforts during the 20th century. After the native deer adapted to a given area were wiped out by forest clearing, overhunting and the like, they were replaced by whitetails from random sources. Sometimes these "stockers" had evolved 1,000 miles or more from where they were dumped. And sometimes deer from yet another area were released there as well.
This naturally created havoc for the rut. Imagine crossing the Gulf Coast's Avery Island subspecies, which has a peak rut averaging in late September, with the South Texas strain, which has a peak rut in December. That's exactly what happened in many areas of Texas, which got whitetails from both regions. The result is a hodgepodge of breeding dates.
The new norm is a trend toward "trickle" ruts: those in which does come into estrus over an extended span of time. Those in good physical condition breed first, followed by others as they recover physically. What this means is that in years with adequate, well-timed rainfall, the rut is more concise and timely, while in drier or otherwise more stressful years it's more spread out.
Drought and excessive heat tend to go hand in hand. And because average temperature also affects movement, deer often become even more nocturnal under droughty conditions. Running around in a fur coat in high daytime temperatures is not their cup of tea. Common sense suggests they need to need to spend more time looking for food when it's dry, but the heat tends to suppress daytime movement.
Agriculture obviously is impacted by climate as well, and this can affect deer in unpredictable ways. For example, last year's drought in the Midwest's corn-soybean belt caused significant crop failures. We might assume this would have caused deer to be in poor condition. However, while farmers abandoned the fields as lost, most still produced some beans or corn.
I observed many fields with stunted plants, each with only a few seeds attached. These crop seeds were highly attractive to deer — and with no farmer harvest, they remained available to wildlife deeper into the fall than usual. This changed the dynamics of hunting season dramatically. The bottom line is this: In many locations, rut hunting has changed. So what can we do about it?
Adapting to the Rut's New Realities
The longer you hunt an area and observe its deer herd, the better chance you have of staying a step ahead of what the animals are doing. This is especially true when nature throws you a curve ball during the rut.
Patterning deer is a concept that continues to confuse many hunters. However, understanding its basic elements is critical to making sound hunting decisions. And that starts with being clear on what patterning really is.
In our 1994 book, The Art & Science of Patterning Whitetails, Gordon Whittington and I started out by explaining what patterning is not. We aren't trying to figure out which oak a specific buck is going to walk past at a specific time next Tuesday. Sure, we'd love to know that before next Tuesday gets here, but that isn't the real point of patterning. To us, patterning involves learning as much as you can about the overall deer population in a given hunting territory. That includes not just the timing of their rut but also food source dynamics, general travel patterns and the locations of preferred bedding areas and sanctuaries.
Of course, for patterning to help any of us make good hunting decisions — during the rut or any other time of season — we also must be able to take this knowledge and predict what deer will do in response to various environmental changes. This is largely a matter of experience and skill. To consistently harvest older bucks takes work and attention to detail. But, hey, that's the fun of deer hunting!
The first step in preparing your rut strategy is determining when your deer "want" to breed. Fortunately, many sources of information now are available from university deer scientists and wildlife agencies. If possible, get multi-year data for your area and benefit from what those numbers have to say.
For instance, let's examine the accompanying graph of breeding data from four years in the northern Lower Peninsula of Michigan. The yellow box indicates five days to each side of the rifle opener, which is always Nov. 15. As you can tell, this basically guarantees the opener will miss the peak rut. But there was considerable year-to-year variation. Just within a 4-year period (2005-8), in that region the rut curve moved as much as 14-15 days!
Another factor in play is moon phase. Take, for instance, the dates of full moons for the late summer-early fall period since 1990. If we compare the full moon dates for each year since then, 2012 stands out from the other years. Thus, it probably played a role in the strange timing of the rut last year.
There are two things worth noting with regard to the full moon dates in 2012. First, month-to-month variation in full moon dates was very low. In 2012, five consecutive months had "late" full moons. In fact, there was a "blue" moon (second full moon within a calendar month) in August. If you know when deer in your area typically breed, checking the upcoming calendar and plotting moon phases for around that time might give you some idea what will happen this season.
Note I used the word "might." I do so because there are other factors to consider here. One of them is precipitation. Remember, in 2011-12 large parts of North America experienced extreme drought conditions. For instance, Texas recorded a "millennial" drought, meaning it had the severity expected only once in 1,000 years. And much of the Great Plains saw extreme drought in 2012.
In my view, the reason some scientists don't believe as I do about full moons and their effect on whitetail breeding is they've been studying abnormal, habitat-saturated deer herds most of their careers. Those have become the new normal!
Hunters spent most of the 20th century dramatically altering the population dynamics of whitetails through so-called traditional deer management (TDM), in which the heaviest harvest pressure is exerted on bucks. This mentality unfortunately lingers in many places. The result is high deer numbers with skewed sex and age ratios.
TDM has led to an increasing occurrence of trickle ruts. In some cases, does have to cycle 2-3 times before being bred. Add in the impact of changing climatic conditions, affecting both food availability and deer movement, and the stage is set for more difficulty finding a mature buck to shoot. Again, dealing with these factors involves learning to pattern your deer population.
You need to know availability and quality of their food supply in summer and early fall, as this will help you predict the herd's physical condition as the rut approaches, You also need to know where and how deer travel about your hunting area under different weather scenarios. And finally, you need to be able to recognize cues correlated to the timing and intensity of the rut. Let's have a look at each of these.
An important aspect of patterning involves keeping track of food sources over the year. The field so lush last year might be fallow this year. The acorns you often depend on to find your buck could be all but non-existent, whether due to an unusually late freeze or summer drought. You must keep track of what's going on and use it in plotting a strategy.
I try to keep maps and aerial photos of every place I hunt, and I monitor what's happening month to month within the deer landscape. Even in very droughty years, there's always a place where the soil is a bit wetter. You generally can find a few acorn-bearing oaks that were sheltered by a warm hillside during that late frost, when the rest of the trees lost their crop. Find the food and you'll find the does. Find the does and you'll find rutting bucks.
Since the development of trail cameras, they've become an essential tool for most serious hunters and deer managers. I try to run cameras all year, watching what's happening physically with the deer. And even before breeding starts, this can yield helpful rut info.
For instance, let's say you've been getting photos of the same four does, and it's clear only one has a fawn. Some are transitioning to winter coats early; others have worn-out reddish summer coats. You know right away the rut won't fall within a tight window. The does with early winter coats will be the first to come into estrus, so keep track of them for signs the action is about to start.
Mapping rub lines has been a critical component of patterning deer for most of my career. Bucks are more than happy to tell you where they travel by leaving strings of damaged/ dead saplings. Keeping records and developing maps on where these are will greatly aid in dealing with the changing dynamics of the rut.
If you hunt the same place every year, keep track of the time rubs are first worked and when rubs in specific areas go dormant, as well as scrapes. Then try to correlate this activity with weather and moon conditions. Ask yourself: "In dry years, do my bucks tend to relocate early activity to specific areas?"
Lastly, paying attention to the sex and demographics of deer observed in the area can be one of the most important factors in patterning them. In herds with decent buck age structure, early in the pre-rut you see mostly young bucks (ages 1 1/2 or 2 1/2). The older bucks tend to be heavily nocturnal. As the rut approaches, however, young bucks tend to disappear and become nocturnal as well. The older bucks then move about at all hours. Their increased activity can limit the visibility of younger bucks.
As does come into estrus, a mature buck will find one and give chase. The sounds of the chase will attract bucks of all ages. As the chase plays out, however, odds are that the more dominant bucks in the vicinity will be around her, with young and overly mature bucks (if present in the herd) bringing up the rear.
If during your summer camera census you see only young bucks, you can be sure there are few mature bucks on the property at that time. You at least should be able to photograph older bucks at night. So if you see none, that's a bad sign. Now you're left to hope one simply wanders into the area during the rut.
You also can use trail cameras to estimate an area's buck:doe ratio. Simply add up all photos of does and bucks (no matter how many times you photograph the same buck), then divide the number of individual doe photos by those of bucks. If this estimate doesn't show at least 1 buck per 2 or 3 does, you'll have some difficulties ahead! Move to another area, if possible, to find tighter sex ratios and a more intense rut. Meanwhile, increase doe harvest on the unbalanced herd.
The past several decades have seen tremendous whitetail population growth, and today there are few places where herds still are growing. At the same time, climatic conditions and habitat quality have worsened. In some areas, agricultural activities also are declining. As a result, we deer hunters must learn to cope with a "new normal." Only those who do their homework will be consistently rewarded.