An interesting observation that indicates just how important hearing is to living species on the earth is that while scientists have identified various kinds of amphibians, reptiles, mammals, and fishes who are sightless, they have been unable to locate any naturally deaf species. However, it doesn’t take ears to hear. Sounds waves – which are nothing more than vibrations in the air – can be perceived in a variety of ways. Vertebrate animals have ears. But, invertebrates possess other sensory organs to detect sounds.
Insects, for example, have tympanal organs that work as well as ears, and in fact give them far better hearing than humans; as an example, a species of fly that is a parasite to crickets can locate its prey at some distance just by hearing its song. In some species, tiny hairs take the place of ears; in spiders and cockroaches these hairs are on the legs, while in caterpillars they are along the surface of its body. Some animals have two ways of processing sound vibrations. For example, an elephant has extremely large ears, but it also takes in sound information via its feet. Elephant feet are sensitive to the very low frequency calls of other elephants and also the rumble of thunder many miles away.
Sound travels both faster and farther through water than it does through the air, and even though fish don’t have ears, they can effectively detect sounds using lateral lines that run horizontally on the sides of their bodies. A marine mammal, dolphins have no ears, but have eardrums on the outside of their bodies that give them the best sense of hearing among animals, over 14 times better than human hearing.
Not only do many animals have better quality hearing than humans, they can hear more sounds, detecting frequency ranges that are much higher and lower than the range that humans are capable of hearing. Cats have the most acute hearing among animals we have domesticated as pets; while humans can only hear sounds between 64 and 23,000 Hz, cats can hear sounds between 45 and 64,000 Hz. Birds, especially owls, have excellent hearing. Owls are particularly skilled at detecting the precise location of a sound – and detecting it very quickly. They can pin-point the origin of a mouse scurrying in under 0.01 seconds. Some species, such as bats and dolphins, extend their hearing abilities by using a form of sonar called echolocation, in which they emit ultrasonic chirps or clicks, and then interpret the sound waves as they return from objects the waves strike. This echolocation is so precise that with a single chirp, a dolphin or bat can tell the exact location, direction, size, and even the physical nature of objects in its environment. A dolphin is able to detect a coin at a distance of 70 yards always. A bat can detect an insect 30 feet away in complete darkness.
The animal world provides some excellent example to remind ourselves how important the sense of hearing is.