View source for Echolocation in bats

== How bats avoid obstacles ==

[[Image:echolocation in bats fig2.jpg|thumb|300px|Spectrogram (time-frequency plot) showing an FM echolocation sound of the big brown bat.  Each of the big brown bat’s signals is frequency-modulated (FM).  The direction of frequency sweep is downward, and each sound contains ultrasonic frequencies from about 20 kHz to about 110 kHz arranged in several harmonics (1st to 4th in this example). ]]

[[Image:echolocation in bats fig3.jpg|thumb|400px|Video images and sound emissions during interception of a flying June beetle.  This aerial interception was recorded with an infrared camera that is sensitive to body heat.  Both the bat and the flying beetle are warm, so they show up in the images (yellow arrow indicates image of beetle).  The bat’s sounds were recorded on the sound-track using a “bat detector,” an electronic device that picks up the ultrasonic broadcasts and translates them down to audible frequencies.  (The first such device was used to demonstrate the existence of echolocation by revealing that bats produced ultrasonic sounds in conjunction with experiments that showed the bat’s inner ear to respond to ultrasonic frequencies.)  Successive video frames show the bat’s location with respect to the insect as it approaches.  When searching for insects in open spaces such as over fields, big brown bats emit their sounds at intervals of 100-300 milliseconds (about 3 to 10 sounds/second).  When they approach the target, they decrease the interval to 30-50 milliseconds (about 20 to 30 sounds/second), and during the terminal stage, when the bat seizes the insect in its tail membrane, the interval decreases further to 7 to 10 milliseconds (about 100 to 140 sounds/second).  Bat detectors are used to study insect capture by bats because the stages of aerial interception are easily distinguished by ear.]]

[[Image:echolocation in bats fig4.jpg|thumb|400px|Photographs of the heads of different types of bats.  Bats belong to the mammalian order Chiroptera.  There are about 850 species of echolocating bats with different sonar signals according to the acoustic strategy they use for finding food and navigating in the dark.  Different species of bats emit their echolocation sounds either through the open mouth, as in the case of the big brown bat, or through the nostrils.  The area around the mouth or nose thus serves as a broadcasting horn, or antenna, while the ears serve as the receiving antennas.  The shapes of the heads of bats reflect their different designs for transmission and reception and usually are sufficient to identify the type of bat at a glance (left to right from top to bottom:  horseshoe bat, mastiff bat, Asian false vampire bat, spear-nosed bat, wrinkle-faced bat, spear-nosed bat,  sac-winged bat, spear-nosed bat, fishing bat).]]

[[Image:echolocation in bats fig5.jpg|thumb|400px|Head, ears, and auditory organs of the big brown bat.  (A) Face of big brown bat with mouth open to emit sound. (B) CATscan image of bat’s head with soft tissue in pink to show the outline of the external ear and its principal parts (pinna, tragus).  (C) CATscan image of skull to show the placement of the external ear for funneling sound down to the location of the tympanic ring, which supports the eardrum.  (D) MRI image of a cross-section of the bat’s head (coronal section) to show the thin skull, the thick muscles (for closing the mouth) overlying the skull, the location and relatively large size of the left cochlea and the right cochlea.  On the right side, several stages of the bat’s auditory system are labeled—the cochlea, auditory nerve (AN), cochlear nucleus (CN), nucleus of the lateral lemniscus (NLL), and inferior colliculus (IC).  These structures receive and process echoes to determine target features.  (E) A photomicrograph of a cross-section of the right cochlea (same orientation as in D) showing the auditory nerve (AN) and cochlear nucleus (CN).  The auditory nerve fibers are shown as yellow arrows (peripheral process, or dendrite, leading from the receptor cell to the cell body; central process or axon, leading from the cell body into the brain).  The striking feature of the bat is that its cochlea is located very close to the brain, so that the auditory nerve is much shorter than in most other mammals.]]

[[Image:echolocation in bats fig6.jpg|thumb|300px|Summary of acoustic imaging process in echolocation.  .........]]