Background
The phrase "blind as a bat" does not actually apply to these flying creatures. While they can see almost as well as we can, bats primarily use echolocation in order to hunt for insects as they soar through the night sky. The amount of time it takes the sounds to travel back to them after bouncing off their prey indicates how far away it is. Echolocation is also used in all species of bats to navigate through the night in order to avoid obstacles and find their way to their habitat. Though all bats use this mechanism, the frequency at which they produce these sounds as well as how the sounds are produced differ between particular species.
The phrase "blind as a bat" does not actually apply to these flying creatures. While they can see almost as well as we can, bats primarily use echolocation in order to hunt for insects as they soar through the night sky. The amount of time it takes the sounds to travel back to them after bouncing off their prey indicates how far away it is. Echolocation is also used in all species of bats to navigate through the night in order to avoid obstacles and find their way to their habitat. Though all bats use this mechanism, the frequency at which they produce these sounds as well as how the sounds are produced differ between particular species.
Producing Sounds
Most all bats produce the sounds for echolocation by contracting their voice box, or larynx. The sound is emitted through their mouths and echoes through the air. Some bats, however, click their tongues to produce the sound, which is also emitted through their mouths. Two exceptions are the Horseshoe Bat (Rhinolophidae, below left) and the Old-World leaf-nosed bat (Hipposideridae, below right), which emit sounds through their specially adapted noses shaped like megaphones.
Most all bats produce the sounds for echolocation by contracting their voice box, or larynx. The sound is emitted through their mouths and echoes through the air. Some bats, however, click their tongues to produce the sound, which is also emitted through their mouths. Two exceptions are the Horseshoe Bat (Rhinolophidae, below left) and the Old-World leaf-nosed bat (Hipposideridae, below right), which emit sounds through their specially adapted noses shaped like megaphones.
Frequency and Intensity of Sounds
The frequency at which bats produce sounds for echolocation ranges from 20 to 200 kilohertz (kHz). To put things in perspective, humans can usually only hear sounds around 20 kHz. However, the intensity, or loudness, of the sounds emitted from bats can range from 50 decibels (dB) to 120 dB. A sound at 120 dB can be compared to a smoke detector going off 10 cm from your ear, which is enough to damage human hearing (Van Ryckegham). However, because sounds of this decibel level are emitted at such a high frequency, we are unable to hear them.
The frequency at which bats produce sounds for echolocation ranges from 20 to 200 kilohertz (kHz). To put things in perspective, humans can usually only hear sounds around 20 kHz. However, the intensity, or loudness, of the sounds emitted from bats can range from 50 decibels (dB) to 120 dB. A sound at 120 dB can be compared to a smoke detector going off 10 cm from your ear, which is enough to damage human hearing (Van Ryckegham). However, because sounds of this decibel level are emitted at such a high frequency, we are unable to hear them.
Receiving Sounds
The most basic adaptation bats have for receiving sounds in the echolocation process is the shape of their ears. Bats' ears are large, wide and somewhat cone-shaped which makes it easier for signals to be heard. Additionally, for echolocation to be effective at varying frequencies and intensities bats ears must be very sensitive to subtle changes in sound. This is assisted by the concentration of receptor cells in the inner ear that can detect changes in frequency as little as 0.0001 kHz.
To assist the bats in hearing the reverberation or echoes of their emission without it being muffled by the emission itself, the middle ear contracts to separate the mallues, incus and stapes.
The most basic adaptation bats have for receiving sounds in the echolocation process is the shape of their ears. Bats' ears are large, wide and somewhat cone-shaped which makes it easier for signals to be heard. Additionally, for echolocation to be effective at varying frequencies and intensities bats ears must be very sensitive to subtle changes in sound. This is assisted by the concentration of receptor cells in the inner ear that can detect changes in frequency as little as 0.0001 kHz.
To assist the bats in hearing the reverberation or echoes of their emission without it being muffled by the emission itself, the middle ear contracts to separate the mallues, incus and stapes.