Why Do Bats Make High-pitched Sounds?
Bats use high-pitched squeaks called ‘ultrasounds’ to find their way about. They are nocturnal animals. That is they move about by night. So they have developed their hearing to such an extent that they can find their way by a method known as echolocation. Not every species of bat is able to echolocate, but most can.
Although some bats make the squeaks needed for echolocation with their mouths, many send out sounds through their noses. Bats that echolocate with their nose often have special flaps and folds of skin on their faces called ‘nose leaves’. Scientists think that the nose leaves help the bats send the sounds in different directions. The nose leaves give the bats a rather odd appearance!
Bats have the best hearing of all land mammals. They often have huge ears compared to the rest of the body. The blind-flying abilities of bats were first studied by Lazzaro Spallanzani (1729-1799). He surgically removed the eyeballs from several bats to prove that they did not need to see to fly.
In the 20th Century, biologists, using electronic instruments, have carried out experiments with bats. They have discovered that bats find out where to go by emitting high-frequency sounds and receiving the echoes as they bounce off objects. Most of the sounds have too high a frequency to be heard by the human ear.
Bats commonly fly together in groups, but apparently they are not confused by the sounds and echoes produced by each other. When hunting in woods and in the rain they are able to discriminate between the faint echoes bouncing off insects and those bouncing off the ground, tree-trunks, branches, twigs and raindrops.