Although deer utter little more than an occasional snort or rare bleat, they are remarkably communicative in ways that are difficult for humans to interpret. Visual and chemical signals work together to identify individuals, convey physiological or emotional state, and send specific messages. Collectively, these comprise expressive behaviour. Most of the current research on the chemical basis of deer behaviour is being conducted by Dr. Karl Miller at the Warnell School of Forest Resource, University of Georgia.

Olfactory communication

Deer communicate with a rich array of chemical signals or pheromones. As in most mammals, feces and particularly urine convey information on physiological state. Wapiti stags and other Old World deer wallow or spray urine forward on their bellies and manes during the rut. White-tailed deer and their New World relatives are unusual in that all genders and ages in all seasons routinely soak their hocks with urine adopting a distinctive urination posture.

Urine gives males their strong eye-watering rutting odour. As they stop feeding and mobilize fat, highly volatile ketones resulting from incomplete oxidation of fat appear in the urine. Odour therefore indicates quantitatively how hard the male is rutting and whether he is ‘spent’. The message may be significant to both females and other males.

Bucks show interest in urination of females particularly during the rut and follow their investigations with a lip curl (Flehmen). Although somewhat ritualized, the purpose of the lip curl is to expose the scent to the vomeronasal or Jacobson’s organ which assists the buck with his assessment of the doe’s reproductive stage and willingness to mate. The vomeronasal organ detects large non-volatile molecules. Because it has separate tracts to and stimulates different areas of the brain, it is properly considered the ‘sixth sense’.

The vomeronasal organ is found in cold as well as warm blooded animals but its function varies across species. Snakes use it in identifying prey and use their forked tongue to deliver the scent to the organ. In mammals, it serves a social function. The vomeronasal organ was once considered non-functional in humans but evidence is growing that it is involved in such phenomena as synchronization of menstrual cycles among women who live together. Humans like to believe they are too cerebral to fall prey to such base mechanisms. However, there probably is some truth in the phrase “the chemistry was right”. White-tails and mule deer have seven glandular areas which are used in communication. The tarsal gland is found on the inside of the hind legs at the hocks. (see fig. 2) Odors from this gland seem to help identify individuals and perhaps their gender and physiological status. Odor signatures are believed to be formed by a combination of skin secretions, urine and bacterial activity.

The metatarsal gland is found on the outside of the hind legs and appears like a white slit. (see fig. 2) It is particularly noticeable on mule deer and is greatly reduced in some South American whitetail subspecies. It is believed to release an ‘alarm’ pheromone to signal danger or at least anxiousness.

Interdigital glands are found between the toes and mark trails to allow deer to follow one another, a purpose probably co-opted by predators. Several chemicals that evaporate at different rates may allow deer to determine the age of tracks.

Preorbital glands appear as a pit in front of the eyes. (see fig. 1) In most African antelope, this gland produces a dark sticky substance used to mark territories. In Old World deer such as elk and particularly sambar, the preorbital gland is flared when the animal is excited whether it is in anticipation of food or during aggressive encounters. The function in whitetails and mule deer is less obvious but probably similar.

Diffuse glandular tissue is found on the forehead and may be used to mark the environment (for example when bucks thrash shrubs). Nasal and preputial glands have been discovered but their functions are unknown.

Visual communication

Chemical signals reinforce visual signals. The expressive behaviours of deer tend to be polar - for every signal there is an antithetical form with the opposite meaning. The most obvious poles are dominance, threat, courtship, and care-giving/soliciting behaviours. Within each polarity, there are degrees of escalation.

Dominance and threat mean different things to deer. Dominance displays are addressed to all and can be translated as “I am the greatest”. Threat is addressed to a specific individual and translates “I will fight you”. The opposite of dominance is supplication, the appropriate acknowledgement of a dominance display. A proud stance is complemented with a modest posture which reassures the sender that there is no contest.

Threat indicates preparedness to use weapons. Among antlered animals, it involves tipping the antlers towards another or, perhaps, to a nearby shrub.

For antlerless animals, it is the suggestion that they will raise a front hoof to strike or bite or rise on their hind legs to engage in a boxing match. Ears are lowered and chins are raised. Submission involves postures and signals that indicate that the individual has disarmed.

Courtship is one of the most complicated behaviours. Tending behaviour is the first sign and involves protecting an upcoming mating opportunity. Investigative behaviour such as the lip curl is ritualized. To further indicate his intent and to test the doe’s readiness, the buck will sometimes stiffly raise a front leg in a ritualized ‘mount’ known as Laufschlag.

We can expect our understanding of the expressive behaviour of deer to continue to evolve with a combination of insightful observation and sophisticated laboratory analysis.

Dr. Robert Hudson

Professor of Wildlife Productivity & Management

Renewable Resources

University of Alberta