Animal echolocation

Echolocation in animals, also called biosonar, is a special form of echolocation used by animals. It serves the orientation of an animal in space, by actively sending out sound waves and then receives the echo and analyzed. This capability is particularly pronounced in bats, the so- locate insects, as in toothed whales, which adjust with the echolocation fish. In primitive expression is echolocation found in some insectivores and birds. The echolocation allows the orientation in low-light habitats or at night.

History of Research

The Italian Lazzaro Spallanzani observed in 1793 that bats can also be based blindfolded in the dark, and the Swiss Karl Jurine proved experimentally in 1794 that bats with sealed by wax ears are disoriented in the dark. Both postulated a connection between orientation in the night and the sense of hearing, but public doubt by Georges Cuvier made ​​their theses soon forget. In 1938, scientists Donald R. Griffin, George W. Pierce and Robert Galambos began to study the orientation of the bats in the dark. Crucial in their investigations proved to newly developed piezo- electric crystals, with the aid of ultrasound can be converted into audible for humans frequencies. Griffin and his colleagues were able to explain the positioning mechanism and coined the term echolocation (English echolocation ). Echolocation in toothed whales in 1947 for the first time suspected and confirmed experimentally in 1960.

General

All echolocating animals use the same principle: send sound waves, these are reflected by objects in the environment and added the echo from the ear. The brain processes the information to an image of the environment, and determines the relative position of the animal to surrounding objects. These usually high frequency, often lying in the ultrasonic sounds are used because they are thrown back by their short wavelength and small objects and enable a higher resolution. A echoortendes animal must therefore be able to perceive high-frequency sound. The relative position of an object can be determined by two basic parameters: distance and direction. Sound travels at the speed of sound () continues - from the difference in time between the emission of the sound signal and arrival of the echo () can close the animal on the distance to the object:

The localization of the direction ( Hörereignisrichtung ) is determined by spatial hearing, without emitting sound waves. The approach here differs from animal to animal group group. In contrast echolocation requires a very fast impulse conduction in the nervous system, as a echoortendes animal must process many signals in a short time and to accurately determine distances accurate time distinctions are necessary.

The echolocation arose independently ( convergent ) in several animal groups. Although her ​​to use various organ systems, shows, despite only distant relatives a strong similarity in the protein Prestin of toothed whales and bats. Prestin is responsible for the sensitivity and the adaptation to certain frequencies of the ear.

Systems for echolocation

Bats

Bats ( Microchiroptera ) produce laryngeal echolocation in the frequency range of 8-160 kHz depending on the type. These rely mostly on the mouth of the body, in some groups, such as the horseshoe bats, however ( Rhinolophidae ) on the nose. In such bats special outgrowths of the nasal focus the sound. To catch the echoes bats have a highly developed ear and big ears. The vertical alignment of the object to determine the bat bats either by interference caused by the tragus or by the independent raising and lowering of the ears. The horizontal origin of echoes identify bats by the difference of arrival and signal strength between the two ears. Bats adjust their positioning cries of the distance of their prey: To discover distant prey, they encounter narrow (a few frequencies containing ), long tones. Nearby are broadband ( containing many frequencies), used less than 5 ms lasting calls that allow a very precise localization. In this way, frequency modulating bats are called FM - bats ( frequency modulated ). Some bats use only constant frequencies, they are classified as CF (constant frequency). The middle ear muscle of bats contracted when calling - Bats must therefore keep their calls short. Otherwise their middle ear muscles would be upon arrival of the echoes still curious, so the bat deaf. In many species, echolocation is so well developed that the size and nature of a prey animal can be determined very accurately. The distance can be determined only 10-12 ns very closely some species by time differentiation of manifest. Echolocating bats develop a spatial memory over time by echolocation. So you have a three-dimensional image of their habitat " in the head" and can be oriented so that, even if they do not emit echolocation.

In the closely related bats ( Megachiroptera ) only the genus Rousettus has the ability to echolocation. These bats do not produce their sounds in the larynx, but produce with her tongue clicks of 0.6-1 ms duration and frequencies of 12-70 kHz.

Toothed whales

There are several theories for sound production in toothed whales. It has not yet fully confirmed until today. The main theories on the generation of the sound, and it is forwarded into the water, the larynx and the theory Nasalsack theory, the latter is the more detailed and the most probable. Thus, the process of sound generation is as follows: toothed whales ( Odontoceti ) produce sounds with a complex of vocal folds ( phonic lips ) and fat- filled sacs ( bursae posteriorly ), which is located in the nasal passages or the vicinity thereof. The sound thus produced is fed into the melon, a high-fat body to the upper jaw bone that caused rounding of the end of toothed whales. It focuses the sound. There are two types of echolocation sounds: Whistling and non- whistling. Whistling - toothed whales emit rapid series of click -like, short and fast diminishing sounds of 40-70 microseconds duration, very high frequencies (in the harbor porpoise (Phocoena phocoena ), eg 120-145 kHz ) and up to 225 dB. Only very few species of toothed whales are non- whistling, so join the echolocation of 120-200 microseconds duration and often lower frequency than 10 kHz. The echo begins lack external ears on the rear part of the lower jaw. It transmits the sound to the adjacent middle and inner ear can perceive the frequencies over 100 kHz. Between the collection of sound and the excitement of the brainstem takes only 7-10 microseconds, for which an extremely fast nerve conduction ensures that the Zahnwalkopf exceeds the speed of conduction of a rat in spite of longer routes. Toothed whales do not have ears, but can still hear spatially, as they best achieved the echo of a lying directly in front of them the object and the sound beam is not homogeneous, external sound waves are so different nature than those in the center of the sound beam. In this way, follow toothed whales their prey, mostly fish. Range and accuracy of echolocation in toothed whales are only poorly explored: In experiments, bottlenose dolphins (Tursiops truncatus ) to 113 meters in 50 % of cases could detect an object. Toothed whales can determine most likely different species of fish from different directions correctly. Like bats fit toothed whales their calls to the distance to the prey; compared to bats their positioning signals, however, are generally much shorter in order to maintain high resolution in the high speed of sound in water.

Other

Some other groups of animals use simple forms of echolocation, including shrews, tenrecs, rats, the fat Schwalm ( Steatornis caripensis ) and some sailors, especially swiftlets. People can learn to orient themselves by echolocation ( Human echolocation ).

Counter-strategies of prey

To escape the echolocation by bats, insects evolved into at least six orders of the ability to perceive ultrasound, so they have the opportunity to escape from bats. This is done via the Tympanalorgan. Often there is a kind of evolutionary race for abilities to listen and discharging signals ( co-evolution ) - some tiger moths ( Arctiidae ) can even itself emit ultrasound to disturb bats in echolocation. Only a few fish is known that they perceive ultrasound and respond to him with escape, such as the alewife ( Alosa alosa ) and some other herring -like. For several herring -like this ability has been disproved experimentally.

Documents

• Zoology
• Underwater Sound