Just how much does the moon influence deer movement and rut activity?
It was 4 p.m. - broad daylight - when I glanced out the window and saw five deer strolling up the back field. Seeing deer in the back yard isn’t all that unusual, but they typically don’t show until the last half hour of daylight. Furthermore, all five deer seemed rather nonchalant as they paraded up the middle of the open field directly toward the house. It was as if they weren’t even aware of their surroundings - until I opened the window to snap a few pictures. Then they all looked up and reacted like they’d just woken from a sleepwalk, bolting back to the concealment of the adjacent woodlot.
“Odd,” I thought, raising an eyebrow. As I did, I glanced a possible explanation. The moon was already up overhead, and nearly full. Was that the reason for the deer’s odd behavior? Or was it merely coincidence?
How - or even if - the moon influences deer behavior is one of whitetail hunting’s greatest unsolved mysteries. Many, from pure recreationists to trained scientists, have tried to prove or disprove the concept. Recent years have seen a growing number of theories related to moon phase and position. Yet we still can’t say for sure.
MOON-PHASE THEORY #1
Many hunters believe the moon influences deer movement. Science has proven it influences tides, fish migrations and human behavior. It only makes sense that it would also affect deer in some way. But how?
One of the most widely accepted beliefs is that during the full moon, deer move more at night and less during the day. The explanation often given is that deer can feed all night under moonlight, where they feel more comfortable, and thus won’t need to move much during the day. That seems both reasonable and logical. But what do the scientists say?
In their book “Solving the Mystery of Deer Movements,” authors Dr. James Kroll and Ben Koerth wrote, “Because the moon is such a noticeable phenomenon in our world ... it seems almost intuitive it must have equally profound effects on the habits and lifestyles of animals as well, at least we all want to believe it to be so.” Summarizing deer activity results from a trail-camera study, they found, “The lowest amount of daytime activity occurs during the full moon, while the new moon has the greatest amount of daytime feeding.” It should be noted they looked at both bucks and does.
Table 1. Effect of moon phase on daytime deer activity (from Kroll and Koerth)
Moon Phase Percent of Activity
New Moon 33.7 %
First Quarter 26.1 %
Full Moon 19.9 %
Last Quarter 33.5 %
One of the more recent attempts to shed light on the subject is a study by Dr. Mickey Hellickson, chief wildlife biologist at the King Ranch in South Texas. At the Quality Deer Management Association’s 2006 National Convention, Hellickson presented results from his research on how various environmental factors affect deer movement.
Unlike many past studies, which were based on direct observation or intermittent radio telemetry monitoring, Hellickson’s used GPS-based transmitters and activity monitors capable of pinpointing the location, and tracking the movements, of any radio-collared deer instantly, 24 hours a day, seven days a week. He also looked exclusively at bucks, which is what most hunters are targeting.
Hellickson recorded only daytime movements (6 a.m. to 7 p.m.) from October through January over a two-year period, collecting more than 420,000 observations from 43 collared bucks. He then compared these results to full-moon and new-moon periods.
Results showed that bucks were active (grooming, feeding, walking, running) 43 percent of the time, and inactive (bedded, ruminating, standing) 57 percent of the time. No big surprise there. However, results also showed daily buck movements were about what you’d expect, peaking at 7-9 a.m. and 6-7 p.m., with a slight peak at midnight. Lowest hourly movements occurred from 5-6 a.m., 3-4 p.m. and 10-11 p.m.
More important, this pattern was relatively consistent throughout the four-month range regardless of moon phase, though overall movement increased during peak rut times. Hellickson therefore concluded: “Although the moon may influence buck movements in other ways, our data did not indicate any patterns relative to the effects of moon phase on buck movements.”
MOON-PHASE THEORY #2
Most hunters don’t have the luxury of being able to pick their days, waiting until conditions are right to drop everything at a moment’s notice and head to the field. That leaves them with essentially two options: They can hunt when time allows and make the best of existing conditions; or, they can try to hedge their bets and schedule days off for anticipated prime times like the peak of rut. That, of course, requires that you know when peak rut occurs.
For decades, both the scientific and hunting communities agreed that the rut occurred at roughly the same time each year, though that time varied substantially from one geographic location to another. Then, about 15 years ago, a couple of guys set the whitetail hunting world on its ear when they began promoting a contradicting theory.
In 1990, well-known whitetail photographer Charles J. Alsheimer teamed up with Wayne Laroche, a former fisheries biologist and now Commissioner of Vermont’s Fish and Wildlife Department, to champion a new idea. They contended that not only did timing of the rut vary considerably from year to year, but that the timing was quite predictable, and it was based on moon phase.
While the Alsheimer-Laroche investigations don’t quite meet rigid scientific standards, they have been detailed and extensive. Furthermore, the findings are based on hard science and make a lot of sense. Their data shows a strong correlation between the whitetail breeding cycle and autumn moon phases.
Science has documented that the onset of the rut, like most other physiological and behavioral changes deer experience throughout the year, is triggered by photoperiodism - the response of an animal to changes in day length (the amount of available light). We also know this to be the mechanism that triggers increased testosterone levels in bucks and estrogen levels in does, which, in turn, triggers rutting behavior. Traditional rut theory, however, considered only sunlight.
Alsheimer and Laroche’s theory factors both sunlight and moonlight into the equation. Like the sun, they argue, the moon is a source of light. And while changes in the amount of available sunlight are consistent from year to year, timing of the full moon varies. If sunlight were the only influence, the rut would occur at the same time each year. If moonlight were a factor, the rut’s timing would vary from year to year, but in a predictable way.
Interestingly, scientists’ findings differed on this. Hellickson’s data showed no correlation between the rut and the full moon. Numerous other research projects have also shown the rut’s timing varies little from year to year within the same geographic location. However, most of those studies are based on fetal deer measurements, which have a margin of error wide enough to take into account the variation in the Alsheimer-Laroche theory.
Furthermore, Kroll and Koerth’s observations seem to support Alsheimer and Laroche’s theory (see sidebar). “The hunter’s moon signals a doe’s body to initiate estrus. For Northern deer ... the rut occurs within five to seven days ... following the hunter’s moon and one cycle earlier or later for Southern deer.”
Yet another theory that came, not from scientists, but from hunters, is outdoor writer Jeff Murray’s moon- position theory. Murray proposed his theory after studying precursors like the solunar table and Vektor fish- and game-activity tables, and gathering reams of anecdotal data. The basis is that the moon’s gravitational pull is stronger when the moon is directly overhead or underfoot - strongest when overhead. This is what causes tides, and limited scientific evidence suggests it might have some influence on animal behavior (including humans).
That being the case, Murray theorized the moon’s pull must also stir deer into moving. At least one study, conducted by Steve Demarais and Bob Zaiglin in South Texas partially supports the moon-phase theory. Studying 25 radio-collared bucks over a three-year period, the researchers found that buck activity most closely paralleled a typical activity pattern: peak activity at dawn and dusk, during the first and last quarters of the moon. This, according to Murray, supports his theory because the moon is peaking (overhead or underfoot) at dawn and dusk during these moon phases.
Unfortunately, that’s about the only hard, scientific evidence supporting moon-position theory. While a good many hunters have tested it and swear by it, the scientific community has largely dismissed it. Based on their research, Kroll and Koerth, too, concluded, “Moon position does not appear to predictably affect deer activity.”
In the end, it seems we’re left with more questions than answers. The scientist in me says to follow the hard, factual evidence. On the other hand, folklore based on generations of anecdotal evidence strongly supports some consistent trends about how the moon affects deer movement and behavior. Perhaps the best advice I can offer was given to me as a young wildlife biology student by one of my professors. He said, “When what you observe in nature differs from the textbooks, nature is right”.
Editor’s note: Bob Humphrey is a certified wildlife biologist, registered Maine guide and an avid whitetail hunter.
This article was published in the July 2007 edition of Buckmasters Whitetail Magazine. Join today to have Buckmasters delivered to your home.