The canine nose…truly one of nature’s most
amazing accomplishments. A dog’s nose not only dominates her face,
but her brain, as well. In fact, a dog
relies on her sense of smell to interpret her world, in much the same way as
people depend on their sight. Although
this contrasting world view may be hard to imagine, know that your dog
interprets as much information as you do.
However, she does much of this by smelling an object or animal, not by
staring at it. (Stanley Coren, Sarah
Hodgson, Understanding A Dog’s Sense of Smell).
This article is Part 3 of our series Understanding Bird Scent. In Part 1, we discussed how scent is created on a game bird. Part 2 was all about how the bird scent is diffused into the air. In Part 3, we’ll discuss the receptor of all of this scent…the dog’s nose. This entire article could be just about the anatomical structure of the canine nose, however, that might be boring. So, we’ll discuss briefly the anatomy of the nose and then discuss how that anatomy works and how it compares to the human olfactory system.
When reviewing the anatomical structure of the canine nose, we encounter the nasal plane, vomeronasal organ, turbinates, sinuses, nasal mucosa and olfactory cells. For our purpose, we’ll primarily discuss the turbinates. A microscopic view of this organ (turbinates) reveals a thick, spongy membrane that contains most of the scent-detecting cells, as well as the (olfactory) nerves that transport information to the (olfactory lobe of the) brain. In humans, the area containing these odor analyzers is about one square inch, or the size of a postage stamp. If you could unfold this area in a dog, on the other hand, it may be as large as 60 square inches, or just under the size of a piece of typing paper. (Stanley Coren, Sarah Hodgson, Understanding A Dog’s Sense of Smell). Almost one eighth of the dog’s brain and over 50% of the internal nose is committed to olfaction, whereas the human olfactory lobes are very much smaller. It is the brain that odors are recognized, interpreted, and filed for memory. William G. Syrotuck, Scent and the Scenting Dog, 1972).
Here’s more: The anatomy of a longer nose produces more scent receptors and greater scenting ability. For example, a human has five million scent receptors and a beagle (longer nose) has 225 million scent receptors. …while we might notice if our coffee has had a teaspoon of sugar added to it, a dog could detect a teaspoon of sugar in a million gallons of water, or two Olympic-sized pools worth. Another dog scientist likened their ability to catching a whiff of one rotten apple in two million barrels. (Alexandra Horowitz, Barnard College). If you make the analogy (human to dog), what you and I can see at a third of a mile, a dog could see more than 3,000 miles away and still see as well. (Peter Tyson, Dog’s Dazzling Sense of Smell, NOVA ScienceNOW, 2012)
We’ve established the superiority of the canine nose over the human nose, now let’s examine how the actual function of the nose differs between dog and man. When humans inhale, we breathe through the same airways (olfaction and respiration) within our nose. When dogs inhale, a fold of tissue just inside their nostril helps to separate these two functions (one for olfaction and one for respiration). (Peter Tyson, 2012). The air humans smell simply goes in and out with the air we breathe.
In dogs, about 12 percent of the inspired air, Craven’s (Brent Craven, Pennsylvania State University) team found detours into a recessed area in the back of the nose that is dedicated to olfaction, while the rest of the incoming air sweeps past that nook and disappears down through the pharynx to the lungs. Within the recessed area, the odor-laden air filters through a labyrinth of scroll-like bony structures called turbinates. Olfactory receptors within the tissue that lines the turbinates, in turn, “recognize” these odor molecules by their shape and dispatch electrical signals to the brain for analyses.
When we (humans) exhale through our nose, we send the spent air out the way it came in, forcing out any incoming odors. When dogs exhale, the spent air exits through the slits in the sides of their noses. The manner in which the exhaled air swirls out actually helps usher new odors into the dog’s nose. More importantly, it allows dogs to sniff more or less continuously. In a study done at the University of Oslo in Norway, a hunting dog holding its head high into the wind while in search of game sniffed in a continuous stream of air for up to 40 seconds, spanning at least 30 respiratory cycles. (Tyson, 2012).
Regarding the above: This ability is due to the Bernoulli effect, which results from lower pressure in the mouth cavity than in the nose during inhaling and causes an inward flow of air through the nose. This phenomenon only occurs while the dog is running with its head held high and does not occur while it is resting or searching for ground scent. This phenomenon explains why dogs can be running and breathing hard (panting) yet continuously scent game. (David K. Dahlgren, Use of Dogs in Wildlife Research and Management, Utah State University, 2012)
Let’s summarize how the canine and human nose differ and why those differences make the canine nose so superior. The canine nose has far more scent-detecting cells, the canine nose separates inhaled air for olfaction and respiratory use which keeps olfaction air more pure. And, the percentage of the brain used for olfaction interpretation is much higher in a dog. The canine nose is the winner…hands down.
Throughout researching for this three part series, a common thread kept surfacing…a dog’s health. A physically fit dog, both exercised religiously and fed properly for a canine athlete, will perform better. For a variety of health-related reasons, many bird dogs experience olfactory difficulties (Holloway 1961, Myers et al. 1988); having no sense of smell (anosmia) or a reduced sense of smell (hyposmia) is fairly common (L.J. Myers, Auburn University, pers. Commun.) Various sources list parasites, poor diets, fatigue and age as contributing factors to reduced scenting ability. Take good care of your dog and he’ll reward you with superior work in the field.
In Part 1 of this series, we stated “…one day your dog is pointing birds at 30 yards and the next day he can’t find a ham sandwich lying in front of his nose.” Your author hopes this three- part series has helped the reader now understand why this happens; and be more forgiving of your dog.
Literature Cited
Coren, Stanley,
Hodgson, Sarah, 2007, Understanding A Dog’s Sense of Smell
Dahlgren, David
K., 2012, Use of Dogs in Wildlife
Research and Management, Utah State University
Holloway 1961
Myers, L.J., 1988,
Auburn University
Syrotuck, William G.,
1972, Scent and the Scenting Dog
Tyson, Peter, 2012,
Dog’s Dazzling Sense of smell, NOVA ScienceNOW
Paul Fuller is a life-long sportsman. He’s been an outdoor writer since 1971. He’s the host and producer of the award winning Bird Dogs Afield TV show (www.birddogsafield.com) and produced the epic video Grouse, Guns & Dogs. Paul shot over his first German shorthaired pointer in 1961. Paul may be reached at paul@birddogsafield.com.
Copyright 2017, Paul Fuller.
