Unraveling The Mysteries of the Sun and Moon

These numbers might discourage some. Others may find hope in them. Whatever your view, they’re true nonetheless. We might as well know it up front and accept it. That way, we can turn it to our advantage, or if necessary, plan around it as best we can. What numbers am I speaking of? Of the 500-plus mature bucks harvested during my 20-years with Georgia’s Burnt Pine Plantation, 75 percent of them were taken during the two-week period between November 1 and 14, even though this two weeks only represented 29 percent of the seven-week season and pressure was fairly evenly spread throughout the season. Furthermore, almost 50 percent of them were taken during the week spanning November 3 and 9, which only represented 14 percent of the total season! 

What gives? The rut! You can shake it up anyway you like, but this one fact remains – the rut is the best time to shoot a trophy whitetail. Mature bucks are so much more vulnerable during this time that we at Burnt Pine viewed their rather sudden appearance in the harvest as the best indicator of when the rut was underway.

In Middle Georgia, the annual rutting ritual normally hits full swing the first two weeks of November. Over the years, we grew to expect the peak of rut to kickoff around November 3 and for hot action to continue for about a week before tailing off. Some years, the pattern held better than during others. Occasionally, we would see the timing of the hottest rutting activity shift a bit either way. Once in a while, classic rutting activity would crank off the last of October. Other years might have seen the rutting ritual start slower and extend later than usual, perhaps almost to Thanksgiving. More often than not, these shifts from traditional peak-rut dates seemed to be accompanied by an unwelcome side effect – a less intense, more spread-out rut. But over the long haul, the timing and nature of the rut were basically variations off a dependable central theme. Yet, for the serious trophy hunter, being able to predict both the timing of the central theme and when variations off that central theme are likely to take place are crucial to consistent success. 

I need to warn you that we’re not dealing in absolutes here. We’re not going to be able to cram the whitetail rut into a perfect little box. The animal is too complex for that. Besides, this is not a one-factor-controls-all kind of thing. Many factors come into play, some innate, some environmental and some circumstantial. Still, we can come up with some practical parameters and a solid understanding of the major players in rut timing that will serve you well when trying to time your hunt to correspond with the rut or develop an overall fall strategy. 

The Overall Concept

I’m going to start by getting the cart ahead of the horse. Right up front, I want to lay out the general concept in the simplest way I can. I feel this is necessary in order to set the proper context for what is to follow … and because what is coming can get a little complicated. But first, a qualification.

When talking about the rut, there are really two different aspects – the ritual activity associated with the rut and breeding per se. We hunters are more interested in the ritual activity, i.e., the deer movement associated with traveling, scraping, rubbing, chasing, trailing, etc., than in the breeding. True, the two normally go hand-in-hand but not always. It is possible for breeding to be underway with little accompanying ritual activity, and vice versa. Unless otherwise noted, most of our discussion will be directed toward ritual activity.

Here’s the concept – the timing of the whitetail rut centers around a narrow “ideal” window of time corresponding to specific calendar dates. However, the full moon nearest to the ideal breeding window and certain herd and environmental conditions can, within certain “allowable” limits, cause shifts in the timing and intensity of rutting activity, and perhaps even breeding.

In this series, I’ll try to explain what lies behind this concept, identify the major players in rut timing and try to put it all into a context you can take to the field.

Basic Breeding Biology

We’ll start with some basic whitetail breeding biology. We’ll go first to the root of the thing that controls the timing of the rut. Nothing about this whole process is random. In fact, the very survival of the species lies behind the timing of the rut. I’m talking about reproduction. More directly, the controlling factor in rut timing is fawn survival. You see, the timing of the rut is actually dictated by what happens about 200 days after breeding, when the fawns are born. 

Nature has selected a breeding time that results in a fawn drop when conditions are best for maximum survival. That optimum window is narrower in some places than in others. In regions with harsh weather, such as the northern Canada, or frequent natural calamities, like floods in the Mississippi River Delta, the window is quite narrow. Fawns born there outside the best time have a greatly diminished chance of seeing their first birthday. In mild regions largely devoid of extremes in weather or natural disruptions, like much of the South and East, the time of best survival is wider, but still limited. Cover, food availability, drought, floods, rain, snow and cold are all factors that can constrict the fawning window. 

Given all this, environmental pressures have dictated a preferred window of time for fawning. Certainly, not all fawns are born during this time – nature doesn’t bet it all on one toss of the dice – but the majority are. Though the preferred fawning window may be as long as two, three or even four weeks, the heart of that window, the ideal “centerpoint,” is shorter. For our purposes, we’ll call it a week. Moving forward roughly 200 days will give us a corresponding ideal window for breeding. This is the time around which the deer herd “wants” to center its breeding. In this discussion, the ideal centerpoint window for breeding will be synonymous with the “traditional peak of rut.” We’ll reference the traditional peak week throughout this chapter, not because there’s any particular magic in a one-week designation but because it allows us to talk about the heart of the rutting window in specific terms. 

The question arises: What signals the approach of this ideal time and marks its arrival? In short, how do the deer know it’s time? It has to be something that doesn’t change from year to year. It must be timed to the seasons since the climatic conditions affecting the fawning window are related to the seasons. It can’t be weather since that varies from year to year. It can’t be temporal environmental factors because they, too, change. It can’t be the moon, at least not acting alone. After all, the moon repeats its cycle 12-plus times a year, making it a less-than-ideal annual trigger. Plus, when the various moon phases occur changes from month to month and year to year (phases do not correspond with calendar dates), making moon phases an unlikely candidate to be the trigger for precise rut timing. So, what signals the timing of whitetail breeding? 

Daylength is The Key

The thing that signals breeding startup is the same overriding factor that triggers all the other changes – coat changes, antler growth, velvet-shedding, antler-casting, hormonal changes, etc. – whitetails undergo throughout the year. I’m talking about the amount of light and darkness in a 24-hour period. We’ll just call it daylength. It is the constant that cues, among a multitude of other things, the most important act in the whitetail’s existence – propagation. Though daylength is constantly changing throughout the year, those changes are constant, predictable and tied directly to the seasons and a date on the calendar. This is an important point: a specific date on the calendar equates to a specific daylength in the continuing cycle of shortening and lengthening daylength. Plus, daylength is directly related to the seasons; in fact, daylength determines the seasons. The beginning of each season is marked by a milestone daylength occurring within roughly one day of the same date each year. No other influence is as constant as daylength or as important in controlling the whitetail cycle. This bears closer scrutiny. 

Daylength And Our Calendar

Our calendar is based on the 365 days it takes the earth to make one revolution around the sun. (We’re going to ignore the additional fraction of a day it takes to make a complete revolution that leads to a leap-year adjustment every four years.) During this trip around the sun, the earth remains in a constant 23.5-degree tilt to the sun. As a result of the earth’s changing position in a revolution around the sun, the latitude at which the perpendicular rays of the sun strike the earth constantly and predictably changes on a north/south bases. Therefore, the northern half of the earth receives more sunlight when the axis is tipped toward the sun and less as the axis tips southward. The constantly changing angle of the earth’s axis to the perpendicular rays of the sun results in our seasons and a pattern of consistently changing daylengths. This allows us to divide the year into days (dates) that represent specific daylengths and into natural periods we call seasons, which are each characterized by certain weather patterns. As a result, our calendar not only allows us to mark time based on a natural cycle (one trip around the sun), but it also means that a certain date on the calendar stands for a certain night and daylength, tying calendar dates directly to daylength and cyclic whitetail deer behavior. 

Let’s complete the picture by relating all this to the four seasons in the Northern Hemisphere. The vertical rays of the sun reach their northernmost point on the earth’s surface on June 21. This day, called the summer solstice, marks the beginning of summer and is the longest day (most hours of sunlight) of the year. At the other end of the spectrum, the winter solstice, when the vertical rays of the sun strike the earth at their southernmost point, occurs on December 22. This, the shortest (darkest) day of the year, begins our winter and is followed by progressively longer days until June 21. The sun is perpendicular to the equator twice a year in its north/south movement across the earth’s surface. Both times mark the beginning of a season. The spring equinox occurs on March 21 and ushers in spring. The autumnal equinox marks the beginning of fall on September 22. In the whitetail’s light-controlled reproductive cycle, the ever-shorter days following June 21 and continuing until December 22 bring specific and predictable biological responses.

Over the centuries, deer in a given locale have developed an “internal clock” that initiates the breeding process at certain daylengths. That preferred daylength might be called the “macro-timer” for whitetail breeding. All evidence points toward this macro-timer being genetically ingrained in deer at a given locale, having been arrived at over time by the fawn survival requirements of the herd. Each herd is genetically predisposed to respond to changing daylengths at particular times in the annual cycle. Rutting time can be as early as August and September, which is true of South Florida, or as late as January and February, as is the case in parts of Mississippi and Alabama. 

The Moon – The “Lesser” Light 

So, we find that the amount of light is a trigger in the timing of the reproductive cycle of the whitetail. However, daylight is not the only light source that figures into the equation. Moonlight also is a player in timing the rut. Think of it this way: Daylength controls the preferred window and ideal centerpoint for whitetail breeding, but moonlight, especially the full moon, can cause minor shifts in the exact timing and intensity of the rut within the preferred window. Before we get into the mechanics of the moon’s effect, let’s briefly see how the moon cycle and phases work.

Moon Cycle and Phases

The moon orbits the earth in a consistent, predictable pattern. Thus, moon phases repeat themselves at predictable intervals, every 29.5 days to be precise. The months (“month” has its origin in the word “moon”) of our calendar roughly correspond to the time it takes for the moon phases to repeat a full cycle … but not exactly. That’s because our 12 months are set up to equal a calendar year (the time it takes the earth to rotate around the sun), which is actually about 12.4 moon cycles. Thus, moon phases are out of synch with our months and year. The end result is that moon phases don’t line up with specific calendar dates or daylengths, meaning that the peak breeding window could fall on any moon phase in a given year. 

The four main moon phases – new moon, first quarter, full moon and third quarter – are identified primarily by how much of the moon’s lighted surface is visible. Of course, moonlight is simply reflected sunlight, the visible amount depending on the moon’s position relative to the earth and the sun as it rotates around the earth during its 29.5-day voyage. It’s reasonable to think of each phase as lasting seven days, the actual day of the phase and the three days before and after. Since moonlight (or the lack thereof) is the thing we believe to be a player in breeding activity, then logically the new and the full moons are the most likely suspects in the equation. (True, the moon’s effect transcends mere light. Certainly, the gravitational pull of the moon has a very dramatic impact on the earth, especially ocean tides. Though I have seen for myself the effects moon-caused tides have on fish, I’ve never been able to carryover that effect to deer in a measurable way. I’ll leave that argument for another day.) Let’s take a look briefly at each moon phase. 

The new, or dark, moon occurs when the moon is positioned between the earth and sun. Thus, from earth, we view the shadowed backside on the moon during daytime. The new moon essentially rises at sunrise and sets at sunset, offering practically no reflected light at night. As the moon moves away from the sun to a more perpendicular angle to the earth, more and more of the lighted side of the moon is visible with each passing day. (Increasing moonlight is calling waxing; decreasing waning.) About seven days after the new moon, we arrive at the first quarter, when half of the moon is lighted and visible. The first-quarter moon rises about noon, hangs overhead at dusk and sets about midnight, providing light only during the first half of the night. 

When the moon moves all the way around to the far side of the earth relative to the sun a week or so after the first quarter, we get a full view of its lighted surface from about sunset to sunrise. This is the full moon. It sheds light on the earth throughout the night and reaches meridian (its highest point) about midnight. After the full moon, nighttime light diminishes as the waning moon moves back toward the sun. The half-illuminated third quarter arrives about seven days later. This phase rises above the horizon around midnight and sets around noon, emitting light only during the second half of the night. It is at its highest point at sunrise. An easy way to remember when the four phases shed their light at night is: new moon, no light; first quarter, first half; full moon, all night; third (last) quarter, last half.  

Summing It All up

So, we come to this: While calendar dates are related to specific daylengths that are essentially constant from year to year, moon phases do not occur on the same date from year to year, and thus are not tied to specific daylengths. The fact is that a given moon phase can fall as much as two week either side of any fixed date. Worse yet, if you’re trying to key off a specific moon, such as the Harvest Moon (which is the full moon hitting nearest September 22), then over the years, it is possible to have swings of up to 30 days in when that particular moon hits. That is too much variance in the timing of the whitetail rut and presents real problems with using the moon as a primary timer of something with the precise breeding requirements of the whitetail. The moon is just too much of a wild card in nature’s scheme to be the overriding timing cue for the rut.

Does that mean the moon has no impact on the timing of whitetail breeding? No, it does not mean that. It simply means that whatever role the moon has is second fiddle to the more important constant – daylength. Yet, since the timing of whitetail breeding is light-controlled, moon phases, particularly the brightest moon (full) and the darkest moon (new), introduce another light variable that I believe does have an impact on whitetail breeding. Next month, we’ll explore exactly what role the moon has in the timing of the all-important rut.

(Editor’s note: This article was excerpted from David Morris’ new book, Advanced Strategies for Trophy Whitetails.”)

Now, you may ask what about deer from one region stocked into another region with distinctly different rut timing? For a while, the relocated deer’s genetic programming will continue to dictate a rut timing consistent with that of their place of origin. However, over time, the rut will gradually shift toward the ideal breeding window for that locale because of environmental pressures on fawn survival. Often, restocking takes place where native deer already exist to some degree. Interbreeding between the introduced deer and the local stock hastens the move toward the ideal rut timing for that locale. Normally, after a few generations, the herd settles into a rutting schedule most suitable for maximum fawn survival. The speed at which that happens is determined by the severity of the environmental pressures and the numerical relationship between introduced deer and local deer.