Bioacoustics is a cross-disciplinary science that combines biology and acoustics. Usually it refers to the investigation of sound production, dispersion and reception in (including humans).
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. Wiley-Blackwell] The study of substrate-borne vibrations used by animals is considered by some a distinct field called biotremology.
History
For a long time humans have employed animal sounds to recognise and find them. Bioacoustics as a scientific discipline was established by the
Slovenes biologist
Ivan Regen who began systematically to study
insect sounds. In 1925 he used a special
stridulation 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). Kot listja in kobilic ( As many as leaves and grasshoppers). GEA, October 2004. Mladinska knjiga, Ljubljana ] Regen's most important contribution to the field apart from realization that insects also detect airborne sounds was the discovery of
tympanal organ's function.
Relatively crude electro-mechanical devices available at the time (such as ) allowed only for crude appraisal of signal properties. More accurate measurements were made possible in the second half of the 20th century by advances in electronics and utilization of devices such as and digital recorders.
The most recent advances in bioacoustics concern the relationships among the animals and their acoustic environment and the impact of anthropogenic noise. Bioacoustic techniques have recently been proposed as a non-destructive method for estimating biodiversity of an area.
Importance
In the terrestrial environment, animals often use light for sensing distance, since light propagates well through air. Underwater sunlight only reaches to tens of meters depth. However, sound propagates readily through water and across considerable distances. Many marine animals can see well, but using hearing for communication, and sensing distance and location. Gauging the relative importance of audition versus vision in animals can be performed by comparing the number of
Auditory Nerve and
Optic nerve.
Since the 1950s to 1960s, studies on dolphin echolocation behavior using high frequency click sounds revealed that many different marine mammal species make sounds, which can be used to detect and identify species under water. Much research in bioacoustics has been funded by naval research organizations, as biological sound sources can interfere with military uses underwater.
Methods
Listening is still one of the main methods used in bioacoustical research. Little is known about neurophysiological processes that play a role in production, detection and interpretation of sounds in animals, so
ethology and the signals themselves are used for gaining insight into these processes.
Bioacoustics has also helped to pave the way for new emerging methods such as ecoacoustics (or acoustic ecology),
Acoustic signals
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
microphone, such as a
hydrophone (for underwater sounds), detectors of
ultrasound (very high-
frequency sounds) or
infrasound (very low-frequency sounds), or a laser vibrometer (substrate-borne vibrational signals).
are used for storing and analysis of recorded sounds. Specialized sound-editing
software is used for describing and sorting signals according to their
amplitude,
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. Many effective automated methods involving signal processing, data mining, machine learning and artificial intelligence[M. Pourhomayoun, P. Dugan, M. Popescu, and C. Clark, “Bioacoustic Signal Classification Based on Continuous Region Features, Grid Masking Features and Artificial Neural Network,” International Conference on Machine Learning (ICML), 2013.]
Sound production, detection, and use in animals
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
involved. Of special interest is coding of signals with
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 such response is phonotaxis – directional movement towards the signal source. By observing response to well defined signals in a controlled environment, we can gain insight into signal function, sensitivity of the hearing apparatus, noise filtering capability, etc.
Biomass estimation
Biomass estimation is a method of detecting and quantifying
fish and other marine organisms using
sonar technology.
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
calibration 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 narrow sense of the word (i.e.
that propagate through
air and are detectable by the human
ear).
Tettigoniidae, for example, communicate by sounds with frequencies higher than 100
Hertz, far into the ultrasound range.
Lower, but still in ultrasound, are sounds used by
for echolocation. A segmented marine worm
Leocratides kimuraorum produces one of the loudest popping sounds in the ocean at 157 dB, frequencies 1–100 kHz, similar to the
Alpheidae.
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.
Many animal sounds, however, do fall within the frequency range detectable by a human ear, between 20 and 20,000 Hz.
Mechanisms for sound production and detection are just as diverse as the signals themselves.
Plant sounds
In a series of scientific journal articles published between 2013 and 2016,
Monica Gagliano of the University of Western Australia extended the science to include plant bioacoustics.
See also
Further reading
External links
