Hearing is important to almost all living creatures; although scientists have found several species of blind amphibians, fishes, mammals, and reptiles, no deaf vertebrate species have ever been discovered. However, it doesn’t take ears to hear. Sounds waves – vibrations in the air – can be detected in a variety of ways. Vertebrates have ears. But, invertebrates have developed 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. 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. 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. 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.
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.