Published:  2015-04-19 Views:  1070
Author:  Fanie
Published in:  HartiesWatch
By Brig Strydom: How Do Tracker Dogs Track Scents?

The following article was presented by our own Brig Hannes Strydom on 27 March 2013 to the Hartbeespoort Technical Group. Presentations to this group are highly valuable by specialists in the field and a few of the presentations will be published on 

Brig. Strydom was head of SAP Vetinary Services and remains a strong pillar for the community regarding community policing. He was also the driver of the idea to establish an area SAP dog unit in Harties. SAP's decision to establish their specialised unit in Harties was solely due to Brig. Strydom's efforts while he was still in the Force. Unfortunately SAP made a curios U-Turn on the matter and their last indication was that they have reversed their decision and was looking at an alternative site for the area dog unit. Harties CPF has established a committee in this regard, where Brig Strydom is involved. Though, as with the CPF's working group on the new constitution, the authority / weight of their findings and future role of the K9 committee is not clear at this stage. 

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Enjoy the presentation:

Presented by
Director (Dr) JA Strydom
BVSc (Hons) MMedVet (Vet Eth)
SAPS Veterinary Service

⋆Due to a highly developed olfactory system,
dogs have a keen sense of smell
⋆ Dogs’ sense of smell have been exploited for
many years to trace missing persons, articles,
drugs and explosives
⋆ It receives its olfatory information from airborne
chemicals which activates receptors in its
nasal cavities

A dog can discriminate one human being’s
track from another, through imprinting
⋆At a later stage the dog can retrieve the
imprinted smell or odour for comparison and
⋆Through the process of imprinting and
retrieval, a dog can discriminate between two
or more odours


A dog has a complex nose design and a large
olfactory lob.

Theories on scenting ability
Track scent
⋆Damaged / crushed vegetation or disturbed
soil caused by a person, animal or object when
moving through the area
⋆This disturbed vegetation or soil at point of
contact, will have a different odour

Body odour
⋆When a person touches or handles an item he
imparts his scent to the article
⋆When a person walks through an area he
leaves his body odour on objects such as grass,
branches, etc

Air-borne scent
⋆ A person upwind can be detected by a dog’s
sense of smell through a person’s body odour
carried by moving air currents
⋆When a person moves through an area his
body odour is captured in ditches, potholes, tree
lines, etc from where the odour is released from
time to time

Raft scent
⋆The body casts off thousands of skin scales
(rafts) constantly. These rafts settle on the
ground or surface over which the individual has
⋆On these rafts we find living bacteria using the
raft for its nutrient value
⋆ The bacteria’s respiration can be described as
a vapour which has a very specific odour for
each individual

The nose is constantly made aware of numerous
odours in the environment. Several minutes after
exposure to a particular odour, humans, and
presumably the same occurs in dogs, become totally
unaware of the original odour and easily perceive
other odours, nearby. This ability is referred to as

⋆Highly volatile substances, eg petrol, xylene,
etc block the sense of smell for some time
⋆Certain medication and bad dental hygiene
also negatively effects a dog’s sense of smell
⋆Many substances considered odourless to
humans have an odour identifiable by dogs
⋆Certain breeds of dogs have a better sense of
smell than others

Why the difference?
⋆The nasal plane of working type of dogs have
well developed nose ligaments which widens
the nostrils during sniffing, enabling the dog to
draw in larger volumes of air
⋆Compared to humans, dogs have a much
larger nasal surface area due to the turbinates
in its nose. These tubinates slow down the air
movement, enhancing contact with the mucous
membranes covering the turbinates


The dog has a unique vomeronasal organ
which is a narrow tubular canal which starts
near the front of the nose and runs along the
floor of its nose. This organ has many olfactory
cells and hundreds of nerve bundles that
connect directly to the olfactory lobe.

Olfactory receptor cells are long and narrow with
filaments protrude out on the mucus layer. The
contact between the filaments and the odorous
substance is the critical factor.



The human body - a scent source
⋆The human body contains approximately 60
trillion cells, all with a definite life span
⋆ It is estimated that approximately 50 million
cells die in or on our body every second
⋆Skin scales (rafts) which are minutely small,
are constantly shed from our body
⋆Due to our genetic make-up, all four billion
humans on earth has an individual scent for
which a dog can discriminate.

⋆Due to our sweat and sebaceous gland content secreted
on the skin surface contribute to individual body odour
⋆ It is possible that:
⋆ Human scent is a result of skin bacteria living off the rafts
(shed skin scales)
⋆ The bacteria break down protein cell components and
secretions during their multiplication into amino acids
⋆ Amino acids are in turn broken down into ammonia,
methane and hydrogen sulfide -putrifaction
⋆ The result of the putrefaction process provides the
characteristic odours that the tracker dog follows



⋆Temperature variation has a pronounced
effect on bacterial activity and their release of
vapour gas
⋆Below optimum temperatures slow down
bacterial activity = less vapour production
⋆Above optimum temperatures destroys
bacterial activity which is the reason for the poor
scenting ability of a tracker dog on hot, dry days.

⋆Humidity also has a significant effect on
bacterial activity
⋆Humidity = moisture serves as a solvent for
food for the bacteria
⋆Early mornings dew is responsible for
increased bacterial activity resulting in improved
scenting ability in the early mornings.

Atmospheric influences and scent
⋆ The human body’s heat generates air currents
dispensing and introducing the bacteria laden
rafts into the environment
⋆Atmospheric wind, temperature and humidity
play an important role once the rafts have been
⋆The wind speed and direction will depend how
and where the rafts are dispersed eg, a cross
wind will result in a wide track.


Practical scenario
⋆A suspect breaks into a property on a hot and
dry midday and flees with stolen goods. The
rafts he leaves behind on his track dries up -
dehidrates, and bacterial activity decreases
⋆During the evening temperature drops and
dew falls. Due to drop in temperature bacterial
activity decreases further
⋆By early morning the rafts are again rehidrated
and temperature increases, re- activating
bacterial growth and vapour production.