WHAT IS SCENT DETECTION?
From the first domesticated dog, humans and dogs evolved together for a long time. Originally, dogs helped humans in tracking and hunting game. Depending on wind, dog can pickup scent plume 100 feet away and find the source (highest concentration of target odor). Group hunting was a selective advantage.
Scent detection canines identify a target scent against a complex, shifting background of odors. Canine olfaction surpasses human: dogs can detect parts per trillion. Even with our limited sense of olfaction, humans can detect scents at a distance, such as smoke of a fire burning in a room down the hall, breakfast from another floor, or cinnamon buns in a mall food court. Dogs smell even farther away. The main advantage with trained sniffer dogs is that they generally search larger areas faster, safer and cheaper than inspections by humans or chemical detecting robots. Learn more about scent detection disciplines at: https://nosework.huntersheart.com/about-2/what-is-scent-work-or-nosework/.
HOW DO DOGS SMELL?
For a 5-minute primer on canine olfaction, watch Ted-Ed’s “How do dogs “see” with their noses?” at https://www.facebook.com/TEDEducation/videos/2734615186551670/
SCENT CONES – HOW SCENT TRAVELS
When you hide scent inside a container, the scented cotton swab is the location of “source” Source is the highest concentration of scent, and we want the dog to find its precise location.
When there is no wind or air flow, scent disperses outwards equally, in all directions (unless it is blocked). To simplify, think of scent spreading out in the shape of an ice cream cone. This is known as a”scent cone”. In this figure of a scent cone being emitted by scent hidden inside a box with a hole, brighter green represents stronger odor and lighter green represents weaker odor. Humans can’t see that there’s a lot of scent building up inside the box, because it’s invisible, but it’s definitely there.
In wide-open, unobstructed areas, scent may travel hundreds of meters, where it can be detected by sniffer dogs.
DOGS COMPARE NOSTRILS
While searching for target odor, the dog’s nostrils dilate and he increases his sniffing rate so he can sample a larger volume of air. The dog’s left and right nostrils function independently. Mobile parts of his nose move and the shape of his nostrils is altered dynamically. When the dog is actively sampling, the inspired air travels dorsally, medially and ventrally around the obstructing alar fold. The right and left chambers of the nose are filled with scrolls of fine bone called turbinates aka conchae. Like toilet paper wrapped around a roll, this anatomical configuration maximizes the surface area available for olfactory receptors to interact with scent. When his left nostril detects more odor than his right, he adjusts his path more to the left. He alters his counter turning path, often bracketing back and forth as he tracks the scent cone back to its origin: source.
Aging (aka soak time) is the amount of time between placing scent in the environment and the time the sniffer dog starts searching. The longer the aging, the more widely the scent disperses into the environment. Imagine the green cone expanding, bigger and bigger. Experienced dogs can find hides aged for years, including outdoors with daily temperature changes and precipitation.
Note that scent must travel through gases (like the air) or liquids (like water) to reach the dog’s nose in order for it to be detectable. If there is no medium to travel through (like space or a truly pristine, airtight vessel), scent is not detectable. The tighter the seal of the container holding the hide, the longer you need to let it age so the scent cone can escape the container to be available in the environment. For example, if you place scent inside a container inside a car (which is tightly sealed to airtight, depending on the vehicle), it will take a long time for scent to be detectable outside the vehicle. This may take hours or days, depending on the scenario. If you practice various amounts of aging, from no aging up to weeks of aging in your scent detection training, your dog will be better prepared to handle a variety of real-life searches.
AIRFLOW & WIND
While visualising scent plumes is helpful for human understanding, it’s actually a simplification of the complex, changing environments dogs encounter in real life. In most search environments, there is wind, or at least smaller air currents. Wind and air currents move scent around, messing up the tidy scent cone. Outdoors, wind gusts may cause chaotic, erratic, unpredictable changes to the path scent travels, including swirling in circles and even changing or reversing direction mid-search! Scent is a moving target, and no two searches are identical.
Falling back on the foremost human sense of vision, picture how smoke from a bonfire dances upward in unpredictable shapes, dropping ash some distance from the fire when it’s windy. Those shapes are closer to how your dog “sees” scent patterns with his amazing nose, as he figures out complex puzzles.
Don’t worry: when you’re just starting to learn nosework in boxes indoors, you can usually just follow a trained sniffer dog as he finds source. But the more you understand how wind affects scent detection, the better you’ll be able to help your dog get to productive areas in more complex searches with wind, keep reading.
- For more detailed scent detection terminology, see our Glossary of Scent Detection and Nosework Terms
- Canine Olfaction Science and Law, Advances in Forensic Science, Medicine, Conservation, and Environmental Remediation, Ed. T. Jezierski et al, Taylor & Francis Group, Boca Raton, USA, 2016
- Tenhu, Hanna, and Terhi Helkala. Canine Scent Detection in Use of Locating Contaminated Sites in Finnish Defence Forces, downloaded from https://www.defmin.fi/files/2523/26_Tenhu_Hanna.pdf