Understanding and fooling a deer's sense of smell

There are tons of examples of hunter-deer encounters involving smell. Ever been sitting in your stand and a deer you can't even see 150 yards away starts to blow? We've all experienced that one. Last year I watched a coyote cross a field. The next morning a buck was crossing that same field and stopped short, right where that coyote had walked. Of course, bucks can do that where we walk, too. As I said in the chapter on scents in my book, "Whitetail Advantage," a deer's nose knows.

Why is a deer's sense of smell so much better than ours? There are no major studies done on deer that answer these questions, but there have been studies on humans, mice and insects that give us some good ideas on how this works.

Scents And Odors

The interior of a deer's nose has hundreds of thousands, if not millions, of nerve cells. And there are groups of these cells that are very similar, and many different groups of similar nerve cells are found scattered around the inside of a deer's nose. In fact, there are probably thousands of groups of cells in the nose, and each group can detect one odor. This means that a deer has a group of cells in its nose that can detect acorns, and others that detect alfalfa, and corn, and certain twigs, and dead leaves, and dogs, and other deer, and human deodorant, and gasoline on gloves, etc., etc., etc. You name the odor, and a deer has a group of cells located in one tiny region of the nose that can smell that odor.

Once that odor hits those receptor cells, it triggers an area of the deer's brain. To simplify this, when a deer smells an acorn (for example), that activates the acorn nerve cells in the nose, and that then sends a message to a part of the brain, and that leads to a pattern of behavior. Therein lies the key to how deer get you. An odor, one odor, triggers a deer behavior.

If a young deer has a bad experience with a dog, a pattern of behavior is created in that deer's brain. The next time that deer smells a dog, the deer flees. But if this deer grows up in a park where there is no hunting, and people walk their dogs on a chain all the time, then a dog's odor probably won't trigger that negative response.

Pursuing that idea further, if a deer grows up in an urban environment (as millions now do), then the odors it smells related to humans won't trigger a negative response. But if that deer first smells a human odor in the wild, and that initial encounter was negative (e.g., the deer got shot at with a gun), then the moment it gets a whiff of that same human odor again, the deer bolts out of there.

A unique odor can trigger distinct memories in humans, and in deer. I remember growing up that the smell of cooked onions really was a negative for my appetite. It took several years of my adult life for me to retrain my brain to have a positive response to that odor. I'm glad I did, because I now like cooked onions. Enter the old, big buck. If we look at a buck that has had several negative responses to the presence of humans, and some human odor, it is obvious that as that buck ages and has more negative encounters, a pattern of behavior is reinforced over and over. He has had many negative encounters and created a lot of patterns of behavior related to odors, and he survived them. With each passing day, week, month, year, that buck becomes harder and harder to see and get close to, much less shoot. He probably becomes more secretive each time he has a human encounter. Obviously older, bigger bucks that have fast response times to any negative odors survive longer in the wild. That's why they are older and bigger.

One neat question is why certain receptor cells inside a deer's nose pick up an odor, while all the other millions of receptor cells ignore that odor? At least one study has been done that answers this question, and it involves genes. It's way too complicated for my simple brain to understand, but the bottom line is that genetics plays a major role in how deer smell. Genetics is involved in why certain groups of cells in a deer's nose respond to the smell of a dog, while others respond to the smell of acorns, or humans, or whatever. Those details aren't all that important for hunters to understand, but the fact that individual odors can cause a deer to respond in a certain way is very important, and genes play a role.

Here's a question. How many negative human encounters does it take to make a buck totally nocturnal in the fall? I don't have an answer, and it is doubtful that any scientist ever will, but there is a number. That number of encounters probably varies for each individual buck.

Deer lick their noses all the time, especially bucks during the rut, because odor particles stick to a deer's nose better when it is wet. Wet weather might also enhance the ability of a deer to recognize an odor. I love to bowhunt on mornings when there is a mist in the air, but be aware that a deer's sense of smell might be enhanced at such times.

What To Do About It

Where I'm headed with all this is obvious. We need to reduce human odors as much as possible. At this year's Archery Trade show in January, there was a new line of hunting clothes released that has a synthetic odor-reducing layer. I sat through a seminar on this new product and it was impressive to say the least. Yes, I'm a believer that certain clothes can reduce human odors. And I'm definitely going to try this new line of scent-reducing clothes.

I also believe in scent spray, and scent eliminating products such as scent-free soap, shampoo, deodorant, scent-reducing detergent, etc. I use them all. I store my clothes in a special outbuilding, away from my garage and other human odors. Yes, they are stored in special bags and boxes, and I use these as much as possible when I'm away on hunting trips.

We've often heard that the best chance for success on a big buck is the first time you sit a tree stand. I believe that, and I believe it is about odor. Reusing a stand means more odors in the area. A guide I hunted with in Montana many years ago told me that deer are not smart; they just have great reaction time. I never fully understood that until I found the research reported here. That reaction time is all about odor and patterns formed in reaction to odors. Deer can react to those patterns in milliseconds. Gotcha.

Oh yes. What about a deer's sixth sense? We've known for 80 years that humans give off measurable energy. And there is proof that red deer can sense electromagnetic radiation. Does that mean that deer have a sixth sense and can feel our presence? Probably, but let's leave that for a future column. Just another challenge presented to us by the fantastic senses that whitetails possess.

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