Why a barometer could be one of your most important hunting tools.
Everyone knows the old saying about being in the right place at the right time. Southeastern Ohio, a region known for big bucks, seemed like the right place for the onset of the rut last year. More specifically, I was on a piece of ground that’s privately owned and very well managed by my good friend Jeff Neal of Heartland Wildlife Institute.
On his land is a Banks blind overlooking a food plot I’d become particularly fond of over the previous three seasons, so much so that Jeff reserved it just for me.
It was looking like the timing couldn’t have been better. Just two days earlier, I’d endured the dynamic duo of Frankenstorm and Hurricane Sandy in the West Virginia mountains. When circumstances finally allowed, I crawled out and raced for the border, arriving in camp on the evening of Oct. 30.
Halloween can be a great time for an early rut bowhunt. Add nearly ideal weather – temperatures in the low 40s and intermittent light rain – and smother it in a departing storm with one of the lowest barometric readings ever recorded, and you have the ingredients for something truly special.
Deer movement on All Hallow’s Eve was fairly steady from first light until late morning, consisting mostly of young bucks, does and fawns. There was a bit of a lull from late morning to early afternoon. Then things really turned on and kept getting better.
The deer had obviously hunkered down during the storm and were now taking full advantage of the gradually improving conditions.
The afternoon wore on, and with daylight waning, I’d been watching a borderline buck for several minutes, repeatedly convincing myself to be patient. Then, the deer’s mood suddenly changed from dominance to submission.
Only one thing could cause that, so I grabbed my crossbow and set it up on the shooting sticks. Seconds later, a mature 9-pointer sauntered into the field, quartering within range.
I followed his progress through the scope for several steps before stopping him with a “blat” and pressing the trigger. The buck disappeared into the treeline just before I heard him crash.
I had finally hit that magical intersection of place and time. Finding the right place had taken three seasons. What made it the right time was a combination of random and uncontrollable factors, not the least of which was a rising barometer.
PRESSURE DROP
Although their motives vary, whitetail hunters and biologists are forever seeking greater insight into deer behavior, trying to figure out what makes them do the things they do. Knowledge improves our ability to predict what deer might do next, and when or where they might do it.
Hard scientific evidence is limited, but I’ve observed that barometric pressure – more precisely, a change in pressure – is one of the more reliable factors influencing deer movement.
In a North Carolina study, biologists captured 68 whitetails in four nights during a falling barometer, and 65 deer in 10 weeks of steady high pressure. Another study showed deer sightings increased dramatically at barometric pressures between 29.80 and 30.28 millibars, with the greatest activity during rapid pressure drops.
Meanwhile, numerous other studies have found little or no correlation between deer movement and rain, wind, moon phase and position.
So which is right?
NATURAL SELECTION
Being a biologist, I figure there’s a reason for everything, but it doesn’t take a Nobel panel to see the selective advantage for whitetails to increase activity around a falling or rising barometer.
Extreme weather poses a challenge to any creature’s survival and its ability to take in more energy than it consumes.
If an animal could predict bad weather, it would take steps to stock up on extra calories.
The same applies on the other end. If a buck has been hunkered down in bad weather for any length of time, it will be eager to find food.
Moving too soon could prove disastrous, however. The buck would need to know when it’s safe to resume activity. Animals that can predict such weather changes would have a better chance to survive and pass on a genetic predisposition to do so.
But how can they possibly predict such events?
The same way we do – by sensing changes in barometric pressure.
Humans use sophisticated scientific instruments, while animals rely on an innate ability possessed by all vertebrates, including us. Most of us just don’t realize it anymore.
With age come both costs and benefits. One cost is increasing aches and pains. A corresponding benefit is recognizing those as an opportunity instead of a problem. I’ve noticed my joints, particularly my left hip, begin to ache a day or so before bad weather arrives. When asked about this phenomenon, my osteopath explained it was a result of declining barometric pressure.
When the pressure against your body drops, joints and injured areas swell. This causes increased inflammation, and sometimes pain. It also causes subtle hormonal changes. We feel it but almost never recognize the cause, perhaps because our survival no longer depends on it. A deer’s could.
They don’t reason or take deliberate action as a result, but the falling pressure prompts a change in their physiology and behavior in somewhat the same way changes in daylight indirectly stimulate the rut.
Laboratory studies on other vertebrates have shown that declining barometric pressure stimulates food intake, suggesting they can sense and respond to it. The question then becomes, how do they react?
THE RISE and FALL
Years of observation have convinced me a falling barometer is better for hunting than a rising one. What little research exists seems to bear this out. I won’t speculate on the reasons, but deer activity seems to spike more before a storm than after. Timing of the activity spike can also vary with the size, speed and intensity of an approaching or departing front.
SQUALLS
Very fast moving fronts, or squalls, tend to produce narrow but intense activity spikes, a prime example of which I witnessed several years ago in West Virginia.
My hunting partner and I were headed into a piece of public ground when we noticed big, black thunderheads looming in the distance. Moments later a fast-moving front was upon us. For 15 minutes, the air was filled with gusting wind, torrential rain, thunder and lightning.
Then, it stopped just as suddenly as it started. You could literally feel the pressure rise. Sensing what might happen next, I raced to my stand. I barely had time to strap in before deer started feeding through, and it proved to be a very short hunt.
SLOW MOVERS
A slow moving front tends to produce a less intense but longer spike of activity, perhaps because deer have more advance warning. Conversely, they don’t have as much time to recognize and react to a fast-mover. Also, fast fronts are often smaller and pose less risk to survival.
The larger the depression, the more pre- and post-event deer movement you’ll see. I believe deer (and other critters) can somehow sense the intensity of an approaching storm and respond accordingly. But when does that happen?
THE LAG EFFECT
While chief wildlife biologist of the 825,000-acre King Ranch in South Texas, Dr. Mickey Hellickson studied the effect of several variables on daytime deer movement. Hellickson collected more than 420,000 observations from 43 collared bucks and found little or no correlation with moon phase, temperature, humidity or pressure.
However, Hellickson was looking at absolute pressure, not pressure change, and in so doing neglected to account for time lag. Remember, we’re interested in pressure change. By the time the barometric pressure bottoms out, the movement spike has abated.
I’ve found this to be particularly true with large snow events. Roughly 12 to 18 hours before a big snow storm, the activity has already decreased. The deer have filled their bellies and are bedded and ready to ride out the storm. They might stir a little and feed close to their beds, but they won’t move much.
On the other end, I’ve also noticed the first morning after a snowstorm is often dead. It can take a day or more before the deer are really back up and moving. Basically, they sense the change and seem to respond on the leading edge of a pressure drop and toward the tail end of a rising barometer.
Interestingly, I’ve observed a somewhat different scenario for rain and wind. It seems like after a prolonged windy spell or a passing squall, the deer can’t wait to get back to filling their bellies.
SYNTHESIS
That brings up another important point. All other things being equal, pressure changes by themselves might not have a strong or obvious effect on deer movement. But other things are seldom equal.
A departing low is often ushered out by an incoming high, which brings with it colder temperatures. The rising barometer and falling thermometer could conspire to produce above average deer movement. Conversely, a rapidly rising barometer is sometimes accompanied by high winds, which suppresses deer movement.
Virtually all the research has shown that regardless of the date or environmental conditions, deer move more at dawn and dusk. How much and how long they move varies. If an activity spike produced by changing pressure coincides with a normal activity peak, the effect is increased. Add another variable like the rut, and results can be dynamic, as my Ohio hunt proved.
CONCLUSION
We might never figure it all out, and I like it that way. The mystery is part of the allure. Never knowing for sure what a deer will do, even under the most controlled conditions keeps things interesting.
On the other hand, it’s also fun to try to predict what a buck will do, and then test that prediction by being in the woods. It’s not always difficult to find the right place, but with a better understanding of how different variables like barometric pressure affect whitetail behavior, we can make more informed guesses about the right time to be there.
Read Recent Articles:
• Why You Miss: Poor shooting isn’t always your fault ... but it usually is.
• Ignore the Opening Bell: While the chase phase of the rut is exciting, is it the best time to tag a mature buck?
• Be a Deer Caterer: Does supplemental food help whitetails?
This article was published in the Winter 2013 edition of Buckmasters Whitetail Magazine. Subscribe today to have Buckmasters delivered to your home.