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The Science of Canine Scent

Your dog's nose knows, but how exactly does his sniffer work?

The Science of Canine Scent

Let’s take a deep dive into understanding your dog’s complex sense of smell. (Photo By: Scott Linden)

All people and animals have a dominant sense, and that’s what makes the hunter/gun dog combo so powerful. People have great vision, while a gun dog’s sense of smell is in the top one percent of all animals. Send a Lab on a blind retrieve and he’ll return with a duck. Cut a bird dog loose in a covert, or a flusher or versatile dog in a field and if there is a bird there, they will deliver. We go together, like peas and carrots.

The dog’s sense of smell is the key to our combined success. But bears, elephants, sharks, and rats also have a keen sense of olfaction, and their ability to discern scent is what has helped them locate food not only to survive but also to thrive. Training a rat to locate pheasant or an elephant to smell an IED isn’t practical, but working with man’s best friend is a joy. How the dog’s nose works exactly is often overlooked, especially because it’s such a fascinating body system.

The Think Tank   

Paul Waggoner, the co-director of Auburn University’s Canine Performance Science program, has been studying how dogs smell for nearly three decades. “Our program began over 30 years ago,” he said. “It was founded after a terrorist placed a bomb aboard Pan Am Flight 103. The bomb exploded over Lockerbie, Scotland, and the entire crew and passengers, many of whom were students returning home for Christmas, were killed. We began pioneering efforts with dogs in the early 1990’s because they are inherently great scent detectors. Odor guides their behavior which is why you now see them working at airports and other highly trafficked, public places. Their 300 million olfactory receptors far eclipse the six million found in humans and makes them essential for locating IED’s in the military’s Off Lead Down Range detection program. We’re constantly studying the detection capabilities of dogs along with their other unique abilities to help prevent future tragedies from occurring.”

Hunters Knew it All Along  

Waggoner uses a number of different gun dog breeds in his program. Dogs from successful field trialing and hunt test campaigns especially exhibit behavioral characteristics for detection tasks. Their behavior represents the highest levels of odor-guidance, and they’re more durable at work.

According to Waggoner, “We started with Labrador retrievers that were gifted to us by Australian colleagues, and they have become the cornerstones of our detection dog program. Their strong olfactory capabilities come with a calm, biddable temperament, and Labradors are adaptable to many detection tasks. They’re seen by the public as friendly, which can be a benefit in many circumstances.” Other sporting breeds that are gaining in popularity are German shorthaired pointers, German wirehaired pointers, vizslas, English field cockers, and golden retrievers.


Rock What You’ve Got   

According to Russ Kelley, the Eukanuba Scientific Services Nutritionist, “Humans are visually guided. People can discriminate between a capital R and a capital P, for example. Go to the paint section in a hardware store and you’ll know that we’re highly capable of discerning color, too. Watch a wide receiver make an over-the-shoulder catch and you’ll know we have excellent depth perception and great hand/eye coordination. Dogs have that same sensitivity with their noses as they are odor detectors and odor guided.

“A small group of people have such a refined sense of smell that they’ll find careers like a sommelier, or a professional wine taster. But even that person’s sense of smell pales in comparison with a dogs. A canine’s sense of smell is between 10,000 to 100,000 times better than that of a human. It is so keen that dogs can detect the equivalent in air of one drop of Kool-Aid in a swimming pool filled with 75,000 gallons of water.” It is one way they find birds.

duck hunter giving hand signal to black labrador retriever in swamp
Although they also use their eyes to hunt, sporting dogs rely mostly on their nose to locate birds through scent. (GUN DOG photo)

The Dog’s Nose is Unique  

Another way dogs find birds is based on how they sniff, which is constant. “The way to describe the start of the dog’s smelling process is best described by amplitude and volume,” Waggoner said. “Amplitude is the speed at which air is brought into the nose while volume refers to the amount or quantity. A human’s nose processes smell in what is called a low amplitude/high volume manner. A person will inhale or sniff once or twice but that volume of air is large. A dog’s nose works totally opposite. A dog will inhale six to seven times more and faster than a human, but each sniff moves a much smaller amount of air. Those fast sniffs of low amounts of air place them in a high amplitude/low volume category. The key here is that those shorter, higher-frequency sniffs provide dogs with more detailed information about an air sample. An increased amount of information provides for higher resolution of processing. Dogs have superior odor discrimination, and when trained they can track that odor to its source.” It’s why well-bred and well-trained gun dogs are so coveted by hunters, field trialers, and hunt testers.  

Another important way the dog’s nose works involves its unique physical structure. Look particularly at the slits on the side of the nose. “When a dog inhales, air passes through the nostrils,” Waggoner said. “It then gets separated into two parts. Some of the air continues into the lungs for respiration, while the second part goes to the back of the nose for an initial scent analysis. All inhaled air must be exhaled, and when the air is exhaled, it doesn’t pass the way it came in. Instead, it goes through the alar folds, the technical name for the slits. Because exhaled air is pushed through those nasal slits on the side of the nose, old air is prevented from being co-mingled with new air. There is far less dilution of scent, and the information in a new sniff is preserved as unique. The alar folds have been shown to create a slight vacuum effect which allows each sniff to sample a larger area. That distinction is important as it contributes to the dog’s olfactory sensitivity, selectivity, and ability to accurately perceive a concentration gradient allowing it to track an odor to its source.”

brown and white English pointer dog on point in grassy field
If you think you know better than your dog, just remember your dog's 300 million olfactory receptors far eclipse the six million that you have. (GUN DOG photo)

After air passes through the nostrils, it is channeled to the back of the muzzle into the olfactory recess where it hits a number of turbinates. “Turbinates are small bones that are covered with mucus membranes,” Waggoner said. “The turbinates contain an olfactory epithelium, or surface tissue, that contains and estimated 200-300 million olfactory receptors. Those receptors channel information through 600,000 neurons which is 300 times those of a human. Information from the olfactory epithelium is passed along to the olfactory bulb which then goes to the brain. A dog’s olfactory bulb is forty times the size of a humans. It’s easy to see why scent information is processed faster and more thoroughly in dogs than in humans.”

But we know dogs have an outstanding sense of smell. Understanding how dogs interpret smell is more difficult to understand. “The physical dimensions related to some senses, especially vision and hearing, are more readily understood,” Waggoner said. “We can determine the wavelength and intensity of light to better evaluate vision. We can do the same for hearing. But due to the complexity of smell, it’s very difficult to pinpoint how dogs interpret smell. We can understand the chemistry of an odor, but we can’t always tell how the brain evaluates it. That’s especially true with the low-odorant content that comes from many items. Scientists and researchers lack the instruments to truly understand the specifics of the dog’s sensitivity of smell.”

While dogs are renowned for their olfactory sensitivity, it is also their selectivity, or ability to discriminate between chemically similar odors and their very high signal to noise capability that contributes to their ability to perform detection tasks. “Dogs demonstrate a truly remarkable capability to detect a very small amount of a specific odor (needle) in a very odor noisy (haystack) environment. A comparison might be being in a large auditorium with lots of people talking loudly and being able to pick out the distinctive tone of your spouse’s voice from the opposite side of the auditorium and then using sound to locate her in that room.”

german shorthaired pointer in mountains
Cold and damp conditions are the most ideal for a gun dog's nose sensitivity. (GUN DOG photo)

Scent Memory  

The information from the smell of what dogs are looking for is stored in the brain for qualification. “Research has demonstrated that both people and dogs remember odors for significantly longer periods of time than sights or sounds,” Waggoner said. “Think about it; if you got sick eating a particular type of food and then catch a whiff of that same type of food, your stomach turns, doesn’t it? That is because your brain remembers that smell as having provided a negative response. But if you return to your childhood home after a long absence and are surrounded by those wonderfully familiar smells from childhood then you’ll smile.

Dogs remember smells, and they go through an incredibly fast process of elimination so as to arrive at their goal. In my line of work, those past associations contribute to them finding a bomb or a drug, while in a sportsman’s life it is how the dog locates a covey of quail, a pheasant, or a duck. Dogs’ memory for scent is incredibly resilient.”

Bird Scent  

Poor scenting conditions are usually cited when dogs have a tough time finding birds. Hot, dry, windless days usually means dogs run over birds. A hard-hit bird may be considered ‘air washed,’ leaving little if any scent on the ground. Foot scent comes from running birds, while body scent comes directly from the bird. Without question, cool, windy, and moist days make it easier for a dog to find birds.

But one overlooked issue comes from a dog’s physicality and condition. Russ Kelley says, “Panting, or the exchange of internal air for external air, is a way dogs cool down. We love running dogs on cool days because the cool, wet weather makes it easier for dogs to regulate their body temperatures. Running unconditioned dogs on hot, dry windless days causes them to pant, and when they’re breathing through their mouths, the air is not being processed through the nose. That may be a reason dogs run over early season birds or have a tough time finding others, and that’s why it’s important to condition your string before the opener. It’ll give them a greater opportunity to succeed.”  


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