The ability to hear is important to just about all living creatures; even though scientists have found many species of sightless fishes, amphibians, reptiles, and mammals, no deaf vertebrate species have ever been identified. But while hearing is important, animals don’t need ears to hear; vertebrate animals have ears, but invertebrate animals frequently use other sorts 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. 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.
Even though fish don’t have ears (they perceive sounds using lateral lines that run horizontally along their bodies), they can detect sounds that humans would not be able to hear. 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 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.
Echolocation is an extension of hearing often considered it own sense since it functions like sonar. Bats and dolphins emit small click or chirps which bounce off of surrounding objects and return to them. They are essentially using sound waves as a tool to “see” their surroundings. Echolocation is extremely precise. It only takes one chirp to determine an objects’ size and location. A dolphin is able to detect a coin at a distance of 70 yards always. 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.