Do Moon Phases Affect Deer Movement?

Researcher after researcher since the 1970s has failed to document any changes in deer activity during new moons, quarter-moons and full moons. Despite that lack of scientific evidence, most deer and elk hunters staunchly defend a lunar-based belief. In fact, when possible, most build their hunting schedules upon them.

Hunters who dismiss links between the moon and deer/elk movements are a small minority. How small? When Penn State University’s College of Agricultural Science and Management surveyed hunters’ opinions on lunar impacts in 2017, only 12 percent of 1,680 respondents believed moon phases had no effect on deer. In contrast, 66 percent said moon phase had “some effect” and 22 percent said it had “significant effects” on deer.

Further, 58 percent of those 1,680 respondents agreed deer travel more at night and less during the day during full moons. More specifically, 44 percent “agreed” and 14 percent “strongly agreed.” What about the other 42 percent? Only 4 percent “strongly disagreed” and 18 percent “disagreed.” The remaining 20 percent were neutral.

Meanwhile, the Penn State researchers compiled location data from adult deer wearing GPS collars in October 2015 and October 2016 to see if their movements varied during three lunar phases: full moon (greater than 67 percent illumination); partial moon (33 percent to 67 percent illumination); and new moon (less than 33 percent illumination).

Of the review’s three findings, most hunters probably already believed two of them:

• Deer were more active at night than day during all three moon phases.
• Deer activity was greatest within two hours of sunset and sunrise during all three moon phases.
• In contrast, most hunters probably doubted the third finding:
• Deer activity neither increased nor decreased significantly during all three moon phases.

An Embarrassing Lesson
One veteran deer biologist who urges hunters to believe those findings and other GPS-based research is Dr. Grant Woods, owner/creator of Growing Deer TV and The Proving Grounds in southwestern Missouri. Woods sees no scientific links between lunar cycles and deer/elk activity – including his own early-1990s research that predicted deer activity with 72 percent accuracy.

“That was an embarrassing experience, but it was a great life lesson,” Woods said of his long-defunct “Deer Activity Index,” which was also known as the “Moon Peak Activity Index” when introduced in the September 1995 issue of Deer & Deer Hunting magazine (with yours truly as D&DH’s editor). One of our cover blurbs even declared: “Now you can plan your hunt when daytime deer activity is greatest!” Inside, readers could buy a wall chart for $8.95  that predicted daily deer activity from September 1995 through February 1996 in the United States.

Woods made those predictions based on field observations from a 14-person research team that hunted whitetails in study areas from New York to Florida. They logged 1,160 hunts from 1991 to 1994, spotted 2,815 deer, and killed 435 of them. He then compared their observations with data measuring the moon’s illumination, its distance from Earth, and its degree of declination north and south of the equator. All full moons are not created equal, obviously.

“I really thought we had it figured out,” Woods said. “I mean, 72 percent accuracy was better than anything else out there by a long shot. I even presented my findings at scientific conferences. But then we started putting GPS collars on deer, and I realized I didn’t know what I was talking about.”

Possible Link?
Even so, researchers Jeffery Sullivan and Stephen Ditchkoff at Auburn University in 2016 reported some predictability in deer activity for 38 GPS-collared adult bucks. Their results, however, indicate that predictions in some solunar charts are “misleading.” Sullivan and Ditchkoff reported:

• On days furthest from full or new moons, bucks were less likely to be active during moonrise and moonset, and more likely to be active when the moon was overhead or underfoot.
• On days nearest full or new moons, bucks were more likely to be active during moonrise and moonset; and less likely to be active when the moon was overhead or underfoot.

Despite documenting those patterns, Sullivan and Ditchkoff remain cautious, noting the bucks followed a standard pattern: “The … hours surrounding sunset appear to be when deer are most likely to be active, which is already commonly accepted.” They also noted: “Increased activity does not necessarily increase a deer’s vulnerability to harvest. While a deer may increase its activity during predicted solunar periods, it may remain in areas that are not accessible to hunters, or it may avoid permanent hunting stands, a behavior documented in studies … during the hunting season.”

Lunar-Based Sweetener?
Mark Kenyon, founder of the Wired To Hunt, MeatEater contributor and host of the “Wired to Hunt” podcast, asks nearly every hunter and hunter-biologist he interviews if they believe the moon affects deer behavior. The consensus? Biologists scoff and hunters believe.

Most hunters, however, put more stock in the moon’s position than any of its phases. “The hunters I talk to generally like a rising moon or setting moon that coincides with dawn and dusk,” Kenyon said. “If the moon rises during the final hour of daylight or sets late in the morning, they expect increased deer activity. I also follow whether the moon is directly overhead or underfoot. If either position coincides with dawn or dusk, that’s exciting, too.”

Kenyon concedes hunters offer mostly anecdotal evidence for those conclusions. Where does that leave him?

“I look at moon positions and have a hard time believing it has no impact, but I also trust biologists who can’t find significant impacts in any of it,” he said. “So I fall back on this possibility: Maybe the impacts aren’t statistically significant for a herd, but maybe they’re just significant enough to affect one buck in the herd. That’s all a hunter might need that one day.”

Kenyon considers lunar impacts the sweetener in deer hunting’s coffee. He said most serious hunters list the moon third or fourth behind wind/weather, air temperature and barometric pressure. But when those factors align correctly, and the moon’s position and dawn/dusk timing also align, it’s probably time to swing for the fences. Maybe that buck leaves its bed three minutes earlier than normal. That could put it 20 yards closer to the hunter’s treestand. Such differences aren’t significant when plotted on a scientist’s chart, but they’re overwhelming evidence to a hunter.

“All those factors are minor individually, but added together, maybe they sweeten things to boost a 2 percent chance to a 5 percent chance,” Kenyon said. “For a persistent hunter, that could be the difference between success and failure.”

A Guide’s Perspective
Longtime guide and MeatEater regular Remi Warren says he pays attention to moon phases when hunting elk and deer, but ultimately sees no difference in success rates during 10 weeks he guides elk hunters each fall.

“We hunt the full season, so we’ll always have weeks when we’re hunting the full moon,” Warren said. “When I look back over the past 10 to 15 years, it seems like we always hunt hardest during full-moon weeks. But I don’t think there’s a hard-and-fast rule. Each week has the same success rate because we know the animals so well. The best option is to just be out there every week, hunting all the time.”

Warren puts little stock in charts with daily rated predictions. “None of that ever seems too accurate,” he said. “It’s more about knowing elk behaviors for when you’re there, and knowing how to exploit those behaviors. If you hunt the final two weeks the same way you hunt the first two weeks, you probably won’t kill anything.”

When it comes to bear hunting, however, Warren zeroes in on the season’s last new moon and hunts the week with the least moonlight. “All we do that week is spot-and-stalk open areas,” Warren said. “During full moons, you just don’t see bears during the day. They might be moving around in daylight, but it’s not where we can see them. When we hunt that same place with no moon, we’ll see eight bears out feeding. It’s all or nothing.”

Differences like those might also explain why other people report increased deer activity at night during full moons, while most researchers do not. As Stephen Webb of Mississippi State University wrote in 2010: “Observational studies are confounded by … factors such as visibility, vegetation types, time of day, and observer presence. Without … night-vision optics, which were not available during earlier studies, deer would have been hard, if not impossible, to count during new moons. … Studies that remotely monitor animal movement or activity (with GPS collars, etc.) are preferred.”

Do Eyes Lie?
Woods said that’s why he dumped his Deer Activity Index and moved on. “Anything based on observed deer – what you see while hunting with your own two eyes – is biased,” he said. “You’re putting your best effort where you think you’ll most likely see deer. Meanwhile, a GPS collar follows that deer everywhere, 24 hours a day. And when you compare GPS data from about 300 to 400 deer in various studies on the same day in different locations, you see tremendous differences in observed vs. unobserved activity.”

Woods, however, doesn’t expect most hunters to agree. “I won’t hang my hat on anything that ties deer activity to moon phases or moon positions,” he said. “The better our scientific tools become, the less you see connections. There’s zero relationships with the moon. It’s the same straight line across the page. Hunters will hammer me for saying that, but they just don’t want to accept the truth about the moon.”

Feature image via Matt Hansen.