HUMANS VERSUS DEER – A BATTLE OF THE SENSES

The day was warm and breathlessly still and while standing looking at the plant, I heard thrashing coming from the sun-lit face above me, probably about 60m away, and where I knew that deer often bedded – it was obviously a stag! I stood and searched with my binoculars but couldn't see anything beyond 15m as the regrowth was just too thick. As I waited, though, the thrashing sounds got closer and closer, and finally, I could see movement in the scrub.

Meanwhile I had the safety off, ready to go. Eventually, after five minutes of heart-stopping suspense, I made out bits of the animal's head and a section of a heavy right antler. Smashed dogwood festooned its antlers.

I had the rifle up and was within a second of breaking the trigger when, with a loud ‘woof’, the stag turned and bolted, disappearing instantly into the scrub without giving the opportunity of a departing shot. Although there was no apparent breeze, my only conclusion was that my scent was wafting around in the gully and the stag had scented me – he had been just too close!

To get onto a stag in such dense scrub and to see its antlers adorned with broken vegetation was truly amazing. To almost pull it off a shot at a big angry stag made it doubly so. The stag had heard my stealthy approach, had assumed that I was a rival for his hinds’ favours and was coming to sort me out!

One key to deer hunting success is keeping the breeze in your face or at least across your front; you certainly don’t want it on your back. A deer might stand and look if it hears or sees you coming, but if it catches your scent there is only one result, it will bolt!

All animals (and humans too) are leaking sacks of chemicals, filling the air with great clouds of odorants (smells). Odorants are very diverse and are volatile chemical compounds of low molecular weight (less than 310). Despite the human nose being relatively insensitive, some common and familiar odorant chemicals that will be recognisable include indole and skatole (faeces), putrescine (rotting flesh), allicin (garlic breath), methanethiol (asparagus pee) and androstenone (sweaty socks).

If you are a deer hunter sneaking up a gully, a plume of scented air inevitably follows your every move. Likewise, with every footstep or brush against vegetation, you are leaving chemicals that signal your passing to a sensitive nose, perhaps for hours and potentially for days.

Similarly, a plume of scented air, foliage and tracks trail a deer everywhere it goes. As well as general body odours, deer have scent excreting glands that vary with species, often occurring on their hooves, lower legs and faces (pre-orbital glands for example). These specialised glands contribute to any scent trail.

Humans interact with their world primarily through sight – it is their trump card when hunting. On the other hand, many other mammals, including deer and dogs, have relatively poor eyesight but an extremely sensitive sense of smell. It is impossible to quantify precisely how good their scenting ability is, but at least 10,000 times better than that of a human’s is often quoted.

In the prey/predator world of deer and dogs there has been an arms race going back millions of years in which scenting ability was a key to whether you lived on one hand, or on the other, went hungry. Taking a dog for a walk will very quickly demonstrate how scent-orientated they are. When a dog sniffs it is not merely assessing the present but also reading the past and divining the future as well as reading biographies. Any deer, but particularly a sambar that evolved in dense jungle, is just the same. Its whole world is tuned to and revolves around scent rather than sight.

But what makes deer and dogs so good at reading and interpreting their world through scent? There are apparently a number of reasons; possession of noses that continually monitor scents independently of them breathing in and out, a large and convoluted nasal cavity, lots of odour detecting receptors and a brain with a large olfactory bulb to process and interpret signals.

Many animals, including deer, can also detect odorants called pheromones, chemicals that carry messages between members of the same species and are a key to their breeding strategy. These are detected by both the nose and by a structure called the vomeronasal organ. The vomeronasal organ has its own odour detecting cells and nerves with a very direct connection to the brain. In deer and other ruminants this organ is located in the nose above the roof of the mouth. When a deer curls back its upper lip to expose its teeth and block its nostrils (the so-called flehmen reaction), it’s sending inhaled odorants directly to the vomeronasal system, not to the nose.

Humans lack a vomeronasal system; it has presumably been lost during our evolution, probably because our senses have become dominated by sight, not smell.

When a deer is sniffing at a rub, scrape, preaching tree or wallow they are clearly ‘reading the book’ but just how detailed the information it is obtaining, we will probably never know. It seems likely, however, that they can identify the other deer that have visited in recent times, plus such information as their sex, age, place in the dominance hierarchy, health, stress level, sexual availability, food intake and recent travels.

“A deer might stand and look if it hears or sees you coming, but if it catches your scent there is only one result, it will bolt!”