Types of Scent Discrimination Dogs

A scent discrimination dog is trained to follow and/or identify the scent of an individual person or animal.  These dogs are described as scent-specific.  In most cases the search dog handler first provides the dog with a scent article containing the the scent of a specific person or animal.  Scent-discrimination dogs may work in one of several ways.

Trailing Dogs

A trailing dog is provided with a scent article (such as from a missing person or animal) and follows the strongest scent trail left by that individual.  Due to the behavior of scent, the scent trail may not be located where the individual actually walked.

Tracking Dogs

Many people use the terms tracking dog and trailing dog interchangeably, but there is technically a difference.  A tracking dog will focus on crushed vegetation and ground disturbance along with deposited scent in order to follow in the exact footsteps of the suspect or missing person.  Some tracking dogs are not scent-specific and just follow human scent and ground disturbance.  Tracking dogs may be used by the police, but most tracking is recreational such as AKC Tracking.

Scent-Specific Area Search Dogs

Though not common, some scent discrimination dogs may not be trained to track or trail at all.  These dogs are trained to only search for air scent coming directly off of the missing person or animal.  A scent-specific area search dog will only search within an area determined by the handler.

Scent Matching or Scent Lineup

Most scent discrimination dogs should also be able to perform scent matching or a scent lineup.  In a scent lineup, the search dog is tasked to match the target scent to one or more scent samples.  For example a police dog may match a scent article from a crime scene with a lineup including a suspect.  Or a conservation dog may pick out all the scat samples belonging to an individual animal.

Scent Discrimination Dog Research Studies

The lack of scientific research on scent discrimination dogs is really surprising given that search dog evidence is admissible in court in many locations (Brisbin 2000).  Most scent discrimination experiments focus on scent matching or lineups rather than trailing.  Studies of scent discrimination dog accuracy may measure one or more factors:

• Sensitivity: this measures how often the dog detected the target scent when it was present.  A dog with poor sensitivity will miss more correct matches.  They might also fail to find a scent trail when one is present or lose a scent trail they were following.
• Specificity: this measures how often the dog correctly identified or matched the scent article to the target(s).  A dog with lower specificity with have more frequent false alerts.  They might follow the wrong trail or alert on the wrong person.

Human Scent Lineup Studies

In these studies, scent discrimination dogs were presented with a sample of individual human scent and tasked to find matching samples from a series of scent samples or an actual lineup of individuals.  Settle et al. (1994) found that 7 police dogs showed an 80% accuracy in matching scent samples after 9 months of training.

Schoon (2001) reviewed methods of scent identification lineups in the Netherlands .  A prior study by Schoon (1998) determined that scent lineups were similar in reliability to bloodstain, tool marks and hair analysis (i.e. moderate reliability).  However, using the revised protocol, he concluded that the scent lineup should be considered as reliable as fingerprint, firearms and footwear analysis (i.e. highest reliability).  Part of the revised protocol involved disqualifying dogs that failed test lineups prior to being given the scent article from the crime scene.  To qualify as accurate, the dog also had to correctly match the suspect’s scent in two successive lineups.

Marchal et al. (2016) described the type of rigorous training that is involved in developing a highly accurate scent discrimination dog.  These dogs were trained for use in judicial case lineups in France.  Dogs that completed this program showed an 85% sensitivity (i.e. only 15% missed matches) and 100% specificity (zero false matches).  The initial training program took 10 months (with training sessions 5 days per week) followed by continuous training for 8-10 months.  Table 1 shows the improvement in accuracy over ten periods of continuous training.  Near the end of that program, only dogs that gave no false alarms over 200 trials entered into the judicial case program.  Dogs continued to receive training throughout their working life.  Even with all this training, they did not rely on the accuracy of a single dog.  In a judicial case task, scent-matches were always confirmed by 2 to 7 other dogs working on the same case.  The number of lineups used per court case averaged 14-39 with 4.6 to 13 lineups per dog.

As an interesting side note, Marchal et al. (2016) found that (9) German Shepherds outperformed (4) Belgian Shepherds (Malinois).  The German Shepherds showed higher sensitivity and zero false alerts.  They suggest that the Belgian Shepherds exhibited a decreased level of attention in completing the scent lineups.

Wildlife Scat Matching Studies

In these studies, scent discrimination dogs were presented with the scat sample of an individual animal and tasked to find all matching samples from a collection of other scat samples.  This information can be used to better estimate populations of wildlife using scat collections.

Kerley and Salkina (2007) tested the ability of 5 dogs to match 58 Amur tiger scats to 25 known tigers.  They found that the dogs correctly matched scats 87% of the time.  The accuracy of four out of five dogs increased to 98% with repeated-trial tests.

Wasser et al. (2009) found that 3 dogs correctly matched maned wolf scat samples to the correct individual 79% of the time while missing 21% of scats (averaged from their Table 1).  On average, the dogs selected the wrong match only 9% of the time except for two samples that they got wrong 75% of the time.  They speculate that there may have been cross contamination of those samples.  For accurate results, the researchers recommend using 3 scent discrimination dogs and only using results where at least 2 out of 3 dogs selected the same sample matches.

Scent Trailing Studies

I did a lot of searching, but I was only able to find a few research articles on the accuracy of scent trailing dogs.  Only the first study (Harvey and Harvey 2003) tested dogs on longer, aged trails.  The other studies used short, fresh trails.

Harvey and Harvey (2003) conducted the first published research study on the trailing ability of the bloodhound.  Eight bloodhounds were selected that had all started their training prior to six months of age.  They were divided into two groups based on their experience.  Novice dogs had less than 18 months of training experience.  Veteran dogs had more than 18 months training and had run one or more trails for law enforcement or search and rescue.  Five trails were set by pairs of people and included a split trail near the end.  Trails were 0.5-1.5 miles long and set in variable terrain in areas with lots of foot traffic.  All trails were aged for 48 hours and their location was unknown to the trailing dog handlers (i.e. blind trails).  Overall, novice dogs only had a 53.3% find rate and one false identification.  Veteran dogs had a 96% overall find rate with no false identifications.

Stockham et al. (2004b) studied whether bloodhounds could use scent from detonated pipe bombs and arson devices to successfully track and identify a target individual.  Twenty bloodhound-handler teams participated in the study.  Trails were set in an urban public park using a split trail method.  Test trails were only 32-41 meters long and were not aged.  Overall, the dogs correctly identified the target person in 53 of the 80 (66.3%) bomb-debris experiments and 31 of the 40 (77.5%) arson-debris experiments with no false-positive identifications.  Bloodhounds with more case experience had a higher success of finding a scent trail and identifying the subject, but no statistical analysis was conducted.

Harvey et al. (2006) tested the ability of 9-13 bloodhounds to distinguish between monozygotic twins, related people and unrelated people that lived together versus those that lived apart.  Scent trails were all on grass, only 150-200 meters long and aged less than 60 minutes.  Two tests were run: Test 1 looked at negative trails, and Test 2 was a split trail.  Table 2 shows the percent of bloodhounds that performed better than chance in trailing and identifying individuals from the split trail test.  Most dogs struggled to differentiate between twins, but had moderate to high success for related people and non-related people, especially when living apart.  The researchers conclude that the results suggest that “the discriminatory capabilities of the bloodhound seem to greatly depend upon a person’s genetically derived odortype.”  However, environmental odors may also be used to facilitate differentiation, especially when individuals are closely related.

Woidtke et al. (2018) conducted the most recent test on the accuracy of mantrailing (i.e. scent-specific trailing of a human subject).  Their study used 7 dogs from different breeds including 3 bloodhounds and one bloodhound mix.  Four dogs were mantrailing police dogs and 3 dogs were private search and rescue dogs.  The dogs had between 1.2-5 years of training/experience (mean = 3.4 years), and all were certified by their organizations.  All trails were set in urban locations with a T-junction at the end of the trail (i.e. split trail).  Trails were only 130 meters long and tests were conducted within 5 minutes of trails being set.  The dogs were marked as successful if they followed the correct scent trail or gave a proper “negative indication,” and they were marked as wrong if they followed the wrong trail (false positive) or could not find the trail (false negative).

This study found the following results:

• The success rate of the police dogs was significantly much better than the private search and rescue dogs (p=0.00001).
• Some dogs performed significantly better than other dogs on each test.
• The dogs were significantly more successful with (damp) saliva scent-articles than axillary (armpit) sweat (p=0.009965).

In about 25% of trials, the search dog was presented with a scent article from an individual that was not present.  In this case, the correct response is a “negative indication” – rather than starting to trail, the dog should indicate to the handler that no scent in present.  Police dogs gave correct negative indications 97% of the time versus 74% for private search and rescue dogs.  This difference in performance was also significantly different (p<0.01).

The researchers speculate that the police dogs performed better for the following reasons:

• They were all trained using a consistent method (Armin Schweda) for 2 1/2 years starting when they were puppies.
• They had several years of experience and received regular, weekly training.
• The handlers had many years of experience as police dog handlers.
• Three out of the 4 police dogs were bloodhounds.  This breed showed higher success rates overall.

Conclusions on Scent Discrimination Dog Accuracy

While dogs innately have amazing scenting capabilities, scent discrimination is a learned skill that takes years of practice to master.  Even well trained scent discrimination dogs are not infallible.  In the above research studies, some dogs were clearly better than others with accuracy ranging from around 53% up to 97%.  The most accurate dogs had received more than 18 months of initial training, had experience working real-world cases, and continued to receive regular, on-going training.  Search dogs with high accuracy still made mistakes between 3%-15% of the time.  For this reason, researchers recommended using 2 or more scent discrimination dogs to confirm the accuracy of scent-matches or lineups AND performing repeated trials with the same dog.  Novice dogs and those with less training made considerably more mistakes.  Accuracy rates for these dogs were around 50% to 75%.  That means that 25% to 50% of the time, these dogs might follow the wrong trail, lose the trail, miss a scent-match or identify the wrong individual or scent-match.  Overall, scent discrimination dogs appeared to make more errors related to sensitivity (i.e. not finding a scent that was present) than specificity (i.e. making a false or incorrect match).

Scent Discrimination Dog Success in Real-World Cases

The majority of these studies were done under laboratory conditions with only a fewer “real world” tests.  Of those tests, only one (Harvey and Harvey 2003) conducted tests using longer, aged trails, and those were only 48 hours old.  Most of the studies used specialized methods to provide the search dogs with uncontaminated scent articles (i.e. scent articles that only contained the target scent and not scents of other individuals).  Unfortunately, in real life most scent articles are contaminated with the scent of other people or animals.  This introduces another factor that could lead to more errors than were seen in the above research studies.  In order to work accurately with contaminated scent articles, trailing dogs must receive additional special training (Stockham et al. 2004a).

In police work, search and rescue, and lost pet searches, actual walk-up finds are very rare.  A walk-up find occurs when the search dog follows a scent trail and actually finds the missing person or animal or police suspect.  The likelihood of a walk-up find depends on many factors including species, age, circumstances of disappearance, environment, quality of the scent article, and age of the scent trail to name a few.  In many cases, a scent discrimination trailing dog may provide valuable information on where the missing person or animal traveled and/or where they are spending time, but other methods are usually used to locate the individual.  For more information on how lost pet search dogs work and when to use one see this article.

Literature Researched

Brisbin, I.L., S. Austad, and S.K. Jacobson.  2000.  Canine Detectives: the Nose Knows – Or Does It?  Science 290: 1093.

Harvey L.M., S.J. Harvey, M. Hom, A. Perna, and J. Salib. 2006.  The Use of Bloodhounds in Determining the Impact of Genetics and the Environment on the Expression of Human Odortype.  Journal of Forensic Science 51(5): 1109-1114.

Harvey L.M. and J.W. Harvey.  2003.  Reliability of Bloodhounds in Criminal Investigations.  Journal of Forensic Science 48(4): 5 pages.

Jones, P.  2006.  Scents and Sense-Ability.  Forensic Magazine April/May 2006.

Kerley, L.L. and G.P. Salkina.  2007.  Using Scent-Matching Dogs to Identify Individual Amur Tigers from Scats.  Journal of Wildlife Management 71(4): 1349-1356.

Marchal, S., O. Bregeras, D. Puaux, R. Gervais, and B. Ferry.  2016.  Rigorous Training of Dogs Leads to High Accuracy in Human Scent Matching-To-Sample Performance.  PLoS ONE 11(2): e0146963.doi:10.1371/journal.pone.0146963.

Settle, R.H., B.A. Somerville, J. McCormick, and D.M. Broom.  1994.  Human Scent Matching Using Specially Trained Dogs.  Animal Behavior 48(6): 1443-1448.

Schoon, G.A.A.  2001.  Scent Identification Line-Ups Using Trained Dogs in the Netherlands.  Problems of Forensic Science 47: 175-183.

Schoon. G.A.A. 1998.  A First Assessment of the Reliability of an Improved Scent Identification Line-Up. Journal of Forensic Science 43(1): 70-75.

Stockham, R.A., D.L. Slavin, and W. Kift.  2004a.  Specialized Use of Human Scent in Criminal Investigations.  Forensic Science Communications 6(3): 13 pages.

Stockham, R.A., D.L. Slavin, and W. Kift.  2004b.  Survivability of Human Scent.  Forensic Science Communications 6(4).

Taslitz, A.E.  1990.  Does the Cold Nose Know? The Unscientific Myth of the Scent Dog Lineup. Hastings Law Journal 42: 15-134.

Wasser, S.K., H. Smith, L. Madden.  N. Marks, and C. Wynne.  2009.  Scent Matching Dogs Determine Number of Unique Individuals From Scat.  Journal of Wildlife Management 73(7): 1233-1240.

Woidtke L, J. BreBler, and C. Babian.  2018.  Individual Human Scent as a Forensic Identifier Using Mantrailing.  Forensic Science International 282: 111-121.

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“The canine sense of smell is legendary and, as with many legends, it is sometimes hard to find the sources and separate scientific facts from urban legends”  – Goldblatt et al. (2009)

A well trained search dog should not make frequent mistakes, but how accurate are they?  How often do search dogs miss locating what they are trained to find?  How frequently do they make a mistake and indicate something is there when it is not?

There are several different types of search dogs including area detection, tracking and trailing dogs.  This article explores the scientific research on the accuracy of different types of area detection dogs.  This type of search dog is trained to search an area (determined by the handler) and indicate if they find one or more target scents.  Most area detection dogs are not trained to find the scent of a single individual (i.e. scent specific).  Dogs may be trained to find many different scents including humans (search and rescue dog), cats (cat detection dog), bombs (explosives detection dog), cancer (medical detection dogs), household pests (bed bug or termite detection dogs) or certain species of wildlife scat (conservation dog).

Scent Detection Dog Research Studies

Several research studies on search dog accuracy measured two factors: 1) how often did the search dog miss a target scent and 2) how often did the search dog misidentify a scent (i.e. give a false positive).  Helton (2009) reviewed the results of 12 different detection tasks including cancer detection, scat detection, termite detection and bomb detection.  He found that search dogs found and correctly identified the target scent 91.61% of the time (range = 75.00% to 100.00%).  Looked at another way, the search dogs missed indicating a target scent in an average of 8.39% of trials (range = 0% to 25%).  Helton (2009) also found that the search dogs gave false alarms (e.g. indicated a scent was present when it was not present) an average of 3.42% (range = 0% to 18.20%).

Additional studies conducted in the field provide more insight into the accuracy of search dogs.  Three field research studies (Harrison 2006, Long et al. 2007 and Smith et al. 2003) found that the search dogs located the correct species of wildlife scat 89% of the time (range = 72% to 100%).  While it is often difficult to determine how frequently search dogs missed locating scat in the field, Wasser et al. (2004) found that search dog handlers (rather than search dogs) located 0% to 25% of bear scat samples.  Reindle-Thompson et al. (2006) used search dogs to determine the presence of ferrets in prairie dog colonies.  One dog was 100% accurate at finding ferrets while the second dog only correctly indicated the presence of ferrets in four out of seven (57%) prairie dog colonies.

Possible Factors Affecting Scent Detection Dog Accuracy

As these studies indicate, the majority of detection dogs are accurate most of the time, but they are not infallible.  The training and experience of the search dog team (that is both the dog itself and the dog’s handler) are probably the biggest factors affecting how often a search dog makes mistakes.  Environmental factors can also have a strong influence on whether the search dogs misses locating a target scent such as a buried bomb or wildlife scat.  Some environmental factors that may make a search more challenging are hot dry air (Smith et al. 2003), gusty winds, lack of wind, and topography of the search area.  MacKay et al. (2008) estimated that scat detection dogs were able to locate a scat anywhere from 100 meters away to only 1 meter away depending on environmental conditions.

Still other factors that can influence a search dog’s accuracy are physical fitness and health (Altom et al. 2003 and Gillette 2004).  A hot or tired dog that is panting heavily is not able to sniff as effectively and fewer scent particles are detected.  Certain medications such as steroids (Ezeh et al. 1992) and some diseases can also effect a dog’s ability to identify and process scents (Furton and Myers 2001).

Accuracy versus Success Rates for Scent Detection Dogs

Whether or not the search dog is accurate is important, but that does not mean that they find their intended target 80 to 90% or more of the time.  In order to have a successful find, the target scent must be present in the search area, and the search area is determined by the search dog handler or another person.  Therefore, a large part of their success is determined by the knowledge and experience of the search dog handler, especially when finding lost people or lost cats.  In human search and rescue multiple search dog teams are often used and each is assigned a separate quadrant to search.  In lost cat searches, often a single dog is used to search the most likely areas where the cat will be found.  Typical success rates for cat detection dogs may be as high as 20% or as low as 5%.  In both human and lost cat searches, many other tools besides the search dog are also used to improve the chances of a successful find.

Recommended Reading

Helton, William, editor.  2009.  Canine Ergonomics: The Science of Working Dogs.  CRC Press.

Long, Robert, Paula MacKay, William Zielinksi, and Justina Ray, editors.  2008.  Noninvasive Survey Methods for Carnivores.  Island Press.

Literature Cited

Altom, E.K., G.M. Davenport, L.J. Myers, and K.A. Cummins.  2003.  Effect of dietary fat source and exercise on oderant-detecting ability of canine athletes.  Research in Veterinary Science 75: 149-155.

Brooks, S.E., F.M. Oi, and P.G. Koehler.  2003.  Ability of canine termite detectors to locate live termites and discriminate them from nontermite material.  Journal of Economic Entomology 96: 1259-1266.

Ezeh, P.I., L.J. Myers, L.A. Hanraham, R.J. Kemppainen, and K.A. Cummins.  1992.  Effect of steroids on the olfaction of dogs.  Physiology and Behavior 51: 1183-1187.

Furton, K.G. and L.J. Myers.  2001.  The scientific foundation and efficacy of the use of canines as chemical detectors for explosives.  Talanta 54: 487-500.

Gazit, I. and J. Terkel 2003.  Domination of olfaction over vision in explosives detection by dogs.  Applied Animal Behavior Science 82: 65-73.

Gazit, I, A. Goldblatt, and J. Terkel.  2005.  Formation of olfactory search image for explosives odours in sniffer dogs.  Ethology 111: 669-680.

Gillette, R.L. 2004.  Optimizing the scenting ability of the dog.  Athletic and Working Dog Newsletter, May.

Goldblatt, Allen, Irit Gazit, and Joseph Terkel.  2009.  Chapter 8 – Olfaction and Explosives Detector Dogs.  Canine Ergonomics: The Science of Working Dogs.  CRC Press.

Harrison, R.I. 2006.  A comparison of survey methods for detecting bobcats.  Wildlife Society Bulletin 34: 548-552.

Helton, William.  2009.  Chapter 5 – Overview of Scent Detection Work: Issues and Opportunities.  Canine Ergonomics: The Science of Working Dogs.  CRC Press.

Kauhanen, E., M. Harri, A. Nevalainen, and t. Nevalainen.  2002.  Validity of detection of microbial growth in buildings by trained dogs.  Environment Internationl 28: 153-157.

Kiddy, C.A., D.S. Mitchell, D.J. Bolt, and H.W. Hawk.  1978.  Detection of estrus-related odors in cows by trained dogs.  Biology of Reproduction 19: 389-395.

Long, R.A., T.M. Donovan, P. MacKay, W.J. Zielinski, and J.S. Buzas.  2007.  Effectiveness of scat detection dogs for detecting forest carnivores.  Journal of Wildlife Management 71: 2007-2017.

MacKay, P. D.A. Smith, R.A. Long and M Parker.  2008.  Chapter 7 – Scat Detection Dogs.  Noninvasive Survey Methods for Carnivores.  Island Press.

McCulloch, M. et al. 2006.  Diagnostic accuracy of canine scent detection in early- and late-stage lung and breast cancers.  Integrative Cancer Therapies 5: 30-39.

Pickel, D. et al.  2004.  Evidence of canine olfactory detection of melanoma.  Applied Animal Behavior Science 89: 107-116.

Reindl-Thompson, Sara A., John A. Shivik, Alice Whitelaw, Aimee Hurt, Kenneth F. Higgins.  2006.  Efficacy of Scent Dogs in Detecting Black-Footed Ferrets at a Reintroduction Site in South Dakota.  USDA National Wildlife Research Center – Staff Publications.  Paper 438.

Smith et al. 2003.  Detection and accuracy rates of dogs trained to find scats of San Joaquin kit foxes (Vulpes macrotis mutica).  Animal Conservation 6: 339-356.

Wasser, S.K., B. Davenport, E.R. Ramage, K.E. Hunt, M. Parker, C. Clarke, and G. Stenhouse.  2004.  Scat detection dogs in wildlife research and management: application to grizzly and black bears in the Yellowstone ecosystem, Alberta, Canada.  Canadian Journal of Zoology 82: 475-492.

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Dogs breeds commonly used in scent detection work include Labrador Retrievers, Bloodhounds, German Shepherds, Malinois, Beagles and several other hounds and spaniels.  These breeds have traditionally been used as hunting dogs, search and rescue dogs, police dogs and military dogs.  There is a common assumption (in part supported by their large number of scent receptors) that these breeds have a superior scenting ability.  On the other hand, short-nosed (brachycephalic) breeds like pugs, boxers, and bull dogs are often assumed to have a poorer sense of smell due to their squished faces and the reduced size of their rostrum.

Hall et al. (2015) set out to test the assumption that German Shepherds (a common scent detection dog) would outperform Pugs (a short-nosed breed) and Greyhounds (a sight hound) in a scent discrimination test.  

Study Methods

Hall et al. (2015) recruited pet dogs for the study that were in good health and had no prior scent training.  The subjects originally included 10 German Shepherds, 11 Pugs, and 10 Greyhounds.  However, 1 Pug and 9 of the Greyhounds refused to participate in the experiment.  The dogs were trained to alert to a cotton ball with anise oil buried in a bin of pine shavings.  In discrimination tests, the dog had to select the target odor that was in one of two bins.  They also ran the test using lower scent concentrations (10% and 1% dilution) of the anise extract.  For comparison to the scent tests, they ran a visual discrimination test using different size Styrofoam cups.

Results of the Study

Pugs performed significantly better German Shepherds in proportion correct (i.e. correct selection of the bin containing the target odor).  By the end of the testing, 9 out of 10 pugs had an 83% or greater accuracy compared to only 3 out of 10 German Shepherds.  (See Figure 2 from Hall et al. 2015)

Pugs also outperformed German Shepherds on the dilution tests.  The Pugs maintained a high level of accuracy at the 10% dilution, and the Pugs’ average performance at the 1% dilution was greater than the German Shepherds performance at the 10% dilution.  (See Figure 2 from Hall et al. 2015)

In the visual discrimination tests, Pugs and German Shepherds had similar accuracy.  (See Figure 4 from Hall et al. 2015)

Greyhounds were excluded from analyses due to the small sample size.

Conclusions

The results of this study did not support the hypothesis that a traditional scent dog (the German Shepherd) would outperform a short-nosed breed (the Pug) in a simple scent discrimination test.  In fact, Pugs outperformed German Shepherds even at low scent concentrations.  The researchers conclude that the differences “cannot easily be explained as general learning differences, general trainability, or simple motivational differences” because the two breeds performed similarly at the visual discrimination test.  Unfortunately, the Greyhounds could not be motivated to perform the test, so they were excluded.

Why might Pugs outperform German Shepherds?

Previous researchers have assumed that Pugs’ physical characteristics such as shrunken rostrums, crowding of the ethnoturbinate bones (see photos at the end of this article), and rotation of the olfactory lobe lead to reduced olfactory (scenting) ability (Roberts et al. 2010).  The results of this study do not support this assumption and further research is clearly needed.  Hall et al. (2016) suggest that Pugs may have a higher density of olfactory receptors which might counteract the effect of their shrunken rostrum.  German Shepherds have 225 million scent receptor cells, but I was unable to find any research relating to pugs (citation needed).  The placement of the olfactory recess may also play a role, but hasn’t been studied in Pugs.   Hall et al. (2016) also postulate that the difference in performance may be due to behavioral rather than physical differences.  For example, sniffing is thought to play a large role in olfactory perception and  “Pugs may engage in a superior sniff pattern.”

Does this mean that Pugs should be the new breed of choice for scent detection work?

Despite their performance in this particular test, in most cases Pugs would not make superior scent detection dogs because they are more prone to overheating and are not be able to perform the physical tasks of larger breeds.  Hall et al. (2015) are careful to point out that the results of this study should not be generalized to the larger population.  The German Shepherds in this study were pet dogs with no prior scent detection training while most German Shepherds used in serious scent work such as search & rescue, police and military are carefully selected from working lines of German Shepherds.  If Pugs were tested against these dogs, it is quite likely that the German Shepherds would outperform the Pugs.  Another study by Polgar et al. (2016) found that scent breeds performed better than non-scent breeds and short-nosed breeds in a natural detection task, but the difference was only statistically significant at the lowest level of concentration.

Literature Cited

Hall NJ, Glenn K, Smith DW, Wynne CDL.  2015.  Performance of Pugs, German Shepherds, and Greyhounds on an Odor-Discrimination Task.  Journal of Comparative Psychology 129: 237-246.

Polgar, Z, Kinnunem M, Ujvary D, Miklosi A, Gacsi M.  2016.  A Test of Canine Olfactory Capacity: Comparing Various Dog Breeds and Wolves in a Natural Detection Task.  PLoS ONE 11(5): e0154087.

Roberts T, McGreevy P, Valenzuela M.  2010.  Human Induced Rotation and Reorganization of the Brain of Domestic Dogs. PLoS ONE 5(7): e11946.

Resources

Learn more about dog scenting ability from the Canine Olfaction Lab at Texas Tech University.

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Many people with a lost pet think that a search dog is the best method for finding their pet.  However, most people tend to have unrealistic expectations and a lack of understanding of how a search dog works.  I previously wrote an article on considerations for Using a Search Dog, and in this series of articles, I plan to go more in-depth on how search dogs are used to search for different types of lost pets starting with lost outdoor-access cats, specifically those lost from their home.  An outdoor-access cat is defined as a cat that is allowed outside and unsupervised.  These are the most difficult type of lost pets to find because of the number of possible scenarios for their disappearance and due to the nature of their scent trails.

A Brief Overview of Scent & Types of Search Dogs

Our cats are constantly depositing scent wherever they go.  Scent theory describes scent as small rafts of skin (i.e. clusters of skin cells) that are constantly being shed from the body and that are then being broken down by bacteria (Syrotuck 2000).  Some scent is deposited with direct contact with the ground while additional scent flows off the top of the body through air currents and travels through the air before being deposited on the ground.  Scent will be stronger in areas where a cat repeatedly walks such as on preferred travel routes throughout their territory or where they rest.  Large concentrations of scent can also collect (i.e. scent pools) where a cat spends a period of time such as a sleeping spot or refuge such as under a porch.

There are several different types of search dogs that may be called by many different names: tracking dogs, trailing dogs, area detection dogs, air-scenting dogs, cat detection dogs or remains detection dogs to name a few.  Scent-specific dogs (generally tracking or trailing dogs) are trained to follow the individual odor of a missing person or animal.  This individual odor is composed of the skins rafts and personal bacteria of the individual and is catalyzed by body secretions of that individual (Syrotuck 2000).  Tracking dogs are trained to follow the scent left by the actual tracks of the missing animal, while trailing dogs are trained to follow the greatest concentration of scent on the ground.  Since scent is also deposited in air currents from the animal, this scent may travel several feet to over 100 feet from where the animal actually walked.  Although there is technically a difference between tracking and trailing dogs, they are often both referred to as “tracking dogs” by the general public.  For simplicity, I will also refer to tracks or trails interchangeably, but if you were to study scent theory, you would find that there can be a lot of variation between the two.  

Area detection dogs (e.g. air-scenting or cat detection dogs) are trained to search an area and locate the concentrated scent of any cat.  Ideally this scent is “air scent” coming off of the actual lost cat, but the dogs may also indicate on a scent pool such as under a deck where the cat hid for a while.  Both tracking/trailing dogs and area detection dogs are usually also trained to indicate on the scent of a deceased cat though some dogs are trained to specialize in just this task.  Most people tend to assume that a tracking/trailing dog is superior to an area detection dog, but once you understand the challenges of tracking a lost outdoor-access cat, you may find that this is not always the case.

Challenges of Tracking a Lost Outdoor-Access Cat that Disappears from His Home Range

Outdoor-access cats usually have a home range where they regularly travel and rest.  This may also be referred to as the cat’s territory or home range though technically it is only truly a territory if the cat defends it from other non-resident cats.  For more information on cat home range size, read this article.  The following illustrations show a very simplified version of a cat’s home range and movements.  The first series of pictures (Tracks 1-6) show a cat regularly traveling around his home range culminating in Track 7, which shows all his travels for that week.

If the cat then goes missing, you can now imagine how difficult it would be for a tracking or trailing dog to follow the scent trail of the missing cat.  A well trained dog can differentiate between an older and newer trail and direction of travel, but this is made more difficult with the many regularly traveled trails that will have an accumulation of scent and trails going in both directions.  

The difficulty of locating the lost cat is made more difficult if there isn’t an uncontaminated scent article.  The scent article is an item that smells like the missing cat that will be presented to the search dog.  This tells the search dog what scent trail to follow.  Many cat owners have more than one cat or dogs in the home, and it can be very difficult to find an item that is unique to the missing cat (i.e. uncontaminated from other pet scents).  If the scent article also contains scents of other cats/dogs that go outside, then the search dog may also follow the numerous additional trails left by these pets.  A well trained search dog will be trained in “missing member searches.”  This is where the search dog is presented with a contaminated scent article and is then allowed to smell all the other pets in the house, and determine which pet is missing.

How Different Probabilities Influence the Effectiveness of the Search Dog

When an outdoor-access cat goes missing from their home, there are different probability categories (or scenarios) for what might have happened to the lost cat.  These include: 1) Theft, 2) “Rescue” (i.e. when someone takes your cat because they think it is a stray), 3) Intentional Transport (e.g. a cat hating neighbor or angry ex-boyfriend kidnaps your cat and dumps him somewhere), 4) Unintentional Transport (e.g. your cat gets into the plumbers van), 5) Trapped (e.g. stuck in the neighbor’s shed), 6) Injury, Illness or Death (e.g. hiding because sick or injured or deceased due to illness or hit by car), 7) Wildlife Kill (i.e. victim of a predator attack), and 8) Displacement (e.g. chased out of their home range or otherwise leaves their home range). When an outdoor-access cat is lost away from home, this is a very different scenario and will be discussed in a future article.  In some search probabilities, specifically theft, rescue, or any type of transport, the tracking/trailing dog has no chance of successfully finding the lost cat because the cat has been removed by a person and there isn’t a scent trail to follow.  A search dog will also be unable to locate a cat outside if the cat is actually hiding or trapped inside the home, and this happens more frequently than people assume.

A tracking or trailing dog might be able to locate a missing cat within their home range (or just outside of it) if the cat is trapped somewhere outside, hiding and injured (such as from a severe cat fight or hit by a car) or deceased (such as hit by a car or killed by a predator).  An area detection dog can also be used to successfully locate a cat under most of these circumstances.  The picture below shows examples of where a cat might be located in each scenario.

Keep in mind that this is a very simplified scenario, and most cats will have a larger home range (usually 3 yards or more in each direction) which contains many more scent trails for the tracking/trailing dog to work through.  In neighborhoods where the houses are close together and fenced, a tracking/trailing dog will have a much more difficult time because he will be unable to follow the trails made by the cat since cats frequently climb under or over fences from yard to yard.  In these cases, an area search dog may be more effective to quickly check each yard for any sign of your cat.

Additional Challenges of Locating the Displaced Cat

One of the more common scenarios for a lost outdoor-access cat is that the cat has become displaced from his home range.  This may occur if he is new to the area and becomes lost or if he is scared out of his territory (such as by fireworks, construction, a loose dog, or another cat) and either becomes lost or is afraid to come back.  As much as we cat lover’s want to deny it, some “lost” cats will also choose to leave their homes when there is a significant change in the household such as a new baby, puppy or roommate.  Some cats are more sensitive than others and may leave due to a change in routine (such as a prolonged injury or illness of their owner) or even a small change in circumstances (such as a remodeled living room or change in brand of cat food).  In either case, the lost cat has left his home range and there may only be one scent trail leading to his new location.  The photo below shows an example of this scenario where the lost cat traveled to the neighbor’s home and got in a fight with their new cat and was chased across the busy road.

When a lost cat is displaced from their home range, it can be challenging for a tracking/trailing dog to work through all the scent trails and scent pools to find the one most recent track that leads away from their home.  This is made more difficult the longer the cat has been missing because the scent deposited throughout the home range might be an accumulation of years of scent while the trail leading out of the home range is only a single scent trail.  How long scent survives is a whole other discussion that I will blog about in a future article.  There has been some research that accumulated scent pools/trails may be viable for up to six months (Phillips 2006) while there is considerable debate on whether a single scent trail lasts for only 12 hours, a week or two, or even a month or more.  Personally I am skeptical of those who proclaim to track scents more than a month old.

If the search dog does successfully find the displaced cat’s scent trail, it is unlikely that they will actually locate the lost cat during the search.  These are referred to as “walk-up” finds and they usually only occur in less than 20% of searches and rates of only 5% or less are not uncommon.  Unless the lost cat is stationary (e.g. hiding, trapped, severely sick or injured or deceased), it is unlikely that the search dog will be able to find the exact location of the cat.  A cat that is being searched for by a dog will likely feel hunted and will evade the search dog team.  In fact, a well trained search dog team will likely stop the track for your lost cat if the search dog indicates that the scent is very fresh and the cat is likely nearby.  Using a search dog in this situation can provide some very useful information including where your cat went after leaving their home range and the area that they are currently hiding out.  This information can help you determine where to put up additional posters, distribute flyers, and perhaps set up a wildlife camera and/or humane trap.  Sadly, many people put all their hope (and often money) into hiring a tracking/trailing dog and then do not follow-up with the necessary search tactics after the search dog leaves.

Literature Cited

Jones, Phillip.  2006.  Scents and Sense-Ability.  Forensic Magazine (online edition).  April/May 2006.

Syrotuck, William G.  Scent and the Scenting Dog.  2000.  Barkleigh Productions, Inc.  Mechanicsville, PA.

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Missing Animal Response K9 Boot Camp

Presented by Kat Albrecht with K9 Pet Trackers 

Pet Detective Kat Albrecht is the founder of Missing Pet Partnership, the CEO of “K9 Pet Trackers,” and the author of the book “Dog Detectives: Train Your Dog to Find Lost Pets.” Since 1997, Kat has trained and certified many “MAR” (missing animal response) dogs and has trained over 200 “pet detectives” worldwide. Through her “MAR K9 Boot Camp” Kat evaluates and trains beginner through advanced dogs in K9 pet detective (MAR) work. This boot camp will be held over a 3-day period and consists of the following: Day 1 = evaluations (for dogs not already evaluated), sign offs for certification preparation, and private lessons Day 2 = lost cat search scenarios / lost dog search scenarios Day 3 = 30 minute private lesson with Kat. Students are encouraged to observe other handlers and dogs in training and also to work closely with training partners to help each other work on training assignments suggested by Kat. Both handlers and observers (without search dogs) are welcome.

This training is not yet scheduled, but it is planned for the spring or summer of 2015.  The cost for this 3-day training for “Handlers” with a search dog is $350.00 (cost for handler with 2 search dogs is  $550.00. Space is limited to just 15 participating handlers / dogs. Cost for “Observers” (without dogs) is $175.00 and there is no limit on observers.  For more information on the training, visit K9 Pet Trackers or email Kat Albrecht at info@katalbrecht.com.

I have attended this boot camp with my own search dog, Dante.  I would recommend attending whether or not you have a potential search dog yet, and I would be happy to answer any questions.   Just fill out a Contact Form.

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