Tracking refers to a dog's ability to detect, recognize and follow a specific scent. Possessing heightened olfactory abilities, dogs, especially scent hounds, are able to detect, track and locate the source of certain odours.Hepper, P. G., & Wells, D. L. (2005). How many footsteps do dogs need to determine the direction of an odour trail?. Chemical Senses, 30(4), 291–298. A deeper understanding of the physiological mechanisms and the phases involved in canine scent tracking has allowed humans to utilize this animal behaviour in a variety of professions. Through domestication and the human application of dog behaviour, different methods and influential factors on tracking ability have been discovered. While tracking was once considered a predatory technique of dogs in the wild, it has now become widely used by humans.
Physiological mechanisms
According to zoosemiotics animal communication involves an exchange of information between a sender and a receiver through a transfer of chemical signs. Described as representation and signification, a chemical sign can be produced without the presence of a dog and detected without the presence of the individual who produced it.Gadbois, S., & Reeve, C. (2014). Canine olfaction: scent, sign, and situation. In Domestic dog cognition and behavior (pp. 3–29). Springer, Berlin, Heidelberg. This means dogs have the ability to leave their own signs and detect previously laid signs without the presence of another dog or individual. It is this theory of zoosemitoics that explains how dogs are able to determine the direction of a seemingly invisible scent track.
Although dogs are capable of following both visual and olfactory cues, it appears that scent is their most effective source of information.Steen, J. B., & Wilsson, E. (1990). How do dogs determine the direction of tracks?. Acta Physiologica Scandinavica, 139(4), 531–534.Chicago Equipped with enhanced physical and neurological olfactory structures, dogs have a much more advanced sense of smell than humans.Weakley-Jones, B., & Rebmann, A. J. (2005). DOGS, USE IN POLICE INVESTIGATIONS. In Editor-in-Chief: Jason Payne-James (Ed.), Encyclopedia of forensic and legal medicine (pp. 221–223). Oxford: Elsevier. Specialized turbinate bones in the canine nasal cavity allow for increased exposure of chemical receptor cells to the air.Taslitz, A. E. (1990). Does the Cold Nose Know—The Unscientific Myth of the Dog Scent Lineup. Hastings LJ, 42, 15. This, paired with a proportionally large segment of brain devoted to olfaction processing, results in the enhanced smelling ability of canines.
Both physical and neurological attributes of dogs contribute to their ability to detect extremely small concentrations of specific scents and their ability to differentiate between odours. The accuracy of these detections is determined by the concept of scent groups. A scent group refers to a specific mixture of scents that comprise the overall odour of an individual. A dog's acuity to a scent group is so refined they are able to discriminate humans by odourSettle, R. H., Sommerville, B. A., McCormick, J., & Broom, D. M. (1994). Human scent matching using specially trained dogs. Animal Behaviour, 48(6), 1443–1448. and can even match certain scents to specific body parts of an individual.Berns, G. S., Brooks, A. M., & Spivak, M. (2015). Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors. Behavioural processes, 110, 37–46. Scent discrimination is most proficient while a human odour is fresh and becomes more difficult once an odour starts to fade.
Phases Tracking behaviour in dogs is exhibited through three separate phases.
Searching Phase
Initial period in which dogs attempt to find a track. Dogs sniff very quickly ten to twenty times between inhalations of breath.Thesen, A., Steen, J. B., & Doving, K. B. (1993). Behaviour of dogs during olfactory tracking. Journal of Experimental Biology, 180(1), 247–251. Sniff frequency is usually 6 Hz and occurs while the dog is in motion looking for a trail.
Deciding Phase
Track identification is apparent when the dog halts and then proceeds to take smaller step and the sniffing frequency of the dog becomes much longer. Period usually lasts 3–5s
Tracking Phase
Similar to the searching phase. Sniffing behaviour and walking behaviour become quicker.
Methods
Although dogs use physiological methods to detect scent trails, they apply these methods differently depending on the environments in which they are tracking. A scent results from the individual odour of a person being tracked or through an environmental disturbance odour that results from the physical movements of the person being tracked. The ways in which dogs track an individual, vegetative and track scent can vary depending on circumstances. Specifically, scent tracking ability of a dog depends on whether or not an individual deposits their scent in the air or on the ground.
An air scent is when human odours of sweat, cells, gland secretions, or toiletries circulate freely in the open air. The bacteria attached to fallen skin cells provide dogs with odorous by-products that enhance the individuality of a trail. While an initial air scent is much stronger than a ground scent, a ground scent remains detectable for a longer period of time.
A ground scent is the combined permeations of trampled vegetation, bugs, mud, and soil disturbed by an individual's footprints. The disturbed soil releases moisture and kills plant life which results in a different odorous by-product. Each footprint releases a new odour more potent than the ones of the undisturbed vegetation surrounding it.
A track scent is often a mixture of both the air scent and the ground scent being left behind by an individual. Dogs are able to determine a track scent by identifying a combination of both human odours and environmental odours released by an individual. They then use the strength of this overall scent to determine the directionality of a trail and track along that route. Since an initial footstep is much less potent than the last footstep taken by an individual, dogs move in the direction where the scent seems to become stronger. Additionally, dogs have been observed to alternate between visual tracking and scent tracking depending on the circumstances of their environment. For the most part dogs prefer to use olfactory cues even when the target or visual cues are within their line of sight.Gazit, I., & Terkel, J. (2003). Domination of olfaction over vision in explosives detection by dogs. Applied Animal Behaviour Science, 82(1), 65–73. However, there has been research conducted where dogs have been shown to rely on visual, social or cognitive cues to identify the tracks of an individual.Dumas, C. (1998). Figurative and spatial information and search behavior in dogs (Canis familiaris). Behavioural Processes, 42(2–3), 101–106.
Factors that influence tracking ability
There are many different factors which influence a dog's ability to successfully determine the directionality of a track. The age, sex, and even personalitySvartberg, K. (2002). Shyness–boldness predicts performance in working dogs. Applied Animal Behaviour Science, 79(2), 157–174. of a dog can greatly influence tracking behaviour. Male dogs have been said to more accurately determine the direction of a trail than female dogs. It is hypothesized that this is due to the evolutionary history of male dogs. Male olfactory ability of canines is superior to that of females because historically it was their duty to find mates and mark territory. Canine olfactory sensitivity is also found to diminish, therefore younger dogs tend to have superior tracking to that of older dogs. Personality traits of dogs affect both their ability to be successfully trained and their ability to successfully track. Dogs that are more active and confident tend to perform better during training activities and tracking activities.
The mannerisms of the handler working with the dog can also affect tracking ability. It has been discovered that humans and animals share very specific social skills that enable them to bond and work together effectively.Miklósi, Á., & Topál, J. (2013). What does it take to become ‘best friends’? Evolutionary changes in canine social competence. Trends in cognitive sciences, 17(6), 287–294 Adaptations of social tolerance and attentiveness has enabled dogs to participate in cooperative problem solving with their human counterparts.Ostojić, L., & Clayton, N. S. (2014). Behavioural coordination of dogs in a cooperative problem-solving task with a conspecific and a human partner. Animal cognition, 17(2), 445–459. Social attentiveness refers to an animal's ability to pay attention to their partner's actions and behave accordingly.Range, F., & Virányi, Z. (2015). Tracking the evolutionary origins of dog-human cooperation: the “Canine Cooperation Hypothesis”. Frontiers in psychology, 5, 1582. It is this factor that explains how dogs are capable of interpreting and reacting to cues from their handler. Pointing, gaze shifting, and facial expressions demonstrated by the handler can be used by the canine to locate objects and follow a certain direction. Canines are even able to interpret the unconscious signals of the humans they work with. Therefore, handlers are trained to be cautious of their actions in order to ensure their demands are being properly perceived by the dog.
Human uses of tracking dogs
Human uses for tracking dogs are dependent on many different factors. Specifically, the demands of a job often influence which kind of dog humans choose to train and employ. There are three different types of scenting dogs based on their affinity for air scents, ground scents and tracking scents. Categorized as tracking dogs, trailing dogs, and point source dogs, each one specializes in a different method of tracking.
Tracking dogs Tracking dogs are known for their ability to detect and follow the vegetative vapours released from disturbances of plant life. They stay very close to foot paths and are able to follow considerably aged tracks.
Trailing dogs Trailing dogs have a stronger affiliation for proponents of human scent near the trail they are tracking. They can be observed deviating slightly from or crossing over the trail they are tracking. Trailing dogs heavily rely on scent because the trails they follow often do not have any visual cues for tracking. Tracking and trailing dogs are often used interchangeably for police aid in human, suspect and victim searches.
Point source dogs
Point source dogs are specialized in air scent tracking and tend to ignore ground scents. They utilize increasing intensity of specific odours to identify and track a trail to a certain target object. There are two separate classifications of point source dogs: detector dogs and discrimination dogs. Detection dogs are most often used to identify both non-biological and biological scents of a target object while ignoring other non-target environmental scents.Browne, C., Stafford, K., & Fordham, R. (2006). The use of scent-detection dogs. Irish Veterinary Journal, 59(2), 97. Discrimination dogs are most often employed by police forces to identify the scent of a specific individual being tracked. This differs from detection dogs because they are required to react to a scent that matches or differentiates between other ones instead of identifying that a certain scent is present.
Specific uses of detection dogs
Explosive and mine identification Bacteria detection in buildings and homesKauhanen, E., Harri, M., Nevalainen, A., & Nevalainen, T. (2002). Validity of detection of microbial growth in buildings by trained dogs. Environment international, 28(3), 153–157.