The Science Behind a Deer's Sense of Smell & Scent Control

The Science Behind a Deer's Sense of Smell & Scent Control
Of all the whitetail’s superior defenses, the most reliable is its sense of smell. The olfactory system is equipped with 297 million receptors that decipher organic compounds within the air and then transfer data to the brain. Photo by Russell Graves

Understanding the science of a whitetail's scenting ability might not guarantee you a filled tag, but it definitely can't hurt.

On a brisk November morning in 2008, as I was running the video camera for my friend Chris Ellington in Clark Co., Illinois, we spotted a fat-bodied buck cruising up the ridge about 100 yards to our east. The chilly west wind was dragging our scent perpendicular to the buck’s line of travel, and we could tell the two were about to intersect.

”This ain’t gonna be good,” Chris hissed.

The big buck’s body language screamed “lovestruck zombie.” His mouth was open, his nose was almost on the ground, and he was doing the classic doe-seeking speed walk. In short, he was all but oblivious to his surroundings.

But when the buck hit our wind cone, his reaction was instantaneous. As if human scent had hit him in the face like an invisible baseball bat, the buck’s careless, rut-induced autopilot mode disappeared. He stopped in his tracks so quickly that his skin and fat shuddered.


The buck whipped his head, swinging his chocolate rack around in a whirl, and looked across the ravine directly at us. His black eyes were wide with alarm. It took all of about five seconds for him to take that first half-step backwards and then bail off the ravine away from us, blowing and flagging.


This episode was an example of how quickly a buck’s demeanor can change when human scent is intercepted. We all know whitetails possess excellent olfactory ability, and this buck offered but one example of it in action. Let’s examine the whitetail’s superpower sense of smell a little more deeply.


Defining Scent

So, what is scent? The answer gets a bit technical, but understanding scent and its origin is critical. After all, how can we as hunters attempt to control or eliminate scent if we don’t understand it on a biochemical level?

Biologist Dr. Bronson Strickland of Mississippi State University’s Deer Lab describes “scent” as a generic term for what’s known to chemists and wildlife researchers as volatile organic compounds (VOCs). He explains these substances originate as organic compounds given off by a subject. Due to their high vapor pressure, these lead to large numbers of molecules evaporating into the surrounding air.

VOCs entering the air can come from numerous sources. Manmade products such as gasoline, diesel fuel, paints, oil, tar and perfumes all give off unique VOC signatures. Plants give off their own VOCs when leafing, pollinating, flowering and growing. These signatures change throughout their annual growth cycle.


Our bodies give off literally thousands of VOCs. The human liver, kidneys, lungs and skin are all tasked with taking toxins from normal metabolism and rendering them chemically removable from our system through excretory pathways found in feces, urine, breath, sweat and saliva.

In one study, more than 1,800 distinct VOCs were determined to come from our body! Breath (872), skin and hair (532), feces (381), saliva (359), milk (256) and blood (154) made up the list, with some overlap among the compounds. Bacteria also give off their own unique VOC signatures on our body and clothes.

The take-home message is simple here: Normal body processes make us like a lightning rod projecting scent into the air in the form of VOCs. To put it frankly, we stink!


The Olfactory Pathway

Now that we’ve defined scent in its true chemical form, let’s climb into a VOC molecule and take a ride through a whitetail’s nose. Hold on tight.

A scent molecule is inhaled through the broad nasal openings and captured by little hair-like cellular projections called cilia in the mucous membrane. Once captured by the cilia, VOC molecules dissolve into and through the mucous and are transferred to the olfactory epithelium. Note: The whitetail epithelium is reported to have 297 million olfactory receptors. (The human epithelium has only 5 million.) These receptors translate the scent signal as electrical impulses up through nerves that extend through the roof of the mouth and into the part of the brain known as the olfactory bulb.

closeup of whitetail nose
Scent molecules are inhaled through the whitetail’s broad nasal openings and captured by hair-like cellular projections called cilia in the mucous membrane. From there, the particulates are dissolved and transferred to the olfactory epithelium. Photos courtesy of Clint McCoy

In another study, it was demonstrated that a whitetail’s olfactory bulb is about four times larger than that of a human. This means deer have a greater capacity to both detect and transmit scent signals to their brains. The olfactory bulb then shoots electrical impulses up the olfactory nerve into the limbic system of the brain for analysis.

So, what does the brain do with perception of scent? The answer here is dependent on the impulses received and the area of the brain affected. The amygdala and the hippocampus are parts of the brain’s limbic system that help the whitetail process sensory stimuli.

My colleague Dr. Rose Krupka, a veterinary neurologist, explains these areas of the brain by saying, “The limbic system is the primitive, unconscious part of the brain that has a direct connection to deer behavior, such as maternal instinct, mating, food selection and predator or threat aversion. The hippocampus is involved in instincts, learning and episodic memory retrieval. The amygdala communicates with the hypothalamus, where hormonal processes initiate the ‘fight or flight’ responses to fear or danger.”

What’s this saying? It means a deer’s nose is directly connected to the parts of the brain controlling memory, learning and self-preservation reflexes. Therefore, it would stand to reason that with age comes wisdom. A 9-year-old buck isn’t just theorized to be smarter than a yearling. Science says the longer a deer has lived in the wild, as scent experiences compound, the more the deer has learned how to avoid certain VOC signatures that signal danger.

We’ve all heard the phrase: “A mature buck is just a different animal altogether.” Well, neurobiology and anatomy of the animal makes this a sound assumption. With respect to scent, as deer age, their “smell library” becomes more defined. I’m convinced the whitetail’s super olfactory ability is what teaches them to stay out of trouble.

Clint McCoy with whitetail buck
Combining old-school woodsmanship with new scent-control techniques has proved highly effective for the author. A north wind and a southerly approach put him within range of this trophy buck.

The same thing happens with humans. For example, in human olfaction studies, the “Proust Phenomenon” has been used to describe the link between scent and involuntary memory. Ever smell a scent that instantly reminds you of an episode from your childhood? I have. In fact, every time I smell a certain pine scent, my brain instantly reminds me of Christmas when I was 3 years old. I received a red Radio Flyer wagon and a heavy, green John Deere die-cast combine toy as presents.

Extrapolating the Proust Phenomenon, if a whitetail buck here in the Midwest smells a certain VOC signature that reminds him of a near-fatal encounter with a hunter, it would stand to reason that the buck could involuntarily recall these scents and avoid similar situations like the plague.

Methods of Scent Control

At the risk of being blackballed by some of my peers in the outdoor industry, I’m just going to come right out and say it: A whitetail hunter can’t eliminate 100 percent of his or her human scent. Period. One can only hope to contain it.

Trying to beat the nose and brain of the whitetail’s olfactory system is like trying to beat the odds in a Las Vegas casino. You might have a couple good nights at the blackjack table or hit a few slots for some coin, but statistically the house always wins.

Fortunately, as hunters we don’t have to win every hand to have a good deer season. So just how can we minimize our VOC signatures? Let’s examine some of the basics:

Bodily Hygiene

Taking a pre-hunt shower with scent-free soap has become standard operating procedure for most serious whitetail hunters. This helps reduce VOCs that are given off from bacteria that cause body odor.

Unscented, prescription-strength antiperspirants are a great way to keep armpits dry. I’ll even apply to my feet and groin to reduce moisture and bacterial growth in these areas. Brushing teeth with baking soda-based toothpaste is also in my bag of tricks. But as stated above, our breath constantly gives off VOCs in real time, so this step might be of limited value.

Clothing

Keeping all clothes associated with our hunting adventures laundered in soaps free of fragrances and UV brighteners is a good idea. I store mine in an airtight tote and dress in the field before each outing. This is tedious in the dark on a cold December morning, but it beats smelling like the gas station or kitchen.

Some clothes are designed to be scent-reducing, using activated carbon or silver-impregnated fibers to help absorb or reduce bacterial-derived scents. I’ve used them all. I’m not sold on the idea they significantly reduce human odor, but wearing them certainly can’t hurt if they’re kept clean.

In recent years, I’ve been using more natural fibers like wool or wool-blended outerwear, as I feel these fibers are naturally resistant to odor propagation. These fabrics give off their own unique odor, which I find to be beneficial even when they get wet.

Footwear

Of all the items I take to the woods on a hunt, I’m most stringent about my boots and how I care for them. I almost always wear knee-high rubber boots instead of leather lace-ups as a way to reduce the level of foot odor projected onto the landscape.

I’m a freak about how my boots are stored. I always keep my boots in a separate airtight tote in the bed of my truck. They’re never worn while pumping gas, while on asphalt or concrete, or in the house or garage; the only thing they ever touch is Mother Earth. I pack a pair of tennis shoes and swap them truckside for my boots before a hunt and vice versa afterwards. I place some corn husks or stalks into the bottom of my boot totes to add a cover scent effect to them. I’ll usually dry them a few times a week with a boot dryer that lives on my front porch to eliminate bacterial growth and odor on their insides.

Why am I so picky about my boots? I feel they’re the only hunting item that’s in constant contact with the whitetail’s environment. The cleaner they are, the less I worry about my scent trail on hikes to and from my tree stands. Using this protocol, I’ve clearly seen a reduction in the number of times a buck or doe has cut my entry track into the timber and hit the danger alarm.

Scent-Eliminating Sprays

The industry is full of scent-eliminating sprays, and deer hunters purchase untold gallons each year. Some of these sprays advertise a 99 to 100 percent efficacy in eliminating human odor. Is that possible?

“It is unreasonable to think pre-hunt application of these sprays can eliminate 100 percent of human odor, given the various sources and volume of VOC molecules given off by the human body,” claims Dr. Strickland. He does yield to the idea that these sprays can and do eliminate a few of these key VOCs — so again, using them presumably can’t hurt.

I used to buy these sprays ad libitum and applied them religiously. But in recent years I’ve relied more heavily on ozone scent-elimination technology to reduce my odor footprint.

Cover Scents

Many old-timers sprayed skunk or fox urine on their boots in an attempt to beat a whitetail’s nose. Nowadays, vanilla-based sprays are available for the modern hunter who’s trying to do the same thing.

Various deer-based urines and roll-on sticks also are popular with hunters. I’ve used ConQuest Scents’ EverCalm a fair bit, and I’ve observed several downwind deer reacting favorably when I’ve employed it properly. I feel that with the advanced scent palate a deer has, cover scents as a group are a bit ambiguous in their degree of efficacy. The likelihood a mature deer can eventually decipher through the smoke screen of most cover scents seems high to me, though.

Ozone

When I was in college, I helped a couple graduate students gather data for their thesis studies on the use of ozone in some of the smelliest places on earth: swine-confinement buildings. These students were pumping ozone into hog buildings, and I’d collect air samples from the treated barns for them to analyze in gas chromatography studies.

The idea here was to use the chemistry of the ozone molecule to bind to VOCs to help eliminate odor in these operations. The results? It worked. The chemistry of ozone allows the molecule to ionize and bind to VOC molecules and render them less aromatic. Science supports this to hold true. But the scale of running so much ozone in such large buildings made the endeavor too costly to operate.

With marked skepticism, I began using the popular Ozonics brand field generator two seasons ago. I’ve taken it on nearly every single hunt for two full seasons and have had excellent results. When a deer encounters my wind cone treated with ozone, it seems to engage the scent, halt, sniff the air and hang out for a bit instead of blowing or stamping a foot in alarm.

The buck I arrowed in November 2017 was directly downwind at 40 yards, and he lingered just long enough for me to pull off the shot. It was as if the ozone fogged his ability to decipher my VOCs. I’ve since had similar experiences and feel these units are scientifically sound and have proved their worth, based on my in-field observations.

I also like the ability to “Dri-wash” my clothes between hunts if time doesn’t allow for full laundering. But however you use it, make no mistake: Ozone technology is here to stay. I feel this stuff works and allows me the freedom to hunt more aggressively and cheat the wind at times. Is ozone the magic bullet for scent management? No. Can it help in the field? I say absolutely.

Old-School Woodsmanship

The most important scent-mitigation method is as old as time: To beat a buck’s nose, it’s best not have him get your wind in the first place. Just as was true long before the modern era of deer hunting, staying downwind of our prey is paramount to staying undetected.

Be it while scouting, entering or exiting a hunting area, sitting in a stand or still-hunting, playing the wind is always smart. Understanding how wind travels along structure lines such as field edges or ridgetops is important. Planning for the rise and fall of thermals is another critical aspect of scent management.

Various products exist to aid in gathering this information. Wind-checking powders and vapor gadgets work well, though they can be limited in their projection distance. Milkweed seeds are a favorite floating wind indicator for a large number of diehard wind nuts. However, I use none of the above.

You might snicker, but I never leave home without a small bottle of child’s party favor bubbles. A stream of dozens of bubbles on the airways can be seen floating for great distances in the timber and gives a phenomenal indication of how wind moves around a structure or obstacle. I carry my bubble bottle on every hunt and post-season scouting trip. With enough judicious use, I can use these little bubbles to get a “wind flow map” of a certain stand site, ridgetop, creek basin or other point of interest for each wind direction on the compass.

The results have proved to me that the forecasted wind direction for the day can have quirks or swirls the naked eye is unable to see but a deer is able to detect. Laugh all you want, but you’d be surprised by what you can learn from these little bubbles!

In Conclusion

We understand the greatest defense a mature buck has is his superior olfactory ability. These animals have evolved to use both their noses and their brains to avoid putting themselves in harm’s way. A grasp of the chemical sources of scent in the form of thousands of VOCs is excellent information to use in one’s personal scent-mitigation strategy. Likewise, understanding the neurobiology involved in scent processing at the level of the whitetail’s brain is important.

Olfaction is an intricate system we hunters must think about critically in order to tag mature bucks on a consistent basis. So the more we know about what the nose knows, the better.

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