BACKS TO THE WIND
Sounds and especially smells are carried by the wind. So, when outside and on the lookout, it makes sense to sit or stand with your back to the wind.
A picture of this would be an open fire, where it makes double sense not to sit in the smoke. So you sit with the fire downwind from you and the smoke blows away from you. Then you are able to smell and listen behind you, and look at the fire and any curious woodland creatures infront.
I don't know if this checks out in animal behaviour, but imagine it must. Animals who were only aware of what was upwind, i.e. always looking where the wind was coming from... would all have been eaten, by the predators who were downwind from them.
Please continue with Ancient and Modern Smells and Animal Rights