Animal Senses
There's a lot of mythology about the extreme acuteness of animal senses. Some animals, particularly lone predators such as eagles, do indeed have extremely acute individual senses.
But most animals rely - like we do - on a cluster of individual fairly ordinary senses to infer whether a phenomenon is dangerous, beneficial or neutral. They are, however, generally very attentive to what is going on round them - they notice the unusual and usually respond to it as a potential threat.
Because much of the time we are quite unaware of our obtrusiveness in the wild, we assume that animals have extremely acute senses, whereas the reality is that we are just making ourselves terribly obvious. But different animals do indeed sense the world in very different ways. So nothing beats knowing about the sensory capacities of the species you expect to encounter.
Different animals have very different ways of seeing the world. Dogs have two-colour vision roughly corresponding to blue and yellow in our terms. Many birds can detect ultra-violet as well as the red, green and blue we are familiar with. Deer see day glow orange as a nondescript dark brown. These differences have serious implications for concealment camouflage, as what seems to blend into the background to us may stick out like a sore thumb to other creatures. A classic problem results from washing one's expensive bird watchers' camouflage jacket. Most commercial washing powders contain brightening agents - substances that absorb ultra-violet light and re-emit in the extreme violet to make white shirts look "cleaner" - a similar effect to that of the "black light" in a disco. So although the washed jacket may look no different you, in direct sunlight it may positively glow as far as the birds are concerned.
Shape and contrast are also important. Almost all animals can recognise silhouettes and some seem to be very strong signals. The scarecrow works (if at all) not by looking like a person in detail but by presenting a silhouette that triggers a flight response. The same can be accomplished by raising one's arms horizontally. It's even possible that "human" is not the significant factor - many predatory birds present a cruciform silhouette in flight when seen from below.
So colour shape and contrast are important, but movement is a primary visual trigger for most animals - indeed frogs can't detect stationary objects at all in certain parts of their visual field.
The hearing of many animals seems much more acute than that of the typical urban human, but that's not necessarily due to an intrinsic difference in the physiology. The reality is that quite independent of the physical limits of the ear, most of us have extremely degraded auditory perception because of our acclimatisation to a noisy environment.
Wild animals, living as they do both in a quieter environment and permanently either under threat of becoming someone else's dinner if they are a prey species or failing to catch their dinner if they are predators, are necessarily much more alert - those that weren't got eaten or starved already. So little sounds that we would probably ignore may be very detectable to other creatures, not because their physical hearing is intrinsically better, but because they are paying much more attention to what is going on round them than we tend to. That said, different animals hear over dramatically different frequency ranges, so relatively powerful sounds in certain frequency bands that may be inaudible to us can be heard easily other creatures - witness the dog whistle. When you step on a twig, the sounds heard by you and the animal in front of you may not be the same.
The sense of smell is probably the one that is most refined in many animals compared with ours. Moths can apparently detect single molecules of moth pheromones hundreds of yards from their source. Deer respond swiftly to any stalker unwise enough to be caught upwind of the herd, even at distances of up to half a mile. Drenched as most of us are in a cocktail of synthetic "fragrances" from deodorant to toothpaste and washing powder, we either have to stay down wind or radically change our habits if we want to remain undetected in the wild.
Because much of the time we are quite unaware of our obtrusiveness in the wild, we assume that animals have extremely acute senses, whereas the reality is that we are just making ourselves terribly obvious. But different animals do indeed sense the world in very different ways. So nothing beats knowing about the sensory capacities of the species you expect to encounter.
Vision
Different animals have very different ways of seeing the world. Dogs have two-colour vision roughly corresponding to blue and yellow in our terms. Many birds can detect ultra-violet as well as the red, green and blue we are familiar with. Deer see day glow orange as a nondescript dark brown. These differences have serious implications for concealment camouflage, as what seems to blend into the background to us may stick out like a sore thumb to other creatures. A classic problem results from washing one's expensive bird watchers' camouflage jacket. Most commercial washing powders contain brightening agents - substances that absorb ultra-violet light and re-emit in the extreme violet to make white shirts look "cleaner" - a similar effect to that of the "black light" in a disco. So although the washed jacket may look no different you, in direct sunlight it may positively glow as far as the birds are concerned.
Shape and contrast are also important. Almost all animals can recognise silhouettes and some seem to be very strong signals. The scarecrow works (if at all) not by looking like a person in detail but by presenting a silhouette that triggers a flight response. The same can be accomplished by raising one's arms horizontally. It's even possible that "human" is not the significant factor - many predatory birds present a cruciform silhouette in flight when seen from below.
So colour shape and contrast are important, but movement is a primary visual trigger for most animals - indeed frogs can't detect stationary objects at all in certain parts of their visual field.
Hearing
The hearing of many animals seems much more acute than that of the typical urban human, but that's not necessarily due to an intrinsic difference in the physiology. The reality is that quite independent of the physical limits of the ear, most of us have extremely degraded auditory perception because of our acclimatisation to a noisy environment.
Wild animals, living as they do both in a quieter environment and permanently either under threat of becoming someone else's dinner if they are a prey species or failing to catch their dinner if they are predators, are necessarily much more alert - those that weren't got eaten or starved already. So little sounds that we would probably ignore may be very detectable to other creatures, not because their physical hearing is intrinsically better, but because they are paying much more attention to what is going on round them than we tend to. That said, different animals hear over dramatically different frequency ranges, so relatively powerful sounds in certain frequency bands that may be inaudible to us can be heard easily other creatures - witness the dog whistle. When you step on a twig, the sounds heard by you and the animal in front of you may not be the same.
Smell
The sense of smell is probably the one that is most refined in many animals compared with ours. Moths can apparently detect single molecules of moth pheromones hundreds of yards from their source. Deer respond swiftly to any stalker unwise enough to be caught upwind of the herd, even at distances of up to half a mile. Drenched as most of us are in a cocktail of synthetic "fragrances" from deodorant to toothpaste and washing powder, we either have to stay down wind or radically change our habits if we want to remain undetected in the wild.