Are Hunters Being Loony About Lunar Phases?

Growing up in eastern North Carolina, I spent an irresponsible amount of time watching the world from a deer stand. Rifle season for whitetails in eastern North Carolina runs mid-October through the New Year, and you could generally find me in one of three places during that 2.5-month span: in school, on a football field, or twelve feet up an oak tree.

Like many young folks, my overconfidence in my knowledge of how the world works rivaled my eagerness to shirk chores to spend time in the woods. One facet of this adolescent conceit was my understanding of how the moon impacts deer. I was a voracious reader and had gleaned a vast collection of tips and advice from hunting books and magazines like this one that set me apart as a uniquely talented outdoorsman in my own mind. But among all these, two facts featured most prominently: (1) deer became less nocturnal around the new moon, and (2) the rut peaked during the full moon in late November. So all season long, I kept a close eye on the moon and spent even more time hunting during these golden windows of opportunity.

I moved west after college for itinerant wildlife biology work and then graduate school in the same subject, and with the shorter western hunting seasons and larger responsibilities of adulthood, I thought less and less about the moon’s influence on game animals. If I had a tag and a free weekend to hunt, I hunted—rain, snow, sleet, or shine.

After a decade of moving from place to place, though, I landed a permanent job a couple of years ago as a professor of large mammal ecology at the University of Arizona. My position is research-focused, so while many of you reading this article spend your workdays thinking about what makes big game tick, I’m in the lucky position of getting paid to do it. And in my efforts to merge my personal and professional pursuits, I started thinking about the moon again recently. What does science say about how the moon influences big game (and downstream of that, potential hunting success)? All else equal, should I be thinking about moon phase when I’m putting in for tags?

3 Main Theories Floating Around

Before I get into the specifics of research findings, though, I want to explicitly lay out some ideas because I think describing them makes for more rigorous thinking about this topic. In reading and talking about hunting and wildlife biology, I have come across three main theories for how the moon might influence animal activity.

First, the most prominent difference people notice between phases of the moon is the amount of lunar illumination—nights are darker during the new moon than the full moon. Because of this difference in the amount of light available at night, animals may shift their daily cycles of activity to spend more or less time active at night vs. during the day. But there are tradeoffs—when it is darker, it is harder for animals to see, but also harder for their predators to see.

Second, some folks think animals move more at certain times of the lunar month. In other words, animals might not only move at different times of day as the moon changes, but they might move more, period. This would probably be due to light levels, because having more light across the whole 24-hour period might open up more opportunities for movement. But the relevance of this to hunters isn’t quite as clear to me as Idea #1—if animals are moving the same amount during the day and more at night, that doesn’t really change things for hunters.

Third, some people think that rather than the moon’s illumination, it’s the moon’s position that influences animal movement. I’ve never heard a clear biological explanation for why this might be the case, but the moon’s gravitational pull famously causes the ocean’s tides, so it isn’t crazy to think that this immense invisible force might influence animals more than is obvious to the eye. However, you need to be careful about untangling lunar illumination from the moon’s position, because the position of the moon in the sky at a given time of day is directly related to how much is illuminated—the full moon always rises around sunset, the new moon around sunrise, and the quarter moons at midnight and noon.

Study Methods

It's also worth thinking about the techniques we use to study this topic. The most common methods for studying large animal activity are trail cameras and GPS collars, and there are more trail camera studies than GPS collar studies because you can study more species more cheaply. These two methods give you slightly different data, though: trail cameras provide coarse data on animal activity across a whole population (even when individuals are identifiable, like a big buck with a unique rack, you likely won’t get many photos of it, and likely only at a few locations). GPS collars, on the other hand, provide data on individual animals and at finer scale. Because animals must walk in front of a trail camera for it to collect data, animals that are active but moving locally (like a deer foraging in a staging area) won’t be detected as often as animals moving longer distances ( even though they are still active. So for this particular research question, I think trail camera data is good, but GPS collar data is the gold standard.

Overall, there is quite a bit of research on this topic across mammals in general. The most frequently cited paper on this topic is an overview paper published in 2014. The authors of this paper found 58 studies on nocturnal activity by mammals, and their results were interesting at first glance. First, they found that predators that generally use vision more than other senses typically became less active at night as lunar illumination increased, while visual prey species became more active. Moonlight didn’t seem to affect species that mostly use other senses (e.g., hearing and smell). Second, as lunar illumination increases, species that tend to live in more open habitats tend to reduce nocturnal activity more than those that live in thicker cover. Unfortunately, however, most of the studies these researchers found were focused on small mammals like rodents, bats, and rabbits—only one of these studies focused on ungulates, a 1990 study of white-tailed deer in Michigan.

Stagnant Data?

Has there been new science published since then? Unfortunately, there still isn’t much. After an intensive search, I found four total peer-reviewed papers on responses by big game to moon phase, all on white-tailed deer. Of these four papers, one collected data with trail cameras, one with VHF telemetry (an older animal tracking technology that requires manual triangulation of animal locations), and two with GPS collars.

The trail camera study took place in 2014-2018 in eastern Texas and tested whether deer moved more at night during different moon phases if you account for cloud cover. This is a combination of ideas #1 and #2 mentioned above, but the authors didn’t really test either—the data only included nocturnal activity, so there was no comparison with daylight movement rates (necessary to test #1), and did not capture the full day of movement rates (necessary to test #2). This study purported finding that deer moved more at night when the moon was full and nights were clear, although I do not think their statistical results actually showed this happening for wonky reasons I won’t go into here.

The VHF telemetry study took place in 1981-1984 in southern Michigan and tested idea #2 mentioned above. These researchers found that deer activity slightly decreased in spring on days when more of the moon was illuminated, but found no effects of the moon at any other times of year.

That leaves the two GPS studies. The first of these took place in 1998-2004 in central Oklahoma and tested both idea #1 and idea #2. These researchers found no support for either idea—deer moved at about the same rates and at about the same times across the lunar month.

The other GPS study took place in eastern South Carolina and tested idea #3. This group of researchers reported that deer were more likely to move during moon underfoot and moon overhead periods during quarter moons, and moonrise and moonset during new moons and quarter moons. However, because of the relationship between lunar illumination and when the moon rises and sets, this basically means that deer are most active around sunrise and sunset—something I don’t think anyone would dispute. Furthermore, although these authors don’t focus on it, minor analyses in this paper inadvertently show that moon phase does not alter movement at any time of day across the lunar month (ideas #1 and #2)

Predatory Shifts

Moon phase and position may not matter much for deer, but what about predators? Since we have so little science on game animals, scientific evidence on how predators respond to lunar illumination may be able to inform how we would expect their prey to behave to avoid them. And there is a small amount of data on this: there are two studies on the effects of moon phase on pumas, both using trail cameras in Central America (Mexico and Belize) and both testing idea #1. Neither study found any evidence that pumas shift their activity in response to moon phase.

So to summarize, there are four studies of deer, which between them test idea #1 twice, idea #2 three times, and idea #3 once. None of the studies provide meaningful support for these ideas. There are also two studies that look at idea #1 in pumas. But these don’t show any evidence for moon phase affecting their activity patterns either. So although there isn’t much peer-reviewed science on this topic, the little research that has been published indicates that there are no major patterns linking the moon and activity of big game species.

I would end the article there, but my search through the scientific literature sparked my curiosity—I am genuinely surprised that there is this little science on this topic. What if there were relationships that just hadn’t been published yet? One of my graduate students is using a nationwide data set of trail camera photos called Snapshot USA for her graduate research, and this data set is already set up to test idea #1 for quite a few species.

Correlation

I couldn’t resist the opportunity to do a quick-and-dirty analysis of this idea for white-tailed deer, mule deer, elk, moose, and black bears—nothing I could publish but something that would reveal any patterns large enough to inform hunting strategy. The results were underwhelming: I did find statistically significant relationships between lunar illumination and activity of white-tailed deer and black bears, but the odds of a deer photo being taken at night increased by only 3% from the new moon to the full moon, and the odds of a bear photo being taken at night increased by only 5% from the new moon to the full moon. Lunar illumination had no influence on nocturnality of any other species.

So what should a hunter take home from all of this? There isn’t enough evidence to say the science is settled on this topic, but the little science available indicates effects of the moon on big game activity are minor at best. There is little enough data that I could be swayed by good studies in the future, but I would be surprised if the moon had much of an effect on big game, and even more surprised if it was large enough to create a meaningful advantage for hunting. As is often the case, there is no substitute for hunting hard and often.

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