“Try as we have to disprove the hypothesis that the full moon triggers breeding,
we have not been able to reject it. We have disproved the hypothesis that moon
position has any real effect on activity.” Dr. James Kroll
A full moon rising on the eastern horizon reflecting light from a quickly vanishing sun provides an illuminating eeriness as its orange glow backlights a naked, statuesque November tree line. Through time, man has studied, gazed upon with curiosity, romanced, fantasized and even set his foot down on the surface of this terrestrial sphere. When hung in an autumn sky, the moon’s looming presence enchants us and casts a spell of mystique upon the deer hunter.
What influence, if any, does the moon have on white-tailed deer activity, particularly their breeding cycle? Does the moon hold the key to unlocking the mystery of why 70-80% of whitetails breed on different dates each November? Following an exhaustive multi year study here in the Northeast where I meticulously monitored both autumn deer activity and spring fawn births coupled with the collected data from what became an almost 20-year research project conducted by the late wildlife photographer, Charles J. Alsheimer and former Vermont Game Commissioner, Wayne Laroche, I’m convinced that the moon certainly does indeed play a huge role in triggering the rut. In fact, according to Laroche,
If the moon provides the timing mechanism for the estrous cycle, what sensory pathway in deer receives the lunar cue? External stimuli fall into three primary categories: physical, chemical, and biological. The great distance between earth and the moon rules out any regular 28-day exchange of sounds, scents or chemical and biological materials whitetails can detect.
The moon affects the earth’s gravitational fluctuations and nighttime illumination. Both factors create external stimuli that deer might detect. However, little evidence suggests deer or other creatures directly detect gravitational forces.
Moonlight can be detected, especially by whitetails, which have eyes adapted for low-light vision. Light passing into the eye strikes the nerve-rich area in the back of the eye, causing electrical impulses to pass along the nervous system to various organs. Some impulses pass to the pineal gland in the center of the brain, and provide input to the endocrine system. The pineal gland and related hormones are involved in or regulate the reproductive cycle. The pineal gland responds to light by increasing (with diminishing light) or decreasing (with increasing light) production of a hormone called melatonin. This, in turn, increases or decreases other hormones.
The fact moonlight changes the earth’s illumination on a cycle similar to the whitetail’s 28-day estrous cycle, the fact whitetails have a sensory system that can detect moonlight, and the fact the whitetail’s endocrine system responds to light stimuli by altering levels of reproductive hormones argue against coincidence.
The Autumn Dance
Alsheimer, Laroche and I believe that the 14-day breeding window, the time frame when 70-80% of the adult does will enter estrus, begins five-to-seven days after the second full moon (rutting moon) following the autumnal equinox (Sept. 23). This scenario holds true the closer to November 1 the rutting moon falls, intensifying the rut and facilitating a more predictable breeding timetable. The light of the full moon is the visual cue that stimulates the bucks and as it waxes over the next 5 days, the darkening nights become the impetus to trigger the doe to begin ovulating.
On the other hand, in years when the second full moon after September 23rd falls on or later than November 14th, the less intense the rut will be. This is commonly referred to as a trickle rut. Breeding will begin on the full moon when this scenario presents itself.
Due to the three overlapping stages involved in this forty-day process, bucks will exhibit distinct behavioral changes and as the rut develops it becomes equivalent to a marathon rather than a sprint. To better define the commonly used word, “rut,” I’m refering to the actual breeding period and the events leading up to it.
Seeking: This sudden transformation in the buck’s chemistry urges him onto his feet in search of does. Bucks will begin seeking about a week prior to the full rutting moon. As the reflective light becomes full, a buck’s search becomes accelerated and his travels now take him far and wide of his normal home territory. The animal’s nose dictates the direction of his travel. Rubbing and scraping intensifies and with each doe encountered, the buck will test her urine by ingesting the scent through the vomeronasal organ located in the roof of his mouth. This behavior, flehmening, routinely called lip curling, discloses immediately to the buck if the doe is approaching estrus.
Chase: During the process of seeking, a buck will finally pinpoint a doe near estrus. In his frantic search to locate and be the initial suitor, he will chase every doe encountered. This activity usually begins a couple of days following the full moon. Frustration mounts within the buck fraternity, as trees, shrubs, ground cover, and even each other become the recipients of brutal attacks.
Tending: Five to seven days following the full moon does will enter into estrus. When this event begins, all other rut related activity such as scraping and rubbing ceases with the buck’s full attention riveted on the act of breeding. This phase will encompass fourteen days peaking at the halfway point. 70-80% of mature does will be bred during this period.
Suppressant variables
Several influences can and will suppress deer activity during daylight hours. Weather and temperature are two of the biggest contributors that can make or break a frenzied rut. If an extended period of rain or snow is predominant, breeding activity might occur earlier as dense clouds shorten day length or it can be delayed due to the deer’s reluctance to move under such adverse conditions. When the temperature rises above 45 degrees, whitetail activity shuts down. The deer will continue to breed, only now it will transpire entirely under the cloak of darkness when it’s much cooler.
Another factor attributed to curtailed deer activity during daylight is human pressure. If hunter densities become increased, whitetails are quick to respond by diverting their movements to nighttime. Or, if the buck-to-doe ratio becomes greater than 3 does for every antlered buck, competition amongst rivals is significantly diminished thus negating the bucks need to search for available does.
Although these influences can hinder the huntsman on his quest for venison, the sign being left by the resident whitetails proves conclusively that rutting behavior is indeed taking place.
Natures Timing is Precise
The well-orchestrated autumn rutting events, while they play a key role, are all pieces necessary to complete the procreation puzzle for whitetail deer. Remember, it is the female that dictates when breeding occurs. The doe involuntarily takes her cue from diminished light, both sun and moon, activating her endocrine system which releases reproductive chemicals cycling the doe into estrus.
With 70-80 percent of the does conceiving during the fourteen day breeding window, approximately five to seven days following the rutting moon, their fawns will arrive during the fourteen darkest nights of the spring moon. Moon breeding is timed as a natural selection mechanism to ensure survival. What about the does that conceived early and those that didn’t take the first time? The moon and the whitetail’s estrus cycle are both on a 28-day period. Therefore, for those does impregnated in October, their fawns will still be born on the dark side of the moon, only earlier. The same holds true for the December conception with the fawns dropping a month later, yet still under a darkened moon phase. Birthing on the dark side of the moon provides the fawn a brief advantage from predation while in its cryptic stage.
The Significance for The Hunter
It would seem that if we were armed with the knowledge beforehand as to when buck activity will be at its greatest, our decision making process would become more precise. Hunting weeks could be selected well in advance, locations to hunt within a certain parcel are now picked based upon perceived deer behavior, and different methodologies can be instituted to compensate for the phase these animals are currently in. This cranial ammunition certainly won’t guarantee you a buck, but it goes a long way psychologically in preparing and enacting precise decisions during the hunt.
2020 Breeding Dates
With the second full moon appearing on October 31st , this year’s breeding season should be intense. I expect to see increased buck activity a few days prior to Halloween. By the time the full moon appears the chase will be on and continue in earnest through the entire first week of November. November 5th will find the first does coming into heat, ready to breed. Find these girls and all the boys of the neighborhood won’t be far away.
Veterans day, which falls on a Wednesday this year will serve as the day when numerous does become ready to breed. This process will get played out for approximately the next 10 days. On November 20-to-22, bucks will begin entering the final phase known as the recovery period, a 5-to-7 day time when the male will ultimately crash from physical exhaustion. They will retreat back to their sanctuary where they will spend up to 75% of the time bedded in an effort to recuperate. If I can offer any advice for this year, it is to find the girls!
Conclusion
Although nothing is foolproof when it comes to whitetails, there has been far too much evidence pointing me towards the beliefs I now hold for the whitetails all-important breeding season. I’m quite sure there will be more pieces added to an already complex puzzle as the years unfold, but that’s what keeps my interest alive as I thirst to try and understand this fascinating animal. In the process, hunters such as yourself become the beneficiary of what is brought back from my wanderings amongst the white-tailed deer, and that my friends is from where my ultimate gratification comes.
All images and text on this site are copyright protected and the property of R.G. Bernier
© 2020 R.G. Bernier Nature Photography – All rights reserved.
bigwhitetail 
Posted on October 13, 2020
0