The Importance of Scent to a Deer

Introduction

Throughout their evolutionary process deer have essentially developed as a prey species, and this is reflected in their body structure and physiological makeup. Their senses are highly tuned to give them the best chance of evasion and escape from harm.

Along with many other species throughout the world, deer rely heavily on their ability to scent (sense of smell) as a front-line defense mechanism allowing them to detect and identify predators often long before potential danger reaches them. As deer possess an inherent fear of predators, then their sense of smell is central to their survival.

To most animals, the airborne scent picked up by them undoubtedly generates a mental image probably as clear – if not clearer than a visual one. This allows them to assess the level of threat that may exist from the type of scent detected and its proximity through the concentration of scent in the air.

This article looks at deer scenting and to help increase your understanding of the important role that scent plays in the daily life of deer.

What is Scent?

Scent can be defined as an odorous substance containing pheromones.  A pheromone is a chemical substance produced by the deer and released into the environment.

When detected, these substances can initiate a physiological shift in the animal’s body through causing it to release a variety of hormones that can initiate either positive or negative psychological responses.

Ultimately these responses lead to a physical behavioural pattern. The precise nature of the pattern will vary dependent on the animal’s sub-conscious interpretation of the particular pheromone. For example, it may stimulate the animal to mate, or it may stimulate it to fight or run away.

Pheromones provide important ‘signals’ that can have a profound effect on other deer of its species, especially in their reproductive, territorial and defensive processes, but it can also be used by other species of animals – especially predators – to establish whether the animal qualifies as prey or not.

Scent is deposited by deer and many other mammals from a variety of scent glands on the surface of the body, but equally, it can be deposited in the urine or faeces, with the former typically deposited on prominent objects in an area such as shrubs, bushes trees, and even fence posts.

How is scent picked up and processed?

Scent is detected by the deer sniffing the air and picking up the scent by its olfactory receptors (also called smell receptors) in the nasal turbinates in the back of its nasal cavity.

The olfactory receptors are located on what are called olfactory receptor cells, of which there are millions – all capable of binding the molecules present in odour.

The olfactory cells form a layer of epithelium in the nasal cavity (Epithelium is a thin cellular tissue lining the external body surfaces as well as the surfaces of all internal organs and the surfaces of all body cavities)

In simple terms, each receptor cell has a single feeler-like structure, similar to antennae, half of which is buried in the cell, and the other half protrudes.

The external part (called cilia) is what detects the pheromone molecules and then transmits ‘messages’ to the cell and are in turn delivered to the brain via sensory nerves. The brain then initiates the release of hormones dependent on whether the ‘message’ indicates a threatening event, or a passive scent-related communication from another animal within the species.

 Just how Powerful is a Deer’s Sense of Smell?

This is, of course, difficult to quantify, but to put the question into context, the human with the most acute sense of smell in the world is far inferior to that of deer.

No doubt prehistoric man had a much more acute sense of smell in order to find prey, but throughout evolution, there has been progressively less need for humans to rely on the sense of smell as a means of detecting danger or finding food.

The average modern human has around 5 million olfactory receptors in their olfactory epithelium layer. In contrast, a dog has around 220 million olfactory receptors and a deer – whose very life depends on its ability to detect danger – has over 295 million olfactory receptors, allowing it to detect the scent of predators over a mile away in the right conditions, but certainly over several hundred metres.

Why do Deer lick their noses when Scenting?

It is important for a deer to maximise its scenting capability at all times.

For this reason it generally maintains a film of moisture over the external surfaces of the nose and especially the insides of the nostrils. This helps pheromone molecules ‘stick’ to the surfaces of the nose and nasal cavities.

Almost all deer will lick their nose many times per minute as an aid to this process.

What Information can be Passed on Through Scent?

Almost all Deer species, whether wild or domesticated, use scent to their advantage as a communicative medium.

When one of a group of wild deer detects the scent of a predator (including man), then pheromone output is dramatically increased producing strong chemical signals that are deposited from scent glands – especially the inter-digital and the sub-orbital glands – which saturate both the ground and the air around the deer.

As the animal runs, then scent is excreted onto the ground and into the air around them, acting as a warning to other members in the herd.

In Farmed Red deer handling, it can be clearly seen that when an animal becomes agitated or frightened, then the sub-orbital scent glands open up and produce a scent – to a human the scent resembles that of linseed oil.

This can lead to many other animals in the group becoming nervous, making handling more difficult. In such cases we would normally have a break from handling and give the remaining animals time to settle down, and for any lingering scent to clear before resuming the operation.

Scent glands also play an important role in the reproductive cycles of many female deer, helping to signal the onset of oestrus in the receptive hind/doe, a signal that can be detected from a considerable distance by a rutting stag/buck.

There are anecdotal accounts of Red stags that travel some considerable distances spanning many kilometres when they have detected the scent of ‘in-season’ hinds on the wind. Some have been known to cross wide expanses of water to seek out hinds in oestrus.

It is also known that Roe does will travel a considerable distance to bring a rutting Roebuck back to her own home range. This is almost certainly driven by scent where the female actually selects a buck to mate with.

Where are the Scent Glands?

All deer possess several scent glands throughout their body.

There are in fact two types of scent glands. These are SUDORIFEROUS glands and SEBACEOUS glands, and they and they are characterised by the particular type of secretions produced, and the mode by which the secretions are transferred to objects, plants etc.

Sudoriferous glands, such as the sub-orbital and inter-digital glands produce scent in conjunction with bacteria and other body secretions, as well as foreign particles to produce a unique chemical scent composition.

Sebaceous glands are usually associated with hair follicles and secrete and oily substance. Examples of Sebaceous glands are  the forehead and metatarsal glands. The hair on these glands are generally thicker, more robust and used to ‘brush’ the oily chemicals on plants and other objects.

Where are the Scent Glands Located?

The various scent glands are found in the following locations:

Inter-Digital – Between the hoof cleats of all four feet. Researchers discovered that in radio collared calves/fawns disturbed from cover whilst their mother is absent somehow know to stay within the home range of the female. It is believed that the home range may be denoted by scent from the inter-digital scent glands of the mother, but could equally be denoted by urine deposits.

In many species of deer, part of their territorial behavioural strategy relies on the habit of ‘scraping’ where the animal creates a depression in the ground with its front hooves. Pheromone production during this behaviour is almost certainly elevated as the scent from the interdigital glands is deposited both in the depression, and on the soil that it spreads around.

Forehead – On the forehead below the base of the pedicles is a patch of coarse hair beneath which are sebaceous scent glands that secrete a greasy substance. Scent is transferred onto plants and tree stems as the male animal frays during territorial marking and during the rut.

Sub-Orbital – Below the front corner of the eyes are sudoriferous scent glands in the form of relatively deep pockets or folds of skin containing dead skin cells, fluid, eye discharge as well as pheromone molecules. The sub-orbital gland is generally open when the deer becomes frightened or aggressive, but equally calves/fawns open up this gland when suckling, suggesting that this provides a communicative medium between the offspring and its mother.

Nasal – Situated just inside the nostrils, these glands are possibly responsible for secretion of chemicals during snorting, but cases of animals rubbing their noses on twigs (appearing to scratch) could well be a mode of scent marking from this gland.

Frontal – These are especially prominent in Muntjac, and again are opened when the animal becomes agitated, frightened or exhibiting mating behaviour. 

Penile – On the forward end of the penile sheath, surrounded by longer hairs are presumably activated when the animal urinates.

In Red deer especially – and no doubt in Sika too – the creation of wallows into which the deer will regularly urinate is undoubtedly an important source of pheromone distribution during the mating season. Presumably, females can detect this on the wind from many hundreds of metres away – maybe even longer.

Metatarsal – On the outside of the rear hocks. This gland is no doubt secreting chemicals as the animal walks through undergrowth, marking plant material as the animal walks along. However, during flight it is probable that this gland secrets a warning chemical which becomes airborne as the animal flees.

Inguinal – In the groin area between the rear legs. These are generally associated with Chinese Water Deer, which are believed to use the glands for marking reeds etc. and the animal walks forward and scent is secreted into the material as reeds pass between the back legs.

Caudal – Just below the tail in some species, this may be secreted when the animal defecates, but can also be airborne scent. This may well be the reason why Muntjac deer raise their tail as they flee from disturbance, as well as being a visual alarm to other deer. 

Do Deer Calves/Fawns have Scent?

As newly born deer are unable to run at sufficient speeds to escape danger, then their physiological defense strategy relies on both concealment (camouflage) and the fact that no scent is generated from them, and therefore they are unlikely to be detected by predators.

However, biologists believe that the mother possesses specialised olfactory receptors that allow them to locate their calf/fawn when it is disturbed and conceals itself in another location, however this is also effected through vocal communication between the mother and calf/fawn.

Deer Responses to Scent

In almost every event where deer are alerted to danger through scent, the animal will run to escape it, although in some circumstances deer may stand their ground, or even attack the predator – especially when they have a calf/fawn nearby.

In some species, especially the territorial species, where vocalised communications are largely ineffective, then chemical signals are used to aid communication in the species’ social structure.

This is especially useful in thick cover to denote territorial boundaries between both males and females, as the chemical signals can be active on physical objects for several hours.

The physiology of scent and its influence on behavioural patterns is an immensely complex subject, especially as Biologists have identified over 50 different compounds that form part of the chemical make-up of substances deposited from scent glands, especially in the forehead gland.

In view of this it is entirely possible that individual animals can be identified by others in their group, and possibly even that each animal has a unique chemical ‘fingerprint’ that helps identify it from all others.

Researchers have discovered that there is generally increased glandular activity on the forehead of older, more dominant males, and that such animals may scent plants and objects in their environment roughly twice as regularly as younger males of the same species.

How does Scent Relate to Stalker Success?

Stalker success is attributed to a range of skills and knowledge of deer behavioural patterns on the part of the stalker.

Whilst an understanding of deer scenting physiology can certainly influence stalker success, it cannot be relied upon as a sole means of predicting deer behaviour.  It can however help stalkers be in the right place at the right time, provided they are able to recognise deer territorial marking locations – A subject that will be dealt with in a future article.

In the USA much work has been carried out with the use of artificial and organic deer scents by hunters to attract animals, and therefore to aid culling of such animals especially during the rut.

Their effectiveness is difficult to quantify, but undoubtedly ranges from good to useless! Where it is believed to be good, there is a strong possibility that some other factor has influenced the deer to come within range of the hunter. There appears to be no conclusive evidence of its effectiveness as an attractant.

In the UK some stalkers have in the past used the full bladder from culled Roe bucks and does to ‘spray’ urine over the territorial marking locations, fraying stocks etc.

Anecdotal evidence suggests that the practice effectively caused Roebucks to demonstrate severe territorial behaviour at the site of such deposits, accompanied by much barking and aggressive fraying. Again no conclusive evidence exists to prove – or disprove its effectiveness.

As far as we are aware, there has been no scientific studies been carried out to establish whether or not the practice yields any sort of results, and it appears that the practice is not widely used in this country.

There may well be some question as to the ethics of using such techniques as a means of culling territorial bucks.