97 Animal Ears-Mid

Animal Ears FOCUS Question How do the ears of different animals allow them to hear sounds?

Ears for Hearing What kinds of sounds do you hear in your everyday life? Perhaps your phone plays a song when a friend calls. You may listen to your favorite music on a computer. A bell likely marks the beginning and end of each school day. Your ears allow you to hear all the sounds that are important to you. Animals have different kinds of ears for hearing sounds that are important to them. How Sound Travels Sound is produced when tiny particles, called molecules, move back and forth, or vibrate Vibrating molecules cause the molecules next to them to vibrate, which is how sound travels. Sound can travel through gases, such as air, and also through liquids and solids.

Let Your Ears Stick Out Humans and other mammals such as cats, dogs, and bats have similar ears. The outer ears "catch" sound vibrations and send them to the eardrums. The eardrums then vibrate. The vibrations travel through three tiny bones in the middle ears. and then to the inner ears The cochleas (KOKE-lee-uz) change the vibrations into nerve impulses that are sent to the brain, which recognizes the sound. Most animals have two ears, one on each side of the body. Depending on where a sound is coming from, one ear hears it before the other. This feature helps animals locate sounds.

Ocean Vibrations Whales are mammals, too. Because they live in the ocean, their ears are built differently. In water, a human's entire skull vibrates when sound hits it. Both ears vibrate and hear sound at the same time. As a result, humans have a hard time locating sounds underwater. But in whales the bones of the middle and inner ears are outside the skull, so each ear vibrates separately in response to sound. One ear receives a sound before the other, and the sound is louder on that side. For this reason, whales know where a sound is coming from, even in the water. HOW WHALES HEAR 1. Sound vibrations from a fish travel toward a whale. 2. The vibrations enter the whale's lower jaw and then travel to the auditory bulla. 3. Nerve signals travel from the auditory bulla to the brain.

Floating Fish Ears Similar to a human's skull, a fish's entire body vibrates in water. So how can a fish detect sounds and tell where they are coming from? Each inner ear has three hard, floating bones. These bones are much heavier than the rest of the fish, so they move much more slowly in response to sound. The slower moving bones cause tiny hairlike structures in the inner ears to move. The fish's brain understands those movements as sound. Many fish have a swim bladder—an air-filled sac that helps them float in water. It is sensitive to sound waves. Fish that have inner ears close to their swim bladder hear better than other fish do. Fish that don't have swim bladders, such as sharks, can't hear as well.

Hearing with Echoes Bats use a process called echolocation to find prey. They send out clicks and listen for returning echoes to find moths and other insects to eat. The wrinkles in bats outer ears help them receive echoes and other sounds. The clicks that bats make are loud and high-pitched. Luckily, bats have a trick to avoid being deafened by their own clicks. A muscle makes the three tiny bones in the middle ear pull apart. The sound vibrations from the click are blocked. Then the muscle relaxes and the bones touch again—just in time to vibrate and let the bat hear the echoes! Try This Plug your ears as you shout "Echo!" Then quickly unplug them to hear your echo. You're hearing like a bat!