Bioacoustics

Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion through elastic media, and reception in animals, including humans. This involves neurophysiological and anatomical basis of sound production and detection, and relation of acoustic signals to the medium they disperse through. The findings give us some evidence about the evolution of acoustic mechanisms, and from that, the evolution of animals that employ them.

In underwater acoustics and fisheries acoustics the term is also used to mean the effect of plants and animals on sound propagated underwater, usually in reference to the use of sonar technology for biomass estimation [Medwin H. & Clay C.S. (1998). "Fundamentals of Acoustical Oceanography", Academic Press] Simmonds J. & MacLennan D. (2005). "Fisheries Acoustics: Theory and Practice", second edition. Blackwell]

History

Man has for a long time employed animal sounds to recognise and find them. Bioacoustics as a scientific discipline was established by the Slovenian biologist Ivan Regen. On 31 August 1925 he used a special stridulatory device to play in a duet with an insect. Later he put a male cricket behind a microphone and female crickets in front of a loudspeaker. The females were not moving towards the male but towards the loudspeaker. [Kočar T. (2004). " [http://www.gea-on.net/clanek.asp?ID=522 Kot listja in kobilic] " ("As many as leaves and grasshoppers"). GEA, october 2004. Mladinska knjiga, Ljubljana sl icon]

The most recent advances in bioacoustics concern the relationships among the animals and their environment and the impact of anthropogenic noise.

Methods in bioacoustics

Listening is still one of the main methods used in bioacoustical research. Little is known about neuropyhsiological processes that play a role in production, detection and interpretation of sounds in animals, so animal behaviour and the signals themselves are used for gaining insight into these processes.

Acoustic signals

[
Spectrogram (above) and oscillogram (below) of the humpback whale's calls] An experienced observer can use animal sounds to recognize a "singing" animal species, its location and condition in nature. Investigation of animal sounds also includes signal recording with electronic recording equipment. Due to the wide range of signal properties and media they propagate through, specialized equipment may be required instead of the usual microphones, such as hydrophone (underwater sounds), ultrasound detector (very high-frequency sounds), or laser vibrometer (substrate-borne vibrational signals). Computers are used for storing and analysis of recorded sounds. Specialized sound-editing software is used for describing and sorting signals according to their intensity, frequency, duration and other parameters.

Animal sound collections, managed by museums of natural history and other institutions, are an important tool for systematic investigation of signals.

ound production, detection, and use in animals

Scientists in the field of bioacoustics are interested in anatomy and neurophysiology of organs involved in sound production and detection, including their shape, muscle action, and activity of neuronal networks involved. Of special interest is coding of signals with action potentials in the latter.

But since the methods used for neurophysiological research are still fairly complex and understanding of relevant processes is incomplete, more trivial methods are also used. Especially useful is observation of behavioural responses to acoustic signals. One of such is phonotaxy - directional movement towards the signal source. By observing response to well defined signals in controlled environment, we can gain insight into signal function, sensitivity of the hearing apparatus, noise filtering capability, etc.

Biomass estimation

Biomass estimation uses sonar to detect fish, etc. As the sound pulse travels through water it encounters objects that are of different density than the surrounding medium, such as fish, that reflect sound back toward the sound source. These echoes provide information on fish size, location, and abundance. The basic components of the scientific echo sounder hardware function is to transmit the sound, receive, filter and amplify, record, and analyze the echoes. While there are many manufacturers of commercially available »fish-finders«, quantitative analysis requires that measurements be made with calibrated echo sounder equipment, having high signal-to-noise ratios.

Animal sounds

Sounds used by animals that fall within the scope of bioacoustics include a wide range of frequencies and media, and are often not sound in the strict sense of the word, i.e. compression waves that propagate through air and are detectable by the human ear. Katydid crickets, for example, communicate by sounds with frequencies higher than 100 kHz, far into the ultrasound range. [Mason A.C., Morris G.K., Wall P. (1991): "High Ultrasonic Hearing and Tympanal Slit Function in Rainforest Katydids". Naturwissenschaften 78: 365-367.] Lower, but still in ultrasound, are sounds used by bats for echolocation. On the other side of the frequency spectrum are low frequency-vibrations, often not detected by hearing organs, but with other, less specialized sense organs. The examples include ground vibrations produced by elephants whose principal frequency component is around 15 Hz, and low- to medium-frequency substrate-borne vibrations used by most insect orders [Virant-Doberlet M. & Čokl A. (2004): "Vibrational communication in insects". Neotropical Entomology 33(2): 121-134] . Many animal sounds, however, do fall within the frequency range detectable by a human ear, between 50 and 15,000 Hz. Mechanisms for sound production and detection are just as diverse as the signals themselves.

ee also

* Acoustic ecology
* Acoustical oceanography
* Animal communication
* Animal language
* Biomusic
* Field recording
* Natural sounds
* Sonar
* Underwater acoustics
* Vocal learning
* Whale song
* Zoomusicology

External links

* [http://www.marine.usf.edu/bio/fishlab/research.htm Marine Bioacoustics Centre] of the University of South Florida. Has fish sound recordings.
* [http://www.lab.upc.es/ Laboratory of Applied Bioacoustics]
* [http://www.bl.uk/collections/sound-archive/wild.html The British Library Sound Archive] has 150,000 recordings of over 10,000 species.
* [http://www.ibac.info/ International Bioacoustics Council] links to many bioacoustics resources.
* [http://blb.biosci.ohio-state.edu/ Borror Laboratory of Bioacoustics] at The Ohio State University has a large archive of animal sound recordings.
* [http://www.bl.uk/listentonature Listen to Nature] 400 examples of animal songs and calls
* [http://www.wildlife-sound.org/ Wildlife Sound Recording Society]
* [http://www.xeno-canto.org xeno canto :: songs and calls of over 4000 bird species from the Americas, Africa and Asia on-line]
* [http://beamreach.org Beam Reach Marine Science and Sustainability School] Killer whale sounds, some localized using hydrophone arrays
* [http://www.birds.cornell.edu/brp/?lk=lpro/ Bioacoustic Research Program] at the Cornell Lab of Ornithology distributes a number of different free bioacoustics synthesis & analysis programs.
* [http://www.birds.cornell.edu/macaulaylibrary/?lk=lpro Macaulay Library] at the Cornell Lab of Ornithology is the world's largest collection of animal sounds and associated video.
* [http://www.avisoft.com/ Avisoft Bioacoustics] provides various hardware and software solutions for bioacoustic research.

References

Further reading

* Ewing A.W. (1989): "Arthropod bioacoustics: Neurobiology and behaviour". Edinburgh: Edinburgh Universitsy Press. ISBN 0-7486-0148-1
* Fletcher N. (2007): " [http://www.springer.com/cda/content/document/cda_downloaddocument/sample%20chapter.pdf?SGWID=0-0-45-279393-p123153395 Animal Bioacoustics] ". IN: Rossing T.D. (ed.): " [http://www.springer.com/east/home/generic/search/results?SGWID=5-40109-22-153743469-0 Springer Handbook of Acoustics] ", Springer. ISBN 978-0-387-33633-6