A fact that shows just how important the ability to hear is to all living things on the earth is that while scientists have discovered various kinds of amphibians, reptiles, fishes, and mammals who were blind, they've been unable to locate any naturally deaf species. But while the ability to hear is essential, animals don't need ears to hear; vertebrates have ears, but invertebrates frequently use other kinds of sense 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. One species known for its acute hearing is the elephant. Elephants have large ears, but they can also hear through their feet. This form of hearing is so acute that elephants can detect the sound of thunderstorms or the low-frequency call of other elephants coming from many kilometers 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. 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.

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 are recognized as having the most acute hearing among domesticated animals. They can hear sounds at lower and higher frequencies than humans can. A normal human range is 64 to 23,000 HZ. A normal cat range is 45 to 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. Echolocation is extremely precise. It only takes one chirp to determine an objects' size and location. Dolphins can use echolocation to detect objects the size of a small coin 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.

A quick look around the animal world is a great way to remind ourselves how vital hearing is.

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