HUMANS VERSUS DEER – A BATTLE OF THE SENSES

Meanwhile I stared at the wall of scrub and trees forty metres in front of me, frustrated that I could not see any part of the sambar that had me well and truly pegged.

It didn’t matter what I did, stay put, take a very slow step sideways, stretch on tip-toes or climb gingerly onto a tree stump, the result was the same – I was snookered – I could not see any part of the deer, even though it could obviously see me and identified me as a potential threat.

After ten minutes and maybe twenty honks, the encounter ended with the deer quietly moving off, still unseen, probably not because it caught my scent but more likely because it had had enough and couldn’t decide whether I was a threat or not. Meanwhile my hunting companion, who was across the river and hundreds of metres away had heard the staccato barks and had waited expectantly for the boom of a rifle shot that never came.

As humans, our senses are dominated by our ultra-sensitive eyesight and when this key ability fails, we can sometimes fall back on hearing. In the scenario described both senses failed me. It was all very, very frustrating!

On the other hand, the deer had its problems too! Although it had me pegged as a potential threat it clearly wasn’t sure whether I was a dangerous predator or not. Its dominant sense, that of smell, was of no use as the breeze was drifting to me, and while it had probably heard both my slow approach and seen my blurred outline, neither proved that I wasn’t a harmless cow, kangaroo or wallaby.

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We humans investigate our world through five main senses, sight, sound, taste, smell and touch. Sight is by far our greatest asset when hunting and we are naturally biased when we are out in pursuit of deer – we tend to assume that their senses, apart from scenting ability, are similar to ours. However, human vision outshines almost every other animal’s in its ability to resolve detail.

If you give a ‘thumbs up’ at arm’s length your nail covers around one degree or sixty minutes of angle. Human eyes can distinguish 60 to 70 thin lines on that one degree, or about one line per minute of angle. By contrast deer can only distinguish around 10 lines per degree which puts their visual acuity on the level at which a human can be classed as legally blind. The detail that a deer can see at 40 metres, a human can see at around 400 metres!

Deer eyesight, although of low acuity, covers around 300 degrees in a horizontal plane and is really sensitive to movement (there is a trade-off between sensitivity and acuity). It is also very good in poor light, at dawn and dusk and through the night, important feeding times. These features are keys to survival in a prey species. One downside of having eyes on the sides of your head is poor depth perception compared to humans and other predators.

The other sense at play in the above encounter was hearing. The deer had almost certainly heard my approach as there is no doubt that a sambar’s hearing is very acute. Once I stopped though any sounds that I had been making ceased. On the other hand, the sambar had bombarded me with an ongoing series of incredibly loud honks, which normally would have allowed me to home in on the animal.

On investigating human hearing, what I found goes some way to explaining my failure to identify the source of the honking. Humans can usually locate the origin of sounds to within two degrees in the horizontal plane, but only three to six degrees in the vertical plane. My sambar encounter at around 40 metres means that the honks could have been coming from an area 1.2 metres wide by up to 3.6 metres high. Whether deer with their large mobile ears are better than humans at pinpointing sounds in both the horizontal and vertical planes isn’t clear but seems likely.

So, while I couldn’t spot the sambar hidden in the dense scrub, it couldn’t identify me as an armed hunter either, so long as I kept my movements silent, slow and very deliberate and so long as the breeze remained in my favour.