Consider hearing as an example. Those of us who love the bush appreciate its unique sounds. The plaintive cry of jackal ushering in the African night, the haunting call of night jars or the hair standing on end effect brought on by the sound of lions roaring close by, elephant trumpeting and leopard sawing.

To lose one’s ability to hear is a tragic loss for one becomes cut off from so much that makes life worthwhile.

And what about going blind – how awful that must be. Our ability to see as with hearing is a very, very precious gift the value of which often only becomes apparent when we lose it partially or completely. Those who are deaf say they would gladly give up their sight to hear and those who are blind are often heard to remark that they would be willing to lose their hearing if they could only see again. The fact of the matter is that to lose any or part of one’s sensory abilities is indeed dreadful.

Sometimes loss of hearing or sight is progressive. My hearing is not what it used to be. After all my years of shooting (mostly without hearing protection!).

I have lost some hearing – especially in my left ear and I struggle to hear high frequency sounds. As we get older many of us end up having to acquire spectacles to read or to see at a distance as visual acuity begins to wane due to natural aging processes. Sometimes loss of a sensory faculty can be caused by disease or by inheritance.

I recently came across an interesting case and realised what effect it could have on ones hunting ability. I had been conducting the tracking module as part of a bow hunting course when I became aware of the problem.

One of the exercises given to students is to follow a prepared blood trail for a distance of about 100m. Exercises begin with an easy to follow trail with a lot of bright red blood sign indicating an animal bleeding profusely from an artery and then follow up exercises become progressively more difficult with infrequent and tiny drops of blood sign.

Most students follow the first trail with ease and arrive at the finish point within 5-10 minutes.

On this particular day I noticed one individual really struggling.

After half an hour he had made no progress at all but was ferreting around aimlessly and not making any headway. I joined him and asked if I could help. He replied in the affirmative. I took him over to where the first splash of blood was that was easily visible and pointed it out to him and told him to carry on.

A few minutes later he had made little if any progress. Either the individual had no ability to track whatsoever or else there was a problem. I took him to the next blood sign on the trail – once again easily visible and asked him to point it out to me. He could not and then the penny dropped – he was colour blind!

This is a genetic visual defect which can manifest itself in the person not being able to see certain colours in the visible light spectrum.

The student was red green colour blind. What we could see as a bright red colour against the background of green grass he perceived as grey on grey and it was invisible to him and hence his inability to be able to follow the trail.

Now the implications of this to the hunter are obvious. He will not be able to follow the blood trail of a wounded animal and will have to rely on a second person, guide or tracker to assist him.

Being red green colour blind will also make it difficult to spot wild animals that have a rufous (reddish) colouration. An impala will stand out starkly against a summer green or winter straw coloured background to someone with normal vision but will be more difficult to spot in a person who has a red green colour blindness defect.

Most herbivores are also red / green colour blind.

Hunters know how important it is to be able to track a wounded animal from blood sign. We try our best not to wound animals but being fallible human beings we do occasionally "botch a shot" and end up having to try and locate a wounded animal.

When an animal runs off after having been shot the hunter will always scout around the spot where the animal was last seen to search for some sign of blood which will confirm that the animal was indeed hit and will then look for the trail of blood sign which in some instances might be quite profuse and in other cases very scant, small and far apart, which will lead him either to within sight of the quarry to allow for a follow up shot or to the downed animal. We should also be able to follow up on wounded animals by observing other sign such as tracks, broken vegetation etc.

But the substrate does not always lend itself to this type of tracking and this is where the contrasting colour of red blood against a background makes things a little easier – for those that can see the colour red that is. If you are "blind" to the colour red, tracking blood sign becomes a virtual impossibility. How do you know if you are red / green colour blind? A Japanese researcher

Cleve Cheney is a wilderness trail leader, rated field guide instructor and the author of many leading articles on the subjects of tracking, guiding, bowhunting and survival. Cleve has unrivalled experience in wildlife management, game capture and hunting, both with bow and rifle. Click here to visit his site

developed what are known as Ishihara charts which help diagnose the defect. The charts to diagnose red / green colour blindness are shown in Figure 4. If you are unfortunate enough to be colour blind to certain wavelengths of the visible light spectrum you will have to rely on someone to assist you when tracking blood sign.

The lesson to be learned from this article? Give thanks – every day – for the faculties that you do have.