The way animals perceive the world around them varies greatly. The senses that each animal has, and the degree of specialisation of those senses, are good indicators of their requirements out in the wild. Our own human senses share fundamental similarities with other vertebrates, however the extent to which each of these senses has specialised across vertebrate species is the product of distinct evolutionary histories giving rise to adaptations which are specially tailored to the animals’ unique needs. Indeed, it can often be hard for us to even begin to imagine what it would be like to have the sensory capacities of certain animals. On the other hand some animals have sensory capabilities quite similar to ours, making direct comparisons relatively easy. Cats and dogs for example see the world largely the same way as we do, although a greatly reduced number of cone photoreceptors in their retina means that they have poor colour vision. Instead, they have far more rod photoreceptors, which gives them far better vision in low light conditions, an adaptation which is useful for nocturnal hunting. Dogs also have a highly sensitive olfactory system which features 300 million receptors in their nose compared to the six million in our own. This can be attributed to their wild ancestors, who would have required a keen sense of smell to track down prey. Cats have far more sensitive ears than both dogs and humans, showing once again that there is often a trade off in the level of specialisation that each of the senses can feasibly have, probably owed to the increased energetic costs associated with having specialised senses.
Of all vertebrates, birds have the most specialised vision. Many species are capable of seeing more colours than humans and some can even see light in the ultraviolet (UV) spectrum. Light exists on a broad electromagnetic spectrum and humans can see light between about 380 and 740 nanometers but UV light is lower on the spectrum, between ten and 400 nanometers. In most cases, this enhanced capacity has evolved for specific purposes relating to feeding strategies. Greater colour perception allows for food items to be identified more readily in insect and fruit eating birds, while UV perception is thought to give nocturnal birds, such as owls, the ability to detect rodent prey by tracking their urine. Certain birds such as penguins and even some garden birds are now known to use UV vision to detect visual differences between the sexes, which are undetectable to us. The benefits conferred by these signals is that it allows the birds to have adaptations which are inconspicuous to other animals, while retaining the ability to make distinctions between themselves.
“Certain dolphins will even use echolocation to graze along the seafloor.”
Another impressive visual capacity found in birds is that they have a far higher flicker fusion threshold (FFT) than is found in humans, giving them what can be described as “ultra-vision”. Humans have a flicker fusion threshold of about 60 Hz which means that we are capable of forming an image of what we are seeing 60 times per second. Certain birds have been shown to have FFTs as high as 145 Hz, allowing them to essentially refresh the visual details of their surroundings at a far greater rate than us. While it was already known that flying insects showed the same capacity for high FFTs, it is only in recent years that studies have begun to look at this capacity in birds. Flight requires rapid and precise responses and this heightened visual capacity has evolved separately in both groups in response to the same fundamental requirements, a phenomenon known as convergent evolution.
Although they also fly, bats have overcome the problem of navigating the air through echolocation, an adaptation which is more effective than vision given that they are largely nocturnal. By emitting sounds which then reflect off their surroundings to produce echos, echolocation allows bats to form a three dimensional image of their environment, granting them unparalleled agility in the air especially when combined with their unique wing structure. Insectivorous bat species also use echolocation to pinpoint the location of fluttering insects. The capacity for echolocation is also found in cetaceans such as whales and dolphins and is actually associated with modifications to the same exact auditory gene known as prestin in both groups, despite the fact that their last common ancestor lived 200 million years ago. As an example of convergent evolution, the emergence of echolocation is of particular interest since it reveals that certain genes have a predisposition to be modified for certain functions based on their original characteristics. It is worth noting that both bats and cetaceans live in three dimensional environments, and so the ability to form an auditory image of the surroundings is of great benefit. Like bats, cetaceans also use echolocation to find and hunt prey. Dolphins have phonic lips, which aid them in communication and hunting through a series of clicks and whistles. The clicks, which can be as many as 500 per second, are used to pinpoint prey, and fat pads on the lower jaw act as receivers for the echos generated. Certain dolphins will even use echolocation to graze along the seafloor, essentially using it to look for any prey items hiding underneath the sand by identifying inconsistencies in the auditory reflections.
“We may end up losing many of them before we have even fully understood their unique qualities.”
Complex sensory capacities are by no means limited to the higher vertebrates. A group of fish known as elasmobranchs, which includes sharks and rays, contain certain species which are capable of using electromagnetism to locate prey. By having electroreceptors in their snout, animals like sawfish, for example, can detect the electromagnetic field emitted by their prey, thereby giving them the ability to find prey buried in sediment on the seafloor in a similar way to dolphins. Sawfish also have tiny canals on their skin which contribute to their hunting ability by allowing them to detect water movements while seeking prey. The characteristic saw-like snout is then used to stun and pierce its prey before it is ultimately ingested.
Our knowledge on the sensory capacities of animals is still limited, and while it is impossible to fully appreciate what it would be like to enjoy such abilities, it is impressive to see just how extraordinary the products of evolution can be. With many species facing ever-growing threats due to human activity via habitat loss, climate change, and overfishing, we may end up losing many of them before we have even fully understood their unique qualities. When it comes to our responsibility towards the natural world, we must realise that, irrespective of whether they confer any direct benefits on us, conservation measure play a vital role in reminding us of our place in nature and fostering our underlying desire to nurture and discover it in all its wonders.
