Hearing is essential to almost all living creatures; although scientists have discovered many species of blind amphibians, fishes, reptiles, and mammals, no deaf vertebrate species have ever been identified. But while the ability to hear is essential, one doesn’t necessarily need ears to hear; vertebrates have ears, but invertebrates often use other kinds of sensory organs to hear.
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. Spiders and cockroaches have tiny hairs on their legs that they use to pick up sounds, and caterpillars have similar sound-receiving hairs on their bodies. 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. Dolphins have external eardrums on the outsides of their bodies that are so sensitive that they have the best sense of hearing among animals, and are able to hear 14 times better than humans.
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. 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. Owls also have phenomenal hearing, both in terms of acuity and reaction time; they can detect 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. Scientists have proven that by using echolocation dolphins can detect objects the size of a small coin from over 70 meters away. And if you want a real display of hearing, bats can not only hear insects flying 30 feet away from them, they can then pursue and catch them in mid-air, all in total darkness.
The animal world provides some excellent example to remind ourselves how important the sense of hearing is.
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