A fact that shows how important the ability to hear is to living species on earth is that while scientists have identified many types of reptiles, amphibians, fishes, and mammals who were sightless, they’ve been unable to locate any naturally deaf species. While the ability to hear is important, animals don’t need ears to hear; vertebrates have ears, but invertebrates often use other sorts of sense organs to hear.
In the case of insects, they have extremely sensitive tympanal organs which offer excellent hearing capabilities. Certain fly species can locate their prey exclusively via its song from a substantial distance. Hair can also be used to detect sounds. In spiders, cockroaches and caterpillars, tiny hair cells play the role of ears. The spiders and cockroaches have the hairs on their legs, while the caterpillar has them along 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.
Fish are interesting too. Fish don’t have ears, but are able to perceive sounds underwater using lateral lines that run horizontally along the length 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.
Many animals not only hear better than we do, they hear more sounds, easily detecting sounds in frequency ranges far below or above the frequencies that we humans can hear. Among domesticated animals, cats have the sharpest hearing, and can hear frequencies between 45 Hz and 64,000 Hz (humans can hear frequencies between 64 Hz and 23,000 Hz). Birds also have acute hearing, especially owls, whose hearing is not only far better than ours, but more precise in its ability to locate the source of the sound. An owl can pinpoint the exact location of a scurrying mouse in less than 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. Dolphins can use echolocation to detect objects the size of a small coin over 70 meters away. Bats can hear insects flying up to 30 feet away, in total darkness, and then catch them in mid-air…now that is hearing.
The animal world provides some excellent example to remind ourselves how important the sense of hearing is.
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