Echolocation (animals)

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Exemplary representatives of echolocating groups of animals. Clockwise: Townsend long-eared long-eared ( Corynorhinus townsendii ), bottlenose dolphin ( Tursiops truncatus ), great tenrek ( Tenrec ecaudatus ), black- nest salangan ( Aerodramus maximus )

Echolocation in animals , also known as biosonar , is a special form of echolocation used by animals . It is used to orient an animal in space by actively emitting sound waves and then picking up and evaluating the echo. This ability is particularly pronounced in bats , which locate insects in this way, as well as in toothed whales , which use echolocation to track fish. Echolocation is found in a primitive form in some insectivores and birds. Echolocation enables orientation in low-light living spaces or at night.

Research history

The Italian Lazzaro Spallanzani observed in 1793 that bats can orient themselves in the dark even with their eyes gouged out, and the Swiss Louis Jurine experimentally proved in 1794 that bats with ears sealed with wax are disoriented in the dark. Both postulated a connection between orientation at night and the sense of hearing, but Georges Cuvier's public doubts soon made their theses forgotten. From 1938 the scientists Donald R. Griffin , George W. Pierce and Robert Galambos began to study the orientation of bats in the dark. Newly developed piezoelectric crystals , with the help of which ultrasound can be converted into frequencies that humans can hear, proved decisive in their investigations . Griffin and his colleagues explained the location mechanism and coined the term echolocation . Echolocation in toothed whales was first suspected in 1947 and confirmed experimentally in 1960.

General

Scheme of an echolocating bat

All echolocating animals use the same principle: They send out sound waves, these are reflected by objects in the vicinity and the echo is picked up by the ear. The brain processes the information into an image of the environment and determines the relative position of the animal to surrounding objects. For this purpose, mostly high-frequency sounds , often in the ultrasound , are used, as these are reflected back by small objects due to their short wavelength and enable a higher resolution. An echolocation 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 moves at the speed of sound ( ) - the animal can deduce the distance to the object from the difference in time between the emission of the sound signal and the arrival of the echo ( ) :

The localization of the direction ( direction of the auditory event ) is determined by spatial hearing without emitting sound waves. The procedure here differs from animal group to animal group.
Echolocation, on the other hand, requires a very fast conduction of excitation in the nervous system , since an echolocating animal has to process numerous signals in a short time and precise time differences are necessary for the precise determination of distances.

The echolocation developed independently of each other ( convergent ) in several animal groups . Although they use different organ systems for this purpose, there is a strong similarity in the protein prestin of toothed whales and bats , despite only a distant relationship . Prestin is responsible for the sensitivity and adaptation to certain frequencies of the ear.

Echolocation systems

Bats

Spectrogram : calls of a pipistrelle bat ( Pipistrellus pipistrellus ) during the hunt. Immediately (150  milliseconds ) before the prey contact, the call interval and duration are greatly reduced (" feeding buzz "). The main frequency of the calls is typically around 45 kHz for this type. The associated recording, stretched 20 times, can be listened to as an audio file:
Locating calls from a pipistrelle bat with a clearly recognizable echo . With each successive call, the distance between signal and echo is shortened.
The calls of bats are mostly in the ultrasound range and are therefore inaudible to humans. Here they were converted to lower frequencies with the help of a time-stretching bat detector .

Bats (Microchiroptera) generate locating sounds in the larynx in the frequency range of 8–160 kHz, depending on the species  . These mostly leave the body through the mouth opening, but in some groups such as the horseshoe bat (Rhinolophidae) through the nose. In such bats, special protrusions on the nose focus the sound. To catch the echo, bats have a sophisticated ear and large auricles. The vertical orientation of the object to the bat is determined by the bats either through interference caused by the tragus or through the independent raising and lowering of the auricles. Bats determine the horizontal origin of the echo from the difference in arrival and signal strength between the two ears. Bats adapt their location calls to the distance of their prey: In order to discover distant prey, they emit narrow-band (low-frequency), long tones. In the vicinity, broadband calls (containing many frequencies) lasting less than 5  ms are used, which enable very precise localization. Bats that modulate frequency in this way are called FM bats ( frequency modulated ). Some bats only use constant frequencies, they are classified as CF ( constant frequency ). The bats' middle ear muscle contracts when they call - so bats have to keep their calls short. Otherwise the middle ear muscle would still be tense when the echo arrives, so the bat would be deaf. In many species, echolocation is so well developed that the size and nature of prey can be determined very precisely. Some species can determine the distance very precisely by distinguishing between times of apparently only 10–12  ns . Echolocation bats develop a spatial memory through echolocation over time. So you have a three-dimensional picture of your living space "in your head" and can use it to orient yourself, even if you do not emit location sounds.

In the closely related flying foxes (Megachiroptera) only the species group of rosette bats has the ability to echolocate. These flying foxes do not produce their sounds in the larynx, but use their tongues to generate clicks of 0.6–1 ms duration and frequencies of 12–70 kHz.

Toothed whales

Section through the head of a toothed whale (here a dolphin)

There are several theories about sound generation in toothed whales. Up to now none has been fully confirmed. The most important theories about the generation of sound and its transmission into the water are the larynx theory and the nasal sac theory, the latter being the more detailed and probably the most likely. The process of sound generation is as follows: Toothed whales (Odontoceti) generate sounds with a complex of vocal folds ( phonic lips ) and fat-filled sacs ( dorsal bursae ), which are located in or near the nasal passages. The sound generated in this way is directed into the melon , a fatty organ above the upper jawbone that causes toothed whales to round their foreheads. 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 rapidly decreasing sounds of 40–70  µs duration, very high frequencies (in the harbor porpoise ( Phocoena phocoena ) e.g. 120–145 kHz) and up to 225  dB . Very few toothed whale species are non-whistling , which means that they emit sounds of 120–200 µs duration and often less than 10 kHz to locate them. Due to the lack of auricles, the echo picks up the rear part of the lower jaw. It transfers the sound to the adjacent middle and inner ear , which can perceive frequencies of over 100 kHz. Only 7–10 µs pass between the reception of the sound and the excitation of the brainstem, which is ensured by an extremely fast nerve conduction, which, despite the longer distances in the whale tooth, exceeds the speed of the conduction of excitation in a rat. Toothed whales have no auricles, but can still hear spatially because they best reach the echo of an object directly in front of them and the sound beam is not homogeneous, i.e. external sound waves are different from those in the center of the sound beam. This is how toothed whales pursue their prey, mostly fish. The range and accuracy of echolocation in toothed whales have only been poorly researched: In experiments, bottlenose dolphins ( Tursiops truncatus ) detected an object at a distance of 113 m in 50% of cases. Also, toothed whales can most likely correctly identify different species of fish from different directions. Like bats, toothed whales adapt their calls to the distance from the prey; Compared to bats, however, their location signals are generally much shorter in order to maintain a high resolution at the high speed of sound in water.

Other animals

An American shrew Blarina brevicauda with poor eyesight and smell, which uses ultrasound to orient itself.

Some other animal groups use simple forms of echolocation, including shrews (genera Sorex and Blarina ), tenreks , rats , slit weevils ( Solenodon ), the fat swallow ( Steatornis caripensis ) and some sailors , especially salangans , who often spend the night in dark caves.

Compared to bats, the ultrasonic sounds of shrews are quieter, multi-harmonic and use a broader spectrum. They are also frequency modulated. Shrews can only orient themselves in this way at close range.

Many animal species communicate in the ultrasound range, but do not seem to use their hearing for echolocation. Mice, for example, hear tones in the spectrum up to 100 kHz.

Humans can also learn to orientate themselves through echolocation ( human echolocation ).

Counter-strategies of prey animals

In order to avoid echolocation by bats, at least six orders of the insects developed the ability to perceive ultrasound, which gives them the opportunity to flee from bats. This is done through the tympanic organ . Often there is a kind of evolutionary race for abilities to hear and emit signals ( coevolution ) - some bear moths (Arctiidae) can even emit ultrasound themselves to disrupt the echolocation of bats. Only a few fish are known to sense ultrasound and react to it by fleeing, e.g. B. the allis shad ( Alosa alosa ) and some other herring species . However, this ability has been experimentally refuted for several species of herring.

supporting documents

  1. ↑ a b c d e f g h G. Jones: Echolocation. In: Current Biology. 15 (13), 2005, pp. 484-488.
  2. ↑ a b W. WL Au: Echolocation. In: WF Perrin, B. Wursig, JGM Thewissen (Ed.): Encyclopedia of Marine Mammals. 2nd Edition. Academic Press, 2008, ISBN 978-0-12-373553-9 , pp. 348-349.
  3. ^ Y. Li, Z. Liu, P. Shi, J. Zhang: The hearing gene Prestin unites echolocating bats and whales. In: Current Biology. 20 (2), 2010, pp. 55-56.
  4. ↑ a b c E. Kulzer: Chiroptera, Fledertiere (fruit bats and bats). In: W. Westheide, R. Rieger (Ed.): Special Zoology Part 2: Vertebrate or skull animals. Spektrum Akademischer Verlag, 2004, ISBN 3-8274-0307-3 , pp. 575-585.
  5. ↑ M. Ulanovsky, CF Moss: What the bat's voice tells the bat's brain. In: PNAS. 105 (25), 2008, pp. 8491-8498.
  6. ^ RA Holland, DA Waters, JMV Rayner: Echolocation signal structure in the Megachiropteran bat Rousettus aegyptiacus Geoffroy 1810. In: The Journal of Experimental Biology. 207, 2004, pp. 4361-4369.
  7. ^ AS Frankel: Sound Production. In: WF Perrin, B. Wursig, JGM Thewissen (Ed.): Encyclopedia of Marine Mammals. 2nd Edition. Academic Press, 2008, ISBN 978-0-12-373553-9 , pp. 1057-1071.
  8. ^ Y. Yovel, WWL Au: How Can Dolphins Recognize Fish According to Their Echoes? A Statistical Analysis of Fish Echoes. In: PLoS ONE. 5 (11), 2010, p. E14054. doi: 10.1371 / journal.pone.0014054 .
  9. ^ TE Tomasi: Echolocation by the Short-Tailed Shrew Blarina brevicauda . In: Journal of Mammalogy . 60, No. 4, 1979, pp. 751-9. doi : 10.2307 / 1380190 . , JSTOR 1380190
  10. ^ BM Siemers, G. Schauermann, H. Turni, S. Von Merten: Why do shrews twitter? Communication or simple echo-based orientation . In: Biology Letters . 5, No. 5, 2009, pp. 593-596. doi : 10.1098 / rsbl.2009.0378 . PMID 19535367 . PMC 2781971 (free full text).
  11. ^ M. Wilson, HB Schack, PT Madsen, A. Surlykke, M. Wahlberg: Directional escape behavior in allis shad (Alosa alosa) exposed to ultrasonic clicks mimicking an approaching toothed whale. In: The Journal of Experimental Biology. 214, 2011, pp. 22-29.