What Kinds of Animals Have Ultrasonic Hearing?

Definition

• Ultrasonic is a term that usually applies to anything above the frequency of normal audible sound for humans. Sound waves are measured in a frequency unit called the hertz, which is the number of cycles per second. Healthy humans hear in the 20 Hz to 20 kHz range, while ultrasonic sound is anything over 20 kHz. Some animals can hear sounds in the 20 to 100 kHz range. Medical science uses significantly higher frequencies in the 1 to 20 MHz range for ultrasound imaging of internal body structures.

Aquatic Animals

• A variety of aquatic animals use ultrasonics for communication and navigation. Some whales make clicks, whistles and pulsed calls in the 1 to 25 kHz frequency range. Pods, or groups of whales, have their own distinctive calls. Bottlenose dolphins also make sounds of 7 to 15 kHz for communication and short ultrasonic bursts of 20 to 170 kHz for echolocation. Some fish are able to hear the ultrasonic noises of these predators. Several species of clupeid fish, including the American shad and blueback herring, can detect noises up to 180 kHz. Also, at least one type of frog, the concave-eared torrent frog, emits noises in the 128 kHz range and does not have external eardrums.

Bats

• Bats use ultrasound to find food and navigate during flight. An Italian priest named Lazzaro Spallanzani performed the first nonaudible noise experiments on bats in the 18th century. He showed that bats could navigate during flight with blindfolds on but not with their mouths covered. The bat judges distance by emitting an ultrasonic noise, then measuring the time it takes to hear the sound bounce off a solid object. This is called echolocation. Bats can hear frequencies up to 100 kHz.

Insects And Rodents

• To avoid predation from bats, some types of insects can sense and use ultrasonics. The tiger moth can jam a bat's ability to hear the high frequencies by emitting its own ultrasonic blast. A few katydid species make ultrasonic sounds by rubbing their wings together. These chirps are in the 130 kHz range. Some shrews and mice use ultrasonic noises to communicate. Male mice "sing" in an ultrasonic range to attract females. Rats can make high frequency noises that indicate submissive and aggressive behavior. Rat young make distress calls of 30 to 50 kHz to attract their parents.