By C.J. Winand
For years, hunters have tried to accurately predict the best days to hunt and which ones would better be spent in bed. Could there be a scientific method to assure the good days from bad ones? Well, the answer is yes and it’s called the Deer Activity Index (DAI). What exactly is a DAI? A DAI is a tool that uses various moon characteristics to assist hunters and biologists in determining daytime activity levels among whitetails.
When I was young, my grandfather answered all my deer hunting questions. Although he would never reveal his actual method of analysis, his rationale for predicting deer movement went something like this; full moons were good and new moons (dark) were bad. Years went by and I started to test some of Pap’s wisdom, but, to no avail. All the scrupulous notes I had so religiously taken simply did not make any sense.
Then in 1991, while working on his dissertation, Grant Woods tried to determine if the moon had any effect on daytime deer activities. He worked with various astronomers in an effort to determine what moon phase or moon position had the best relationship to deer movements.
Through some extensive statistical analysis, Woods dismissed the moon phase and position components. Why? Because he found that the earth’s distance from the moon, plus the moon’s declination or degrees the moon is to the earth’s equator are very different from one full moon to the next. In other words, all full moons are NOT created equal. The same rationale also applies to quarter, half or whatever moon phase is present.
Using hunter compiled data in free ranging deer herds, Woods analyzed information on 6,009 tree stand hours, in which 5,686 deer were seen and 784 harvested. Other hunts from around the country were also added to the original sample size and checked with various moon orbit characteristics. Finally, after a lot of hard work all the statistical comparisons started to make sense. The end result is called a Deer Activity Index (DAI).
The DAI rates daytime deer activity movements into seven categories ranging from “4” to “10”. A ten reflects the highest deer activity, while a “4” indicates the lowest. It is important to note that when the DAI comes up with a “4”, there still will be deer activity. Although, it will probably be a slow day afield.
To satisfy any skepticism concerning the statistical analysis, Woods’ research showed that on days with a “8”, “9” or “10” (high DAI) values at a research site in South Carolina, hunters saw 76 percent more deer than on “4",“5” or “6” (low DAI) value days. Similar data occurred at a hunt club in New York. Hunters observed 54 percent more deer on the high DAI days than on low DAI days.
Similar results occurred for hunters that participate in drives! When the hunters at the club in New York started to drive deer, the data indicated 26 percent more deer on high DAI days compared to low DAI days. Intuitively, one would suspect no measurable or significant changes with drives, but this was not the case.
I asked Woods his thoughts on hunting during the midday hours while using the DAI? Woods stated, “I always stay in the woods as long as my schedule allows when I’m hunting. However, given similar conditions, I average observing significantly more deer during midday hours on “8”, “9” and “10” days compared to “4”, “5” and “6” days.”
Although there have been many studies correlating weather conditions to deer movement patterns, none of them are entirely consist with one another. Although not significant, barometric pressure seems to be the only weather parameter that is somewhat consistent with deer movements. As veteran hunters know, this generally occurs with an onset of a storm. Woods noticed this occurring during Hurricane Hugo in 1989. On the day prior to the storm (DAI value “4”), he saw nothing unusual. However, the day of the storm (which was also rated a “4”), Woods observed deer feeding under every persimmon tree, even mature bucks. Obviously, extreme weather conditions can have an influence on the DAI.
How is the DAI effected by extreme hunting pressure? Woods' states, “Unusually high pressure can override the DAI, but under normal hunting situations deer activities correspond very well.” Can you use the DAI values to determine the rut? The answer is NO. Findings suggest that there is no difference between the values when deer actually breed. In other words, breeding may be just as likely on a “4” day as on a “10”. If this doesn’t make sense, remember the DAI is for daytime activity only. On “4” days, breeding can occur, although it most probably occurs at night.
Exceptions do occur, in well managed herds with older age structures and balanced sex ratios the rut probably out weights any DAI. However, this is not the case in many parts of the country. As a result, the DAI is probably a better indicator of total deer movements in areas that experience a prolonged “trickle” rut.
Why does the DAI work? Some believe it has something to do with the moon’s gravitation pull. We know that the moon’s gravitational pull is different every day and the effects are felt through daily high and low tides. Some argue all living creatures are effected by the moon…just ask any bartender or police officer. For whatever the reason, the fact remains that the DAI is the only statistical tool we have to predict deer activity.
Woods believes, “I can now help hunters and researchers schedule their field time more efficiently by picking the best days to hunt. This should be especially helpful for those who have limited opportunities to hunt.” Testimony to this is reflected by letters sent to him stating, “By eliminating the least active days, my wife is happier due to the additional time I was able to spend with her,” or “It was almost as if the deer had made the activity schedule themselves and mailed it out to us hunters."
It’s important to note that the DAI does NOT tell you where to hunt, but a tool that indicates your most probable days for deer activity. Obviously, hunting know-how is still paramount in being consistently successful. The bottom line is this, if you have an hour to hunt, then hunt. But, if you have a DAI then you can modify your limited times afield to those key “8-10” days.