A K9 Nose Work Conundrum: Is it Residual or Lingering Odor My Dog's Sniffing?

This week's post cites information from an article in Police K-9 magazine, which in part describes why scent terminology can be problematic for drug detection dogs. To see the article in its entirety, click here.



There is a key distinction between the work that drug or bomb sniffing dogs perform and the sport of K9 Nose Work we enjoy with our pet dogs, the key lies in how the two worlds define and place importance on what we call residual and lingering odor. According to the article in Police K-9 magazine, in the world of the police K-9, odor is odor regardless of the presence of 'source', or should I say regardless of the strength of the 'source'. If someone had a joint in his shorts three weeks ago, a drug sniffing dog might detect residual and/or lingering odor and alert on that guy's shorts! In the sport of K9 Nose Work we ask that the dogs find only the most concentrated source of the odor, and that they not alert to lingering odor - and try not to alert to residual odor (this can be challenging for reasons to be explained). So why is it that the professional sniffers get to alert to stinky gym shorts and our pet dogs have to parse a specific bloom from the scent bouquet? How do we help our dogs to become such scent sticklers? It might not surprise you to find out that our pet sniffers are capable of picking out a single pollen grain from that scent bouquet, all we need to do is give them a clear understanding of what we want from them in the search and fine tune it over time.

What do we mean by residual and lingering odor? Simply put, residual odor is some concentration of scent left behind after the removal of the source odor. Typically, this would occur when a scented cotton swab comes into direct contact with the environment as opposed to being contained in a tube or tin. Lingering odor is described as the fainter remains of scent in an area where source is no longer present. Where a dog might find a 'source' when residual odor is present, lingering odor is presumed to be much less concentrated and not resembling source odor for the dog. Lingering odor may be present without residual odor, but residual odor cannot be present without lingering (whatever more concentrated source left the residual odor also left lingering, and residual leaves its own, fainter lingering odor).

*Be careful not to contaminate your search areas with residual odor. A cotton swab dropped on the ground or stuck to a block wall is something the dogs can work through, but if the oil used to scent the swabs contacts any part of your search area, it should be removed and cleaned, and no searching should be done in that area until the highly concentrated oil has dried and the vapor has dissipated. Also important, never give your dog a reward and never use negative feedback if your dog gives a final response at a residual odor location. Just say, "okay, good dog", and move on. In most situations, we can be reasonably sure that the residual odor left after hide removal is not as strong as the hide itself, so the best course of action upon moving on is to have a sourceable hide for the dog to find and get rewarded for so learning and reinforcement can take place.

When a dog trained to find drugs or explosives does his job, he will find any amount of that substance or material he can - and in the case of explosives, we all want a dog who can find a subatomic particle's worth of bomb material to save lives and be better safe than sorry. When a dog trained to find birch, anise, or clove does his job, he will find the source of the hide. Birch, anise, and clove are not substances that put lives in the balance or break federal laws for possession (however, concentrated essential oils can be harmful, read product warnings and handling instructions before use). A K9 Nose Work dog can learn to process scent information - lingering and residual odor - and use it to reach the goal of finding source. This makes the activity & sport challenging and exciting; it's like marksmanship in the Olympics, a sniper in the field of battle may get the job done in whatever way necessary (and his is a serious job), but a marksman in a competition must use precision and meet a tighter standard (and his job is the exhibition of his skills).

Now that we can examine just what lingering and residual odor are and how they affect our dogs' performance in K9 Nose Work, how do we confront these challenges and get our dogs effectively using the scent information to find source?


Recognize the dog's earliest introduction to lingering and residual odor situations - dogs searching for primary reward (food or toy) will encounter lots of lingering and residual odor. Food grease leaves residual odor on boxes, food placed in a container and moved from one box to another leaves lingering odor. Take notice of how this is never a problem for the dogs. The main reason being that they know the ultimate reward in the search is the food or toy and there's no point hanging out where it was - only where it is. If you observe your dog as confronting these lingering and residual odor problems from the start, you should be less concerned about problems when you move to a target odor, like birch.


Allow the dog a chance to compare and make a right decision - Just like when we introduce food & toy (or critter) distractions, it's best to put the dog in the same vicinity as what you want him to ignore in favor of source odor - this way he actively chooses source odor over the distraction. With lingering & residual odor the choice is not to ignore their presence, but to use them as a marker on the path to source odor. When doing target odor searches, moving the hide just a few feet and letting the dog encounter lingering or residual odor in the presence of source odor will allow the dog to understand what pays. Keep in mind that we don't use some kind of rigorous process to prepare odor, nor do we use the same number of scented cotton swabs for every hide - it would be impossible to control the concentration of source odor for every hide. The dog does not have to make decisions regarding specific strengths of source odor in a search, he just has to choose the strongest concentration(s). If there are multiple hides, he works to find each one because they are all stronger sources than any lingering or residual odor. The hides can be different strengths, two cotton swabs and twelve cotton swabs, the dog will not ignore the two cotton swab hide because it's not as strong a source as the twelve cotton swab hide, he will treat them both as sources. And, over time, because he's consistently rewarded for source odor, when the dog reaches NW3 level skills and must clear a search area, lingering odor will not prompt him to give a final response unless the handler fails to read the dog and pushes him to search too long.


Keep your searches straightforward for the dog's learning - always make most of your training and practice searches straightforward such that the dog can build his understanding of what we want him to do for the game of K9 Nose Work. If we have him searching hides out of reach too often, we could be rewarding the dog for sniffing odor that is more like the lingering odor we don't want him to give an alert to - this usually happens because we handlers expect our dogs to give a final response in a certain area, but that might not be where the strongest concentration of odor is coming from. A search that allows the dog to puzzle through lingering odor and make a decision at source is more helpful than a search where he alerts at the base of a sign post to a hide that is 6 feet above him.



Teaching our dogs how to interpret lingering and residual odor is an ongoing process - we can add blowing/pooling odor to the list as well. Every search situation presents new challenges, and often the only way for our dogs to learn is to experience the search; we can't create a lab where we can teach them skills that will apply to real world searches, they just need to learn from the school of hard sniffs (with us, their chaperones on hand at all times to keep things from getting too hard).

I have some videos of the searches Muriel & I did at Nationals, so look out for a post in the coming weeks that shares those videos and tries to pull some teachable moments from them (shouldn't be too hard with the handling errors!)

Happy Sniffing!