While many bats navigate using ultrasound frequencies, bats are better described to navigate via echolocation. Ultrasound can be defined as frequencies that are higher than the normal human range of audibility.
The frequency of bats' echolocation ranges from 20 to 200 kHz. Sounds generally remain audible to humans up to 20 kHz. Most of the sounds that bats emit fall within the ultrasonic range, beyond the range of human audibility. However, the low frequencies produced fall within the human range of hearing and are not ultrasonic.
Most bats produce echolocation calls using a combination of constant as well as modulated frequencies, meaning the frequency of the pitch changes as the bat echolocates. Because low frequencies travel greater distances than high frequencies, they allow bats to receive information from greater distances. Bats use high frequencies more often, as they provide more detailed information such as the location, size, speed and direction of prey.
Bats use echolocation in conjunction with vision. The majority of bats are able to produce echolocation sounds by manipulating their voice box, or larynx. However, a few species of bats echolocate by clicking their tongues. Bats omit the sounds they produce from either their mouth or nose. A bat processes all of this information unconsciously.