page_title: Bat
section_title: Echolocation
hierarchical_section_title: Bat / Anatomy and physiology / Senses / Echolocation
context_page_description: Bats are mammals of the order Chiroptera. With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more manoeuvrable than birds, flying with their very long spread-out digits covered with a thin membrane or patagium. The smallest bat, and arguably the smallest extant mammal, is Kitti's hog-nosed bat, which is 29–34 millimetres in length, 150 mm across the wings and 2–2.6 g in mass. The largest bats are the flying foxes and the giant golden-crowned flying fox, Acerodon jubatus, which can weigh 1.6 kg and have a wingspan of 1.7 m.
  The second largest order of mammals after rodents, bats comprise about 20% of all classified mammal species worldwide, with over 1,400 species. These were traditionally divided into two suborders: the largely fruit-eating megabats, and the echolocating microbats. But more recent evidence has supported dividing the order into Yinpterochiroptera and Yangochiroptera, with megabats as members of the former along with several species of microbats. Many bats are insectivores, and most of the rest are frugivores or nectarivores.
context_section_description: Microbats and a few megabats emit ultrasonic sounds to produce echoes. Sound intensity of these echos are dependent on subglottic pressure. The bats’ cricothyroid muscle controls the orientation pulse frequency, which is an important function. This muscle is located inside the larynx and it is the only tensor muscle capable of aiding phonation. By comparing the outgoing pulse with the returning echoes, the brain and auditory nervous system can produce detailed images of the bat's surroundings. This allows bats to detect, localise, and classify their prey in darkness. Bat calls are some of the loudest airborne animal sounds, and can range in intensity from 60 to 140 decibels. Microbats use their larynx to create ultrasound, and emit it through the mouth and sometimes the nose. The latter is most pronounced in the horseshoe bats (Rhinolophus spp.). Microbat calls range in frequency from 14,000 to well over 100,000 Hz, extending well beyond the range of human hearing (between 20 and 20,000 Hz). Various groups of bats have evolved fleshy extensions around and above the nostrils, known as nose-leaves, which play a role in sound transmission.
  In low-duty cycle echolocation, bats can separate their calls and returning echoes by time. They have to time their short calls to finish before echoes return. Bats contract their middle ear muscles when emitting a call, so they can avoid deafening themselves. The time interval between the call and echo allows them to relax these muscles, so they can hear the returning echo. The delay of the returning echoes allows the bat to estimate the range to their prey.
  In high-duty cycle echolocation, bats emit a continuous call and separate pulse and echo in frequency. The ears of these bats are sharply tuned to a specific frequency range. They emit calls outside this range to avoid deafening themselves. They then receive echoes back at the finely tuned frequency range by taking advantage of the Doppler shift of their motion in flight. The Doppler shift of the returning echoes yields information relating to the motion and location of the bat's prey. These bats must deal with changes in the Doppler shift due to changes in their flight speed. They have adapted to change their pulse emission frequency in relation to their flight speed so echoes still return in the optimal hearing range.
  In addition to echolocating prey, bat ears are sensitive to the fluttering of moth wings, the sounds produced by tymbalate insects, and the movement of ground-dwelling prey, such as centipedes and earwigs. The complex geometry of ridges on the inner surface of bat ears helps to sharply focus echolocation signals, and to passively listen for any other sound produced by the prey. These ridges can be regarded as the acoustic equivalent of a Fresnel lens, and exist in a large variety of unrelated animals, such as the aye-aye, lesser galago, bat-eared fox, mouse lemur, and others. Bats can estimate the elevation of their target using the interference patterns from the echoes reflecting from the tragus, a flap of skin in the external ear.
  By repeated scanning, bats can mentally construct an accurate image of the environment in which they are moving and of their prey. Some species of moth have exploited this, such as the tiger moths, which produces aposematic ultrasound signals to warn bats that they are chemically protected and therefore distasteful. Moth species including the tiger moth can produce signals to jam bat echolocation. Many moth species have a hearing organ called a tympanum, which responds to an incoming bat signal by causing the moth's flight muscles to twitch erratically, sending the moth into random evasive manoeuvres.
caption: Principle of bat echolocation: orange is the call and green is the echo