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The Nose Knows

By: Michael DeLee

Humans have teamed with dogs for thousands of years to hunt for food; it's only natural that these days, we pair up in the search for contraband. Here's a primer on how a dog's nose works so you can explain it simply to a jury.

I recently met Jim McAllister, assistant district attorney for Fort Bend County in Richmond. Jim  prosecutes the county's drug cases. During our conversation, it became apparent that Jim was a somewhat frustrated prosecutor. His chief complaint about cases involving police service dogs and issues of probable cause and evidence recovery was the difficulty in explaining how a police service dog locates narcotics. Even though we all know that trained canines locate drugs by scent, the question is still, "How?" The answer is relatively simple; it is not magic nor mystery.
      

These days, much reliance-perhaps too much- is placed on mechanical devices to detect the signature odors of explosives in airports. A Massachusetts start-up company, for instance, is marketing a machine that can detect the presence of hydrocarbons leaking into the air in chemical plants and refineries. The scent receptors in this remarkable machine are nano tubes, the walls of which are 1 atom thick! The biggest downside to this technology is that the odor's source must be brought to the machine to be detected.
        

Only members of the animal kingdom can hunt and locate an odor's source, and in usefulness to man, the dog is at the top of the list. To explain how a detector dog can hunt and locate a scent's source, we must have an awareness of the three elements that enable the hunting process: canine anatomy; canine behavior; and scent mechanics.

Dog's nose vs. man's nose

Scientific study has conclusively proven that humans do not possess a sensory capability comparable to the canine olfactory sense. To appreciate the vast difference in olfactory ability between the two species, a comparison is necessary. If all the sensory epithelia in the average dog's nose were laid out flat, it would cover an area of about 450 square feet. Contained within this nasal tissue are more than 200 million scent receptors, some 15 million of which have infrared capability. That means a dog can literally smell heat.
      

If an average man's olfactory epithelia were laid out flat, it would cover about two square feet and contain less than five million scent receptors, none of which exhibit infrared capability. In the brain of the average dog, more than 12 percent of the cerebral tissue is devoted to processing olfactory information. In man, less than 1 percent of the brain is devoted to olfaction.

The Predatory Sequence

About 50 years ago, etiologists identified in both canids and felids an inherited sequence of behavior patterns. These patterns are predatory and function sequentially to insure the survival of the species. As a dog trainer, I call them the Predatory Sequence. This sequence is genetically hard-wired:  A dog must behave in accordance with the sequence's dictates. Activities that we humans term "dog training" are no more than modifying this inherited sequence. Essentially, these predatory motor patterns are a diagrammatic description of a wild canine or feline hunting prey. It looks like this:

orient>eye/stalk>chase/pounce>grabbite>killbite>dissect>consume

The Predatory Sequence, however, looks like this:

>orient > stalk > chase > bite > carry > dissect > consume

The symbol > signifies an initiator, or trigger stimulus, such as motion, odor, a command directive from a handler, a sound, or a number of other stimuli. The initiator has to occur for the hunting/detector animal to advance to the next phase.

Hunting coyotes (or lions, wolves, or bobcats) never eat within their hunting range. They always carry prey to a protected spot to feast to avoid sharing with pack members and to avoid larger or more numerous predators. Trainers universally modify the predator sequence at the "carry" phase.  Dogs, regardless of the task, are never allowed past that phase and rather are conditioned to bring their prey to man not carry it away from him.
           

Each phase of the Predatory Sequence is readily identifiable due to the dog's different behaviors while experiencing a particular phase. For example, while in the Stalk phase, a dog moves in short, halting, focused rushes, but in the Chase phase, the dog runs at break-neck speed and with reckless abandon.

Scent mechanics

The third element in the process is scent mechanics. Today, it is generally accepted by working dog trainers, such as those in the military, the Department of Defense, U.S. Customs, and police service, that scent emanates from a static location up and out in a conical configuration called a scent cone. The scent cone is distorted or influenced by heat, moisture, air currents, sunlight, shade, and topographical features. Well-trained, knowledgeable handlers use these influences to effect a successful hunt, like a quail hunter directing his pointer to quarter into the wind. Alternatively, if the scent's source, such as a pheasant, rabbit, or coon, moves, it leaves a trail. A trail, or track, can be easily imagined as a line of overlapping scent cones.
       

In either case, to understand how a dog can find hidden narcotics or anything else it's conditioned to locate, you must also understand six training concepts.

            [ ] A stimulus discriminative is information a dog receives through its senses. A Stimulus Discriminative could be a command directive, such as "find it," or it could be a peculiar odor such as the scent of cocaine.

            [ ] Odor is the detectable evidence of molecular migration from solids and liquids into the atmosphere.

            [ ] Absolute threshold is the minimum amount of a specific odor a dog can perceive. Absolute threshold varies from individual to individual such that each dog is his own benchmark.

            [ ] Just Noticeable Difference describes a dog's olfactory ability to detect minute differences in the concentration of a scent, both higher and lower concentrations.

            [ ] A negative indicator describes a dog's communication of where a scent is not.

            [ ] And, finally, the source is the precise location from which the scent cone emanates,
the point at which molecular migration occurs.

An example scenario

To demonstrate the interplay of how these five basic elements show how a dog's nose works during a hunt, here is a fictional scenario. Officer Jones and K9 Roscoe have been a team for some time. They have been successful because they consistently train to maintain their detection skills. Jones has devised the following training problem: He has located a flat, grassy field 600 yards long and 100 yards wide. In the center of this field and 100 yards from its far southern end he has placed a 16-inch plywood cube with holes drilled though four sides. Inside this cube is a zipper-locked sandwich bag containing 1/2 ounce of marijuana. A gentle 5-mph breeze is blowing from the south. Jones gets Roscoe out of the police car and walks him at heel to the center of the field on its northern edge and stops, facing into the breeze. This is to be a reconnaissance exercise.
        

Jones looks at Roscoe and asks, "Ready?" The word stimulates Roscoe, whose eager demeanor shows that the dog is excitedly focused. Jones points to his left front and gives the stimulus discriminative command directive, "Find it." Roscoe moves off to the southeast at an even  pace. Jones begins walking due south through the center of the field. The dog is sniffing the breeze on his right front and the ground he is covering. Roscoe's senses are focused. He knows if he follows Jones's directives he will eventually encounter an odor to chase. Roscoe is oriented.
       

As the dog nears the eastern edge of the field, Jones whistles and points to his right. Roscoe changes to a southwesterly course and examines the various scents on the ground and in the breeze. Near the western edge of the field, Jones whistles and points to his left and Roscoe takes another southeasterly course. This back and forth casting, or stalking, pattern continues until Jones and Roscoe have covered about 200 yards of the field. Suddenly, close to the field's eastern edge, Roscoe stops, puts his head high into the wind and sniffs intently, smacking his lips and licking his nose. Roscoe has found his absolute threshold for marijuana, and the scent triggers the dog to advance to the Chase phase of the Predatory Sequence.
        

Moving very quickly now, Roscoe heads again, without command directive, to the southwest. Now Roscoe is Chasing the Just Noticeable Difference of higher scent concentrations of marijuana on the wind. The scent concentration increases as the dog moves across the scent cone. When he is about 10 yards from the western edge, Roscoe stops and reverses his direction back to the southeast. He has just communicated to Jones, by negative indicator, where the scent is not, defining the edge of the scent cone on that side.
        

Moving much more quickly now, Roscoe changes his course to a south by southeast direction in pursuit of higher Just Noticeable Difference of concentration of the marijuana. Suddenly, about 25 yards from the eastern edge of the field, Roscoe wheels back to a south by southwest direction telling Jones, by negative indicator, that what they are hunting is not on that side either, defining the scent cone's edge on the east.
   

Roscoe is now moving almost due south and much more quickly than before. The quartering pattern has narrowed considerably, and he almost runs into the plywood cube and pounces upon it. Roscoe furiously paws the plywood box, in effect telling Jones, "This is it! Here is the source of the scent." Jones comes up behind the dog and throws a rolled up hand towel directly at his scratching paws. The sudden appearance of the flying towel triggers the impulse in Roscoe to Bite it. The dog shifts his grip, bites down harder, and begins to shake the towel, "killing" it. Jones tells the dog, "Good boy, Roscoe!", and holds out his hand. Roscoe carries the towel to Jones and delivers it to hand . The hunt is over, and that is how a dog's nose, knows.
 
Conclusion

Although the above-described scenario is ultimately simplistic, it serves well to explain how a "dumb" animal can do some remarkable detective work. The hunting process is an old one that man has employed for survival and enjoyment for many thousands of years. In all those years, the hunting process has not changed. Today's police service dogs hunt just like the ancients' wolves or dogs hunted. It is the interplay of anatomy, behavior, and scent mechanics that enable police service dogs to render such a valuable contribution to law enforcement.


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