Understanding Bird Scent -- Part 3: The Dog's Nose

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.

Understanding Bird Scent -- Part 2: Diffusion

In last month’s column, Understanding Bird Scent-Part 1…The Bird, we learned about how bird scent is created.  We know that there are scent rafts that create four different scent clouds that carry the scent into the atmosphere.  Once the scent is airborne, there are numerous atmospheric weather conditions that affect the scent dispersal and the ability of our pointing dogs to locate a bird. In this part, of our three part series, let’s examine those weather conditions that affect bird scent diffusion. We’ll also look at the effect weather has on bird movement which also produces scent diffusion.

First, however, let’s get the scent off the bird.  Every warm living creature has natural body air currents.  Warm air rises so the body air current of a bird goes from the bottom to the top of the bird.  Those body air currents transport the scent rafts, and resulting cloud, up and into the atmosphere.  That’s why we want our pointing dogs to carry their heads high…that’s where pointing scent is most concentrated.  And, as we go through this three part series, it’s important to understand that the most common method used for quantifying scent is scent concentration.

Now that our scent rafts are airborne, they are impacted by weather.  And, this is where it can become rather confusing…for both the dog and the hunter.  When one considers the variations of temperature, atmospheric pressure, and humidity from hour to hour through a 24 hour period, it can be compared to commuting between the tropics and the arctic in one day.  (Scent and the Scenting Dog, William G. Syrotuck 1972).

As difficult as it may appear, let’s analyze  weather conditions that affect scent and see what we can learn. We’ll look at air currents, wind, temperature, humidity, barometric pressure and the moon phases.

Let’s begin with the simplest: air currents in hilly or mountainous areas and  not influenced by wind.  As the sun rises and heats the ridges, air currents travel up the mountain.  This process is often referred to as an up-draft.  As the sun gets higher, the lower elevation becomes warm and the air current continues upward. At about 3:00 pm in the afternoon, a reversal begins.  The sun is lower in the sky and the ridges of the hills begin to cool.  This cool air runs down-hill.  With other factors being somewhat neutral, that means we start our hunt in the morning at the top of the hill or mountain and work our way down.  In the afternoon, as the air current reverses, we start our hunt at the bottom of the hill and work-up.  The resultant turbulence (the changeover beginning at about 3:00 pm) causes a specific layer two to three feet above the ground.  Rafts which fall into this layer will be kept airborne at the height of two to three feet for long distances.  This effect is relatively short lived, usually one hour or less. (Syrotuck 1972).  This tells us that the rafts (see part 1) carrying the scent in the scent cloud may be most detectable between 3:00 and 4:00 in the afternoon; which coincides with feeding activity which means a moving bird and more scent dispersal. All are positive conditions for a pointing dog.

Now, we’ll discuss wind (airflow). How wind affects scent can be a complete article itself. And, in How Scent and Airflow Works, Jennifer Pennington did just that.  Pennington, along with many others, suggests that a great way to see how wind can affect scent is to watch smoke. We’ve all sat by a camp fire and experienced how smoke shifts from one direction to another.  One minute we have smoke in our face so we move to the other side of the fire…and then very quickly the wind changes and we have smoke in our face again.  Wind is a tough hombre to pin down.

After diffusion from the bird,  Pennington identifies fourteen different types of airflow (wind) that can affect how scent is carried through the atmosphere.  Her document is ten pages so for our research, we’ll cover the basics.  We’ll begin with the Latimer Flow which is a straight flow off the bird.  There are no obstacles to block the air flow or significant wind to change the direction.  On a calm day, this might be what we would experience in large open fields found in the prairies.  For those of us who have hunted the prairies, we’ve all experienced those 100’ points in perfect weather conditions.

Next, we have turbulent airflow.  If the prevailing breeze hits an object such as a building (of any size), a pile of brush, large granite rocks (like what we find in New England), the flow (and scent being carried) tumbles over the obstacle and becomes turbulent on the opposite side.  That turbulence creates a very unorganized jumble of scent which tumbles around and would be difficult for a pointing dog to pick-up at any distance. 

Pennington’s next airflow is a coning plume.  This is most likely where the term “scent cone” originated.  Scent travels from a very narrow and dense concentration to a broader cone configuration. With a good breeze, the scent can travel a great distance.  Pennington states that this is ideal scent dispersion for dogs. 

Those three airflow (wind) types cover most of the situations the pointing dog owners will encounter.  A simple rule for the pointing dog owner/hunter is that airflow (wind), and the scent that is being carried, always follows a path of least resistance.  And the old simple rule of hunting into the wind remains valid. We’ll finish wind with the following:  Strong wind may disperse rafts and scent to the point where they cannot be detected, whereas little or no wind may limit the area over which they are transported. (Geiger 1965)

Now let’s look at temperature and humidity.  Scent creating bacteria needs moisture and warmth to grow and stay alive.  Without those two factors, bacteria (and scent) will die. Bacteria are 80% water. Very hot and dry atmospheres dry up the nutrients of the bacteria to the point where activity will cease. (Syrotuck 1972) Extended warm temperatures with no moisture will eventually lead to scentless birds.  My wife and I were hunting Manitoba several years ago.  It was so dry that when you put your foot down the vegetation crunched like rice crispies (pop, snap & crackle).  Vegetation was dead and creeks were dried up.  Our dogs, with very good noses, ran over the few birds we found.  Your author has a very good friend who has a 27,000 acre quail ranch in Kansas.  In November of 2016, they went 60 days without rain.  His dogs had the same issue…the birds had no scent.  Remember that uropygeal gland we discussed in Part 1?  With no water, that gland most likely becomes much drier and disperses less, if any, scent.   

Because there are so many variables, it’s hard to find research that provides perfect temperature and humidity levels for a scenting dog.  One short paper I discovered suggests that both a humidity reading and a temperature (Fahrenheit) between 40 and 60 is ideal.  Those levels provide enough warmth and humidity (moisture) for bacteria to grow and both provide a level of comfort for the hunter and dog.  Also, if the temperature and relative humidity levels are approximately the same, there will be dew on the ground in the morning.  The dew revitalizes bacteria that has fallen to the ground…and that creates stronger scent. How about freezing temperatures? Freezing or near-freezing temperatures retard bacterial action, extending the decay period but reducing decay rate. (Syrotuck 1972) 

Barometric pressure and wind have been used to predict fish and game activity for decades.  We’ve all heard the old adage many times:  Wind in the East, fish bite least, Wind in the West, fish bite best, When the wind is in the North, The prudent angler goes not forth, When the wind is in the South, It blows the hook in the fish’s mouth.  Although this old predictor talks about fishing, it also applies to game movement…and that includes upland birds.  John Alden Knight, Moon up – Moon down  (1972) explains this old angler’s guideline as follows:  Wind in the East-harbinger of a falling glass (barometer) and bad weather along our Atlantic seaboard.  The fish (and game) take to cover and are not interested in food for the time being. Wind in the West – good weather with a fresh breeze and a high or rising glass, probably indicating good fishing (and game movement). Wind in the South – warm, gentle breezes and good weather, with a steady barometer.  No wonder the fish (and game) go on the feed. Wind in the North- as a rule this is a strong, cold wind, shifting to the east.  That means adverse temperatures and a falling glass.  Obviously bad weather for fishing (or hunting).  Knight goes onto say that the effects of the barometer on fish and game movement had been proven beyond doubt.

The average sea-level barometer reading is 29.92.  Knight points out that as little as one one-hundredth of an inch downward in the barometer can shut off fish and game movement.  So, a higher barometric pressure promotes more game movement and with the high barometric pressure pushing downward, there is more scent concentration for our dogs.

One more offering from Knight’s Moon up-Moon down.  Knight feels that game move more during a high moon.  This fall, check your moon calendar and see if you feel more birds were located during a high moon.

Your author hopes readers have learned something about scent diffusion that helps make your next hunting season more successful.  The bottom line on when to go hunting….whenever you can.  Part 3 of this series will discuss the receptor of all this scent …the dog’s nose.

Literature Cited

Geiger, R.  1965, The climate near the ground.  Harvard Univ. Press, Cambridge, MA

Knight, John Alden, 1972, Moon up-Moon down, Solunar Sales Co.

Pennington, Jennifer, 2016, How Scent and Airflow Works, Virginia Search and Rescue Assoc.

Syrotuck, William G., 1972, Scent and the Scenting Dog

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.