This time, we will consider the sound frequencies used by living creatures in their daily lives. The audible range for humans is said to be 20Hz to 20kHz. Sounds below 20Hz are called the infrasonic range, and sounds above 20kHz are called the ultrasonic range. Naturally, the frequencies used by living creatures for communication are within the audible range that they can hear. The sounds they make for communication are produced by vibrating parts of their bodies. Whales and elephants, which need to communicate over greater distances, use the infrasonic range. Infrasonic sound has energy and can travel farther, making it advantageous for communicating with distant companions. Whales and elephants share useful information with distant companions through long-distance communication. Because sound vibrations are transmitted more efficiently through water than through air, infrasonic sound can travel farther underwater than through air. This is because molecules are denser in water, the speed of sound is faster, and there is less attenuation.
Aquatic creatures use low-frequency bands for communication because sound transmission is more efficient underwater. On the other hand, bats and moths are representative examples of organisms that utilize the ultrasonic range. Moths, in particular, are the organisms most able to distinguish sounds in the ultrasonic range. Moths have developed ultrasonic hearing to protect themselves from bats, using the antennae protruding from their heads to detect the ultrasonic sounds emitted by bats, their predators. Cats and dogs, which live alongside humans, can also hear ultrasonic sounds above 20 kHz, which humans cannot hear. Cats are sensitive to creatures that emit high-frequency sounds with their wings because they can hear ultrasonic sounds. In this way, each organism develops hearing adapted to the environment in which they live in order to survive as a living being. We believe that learning about the sensory characteristics of organisms that have evolved to suit their natural environment will be useful for developing a better human society.