Bioacoustics

Bioacoustics is a cross-disciplinary science that combines biology and acoustics. It can refer to the investigation of sound production and reception in animals, including humans. In underwater acoustics and fisheries acoustics the term is also used to mean the effect of plants and animals on sound.

Bioacoustics includes the study of the biological acoustically-borne information transfer and its propagation in elastic media. The term also refers to the organs of hearing and to the sound production apparatus, as well as to the physiological and neurophysiological processes by which sounds are produced, received and processed. Furthermore, bioacoustics attempts to understand the relationships between the features of the sounds an animal produces and the nature of the environment in which they are used, as well as the functions they are designed to serve. Finally, it includes the techniques associated with instrumental and biological sonar for its use in population monitoring, identification and communication encoding mechanisms and allows the assessment and control of the effects of human-made noise on animals. Source: Laboratory of Applied Bioacoustics

Some animals use sound ranging from infrasounds to ultrasounds to send messages to conspecifics. Basic messages are for calling mates (sexual calls), warning about a danger (alarm calls) or to intimidate a competitor (aggressive calls). In birds and mammals more complex messages can be broadcast. Some animals can also investigate the surrounding environment by emitting sounds and listening for returning echoes. Bats and dolphins have developed the most advanced echolocation capabilities to avoid obstacles and to find prey. They use short ultrasonic signals to reveal small objects (the shorter the wavelength, the smaller the objects that can be detected). The bat sounds are not audible to the human ear. This ability is also called "bio-sonar" or biological sonar. A special branch of bioacoustics, closely related to underwater acoustics, concerns the underwater world and marine mammals in particular.

Bioacoustics was established by the Slovenian biologist Ivan Regen.[1] 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 microphone and cricket females in front of a loudspeaker. The females were not moving towards the male but towards the loudspeaker.[2]

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

Marine bioacoustics

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.

Vertical, or down-looking sonar has become increasingly important to the assessment of marine fish, anadromous and land-locked salmonids (Thorne 1971, 1979; Burczynski and Johnson 1986; Mulligan and Kieser 1986; Levy et al. 1991; Yule 1992; Parkinson et al. 1994; Beauchamp et al. 1997; Wanzenbock et al. 2003), and lake and reservoir fishes (Thorne 1983; Brandt et al. 1991; Degan and Wilson 1995; Vondracek and Degan 1995; Schael et al. 1995; Cyterski et al. 2003; Taylor et al. 2005).

Sonar provides a repeatable and non-invasive method of collecting high-resolution (sub-meter scale), continuous data along transects in three dimensions (MacLennan and Simmonds 1992). give a thorough introduction in the use of hydroacoustics for measuring fish abundances and distributions.

Sounds Produced by Marine Mammals

Marine mammals use sounds for a variety of different purposes, such as alerting others to the presence of danger, communicating the presence of food, a conspecific, or another animal, as well as communicating their position identity and territorial status. Furthermore, some cetaceans use echolocation sounds to detect the position of objects underwater, and analyse their characteristics, whether they’re obstacles, prey or one another.

Baleen Whales

Although there has been a lot of research into characteristics and functions of sounds produced by fin whales, humpback whales, and southern right whales, there is no standard classification for baleen whale sounds. This is because it is very difficult to study the context and functions of baleen whale sounds, due to the fact that baleen whales, unlike other marine mammals, are rarely held in captivity.

Bowhead Whale Most sounds produced by bowhead whales are frequency modulated (FM) between 50 abd 400 Hz and single-note tones last about one second. However some have been known to be as short as 0.4 seconds or as long as 3.7 seconds. Above 400 Hz, most have little or no energy, however some reach 1200 Hz. Sounds are also always slightly stronger in front of the animal than behind. Bowhead whales also produce a variety of non-vocal slap and blow sounds. There is not much concrete evidence in order to be able to associate certain sounds with certain kinds of behavior of bowhead whales. However, it appears that high-pitched sounds and pulsatile sounds tend to be proportionally more common where bowheads are socialising. There has been speculation that bowheads, like other southern right whales use FM upsweeps as means of communication. Bowhead calls have been recorded when a mother and calf rejoin. Other speculation suggests that reverberations of calls could provide other bowheads with information about ice conditions assist in navigation. Bowhead whales also »sing« during spring migration in northern Alaska. Most consist of one to three themes composed of repeated phrases, which consist of one to five notes. Song notes tend to be longer than call sounds, with a greater frequency range, and more AM and FM variation. Normally songs last about 1 minute, but songs can last from several minutes to several hours.

Right Whale There are three types of right whales, southern right whales, northern right whales and pygmy right whales. Southern right whales and northern right whales both use an "up" sound for long distance contact and bringing groups together. Evidence of this is that calls cease once groups join. It's a simple tonal FM upsweep at 50-200 Hz, and tends to last from 0.5 seconds to 1.5 seconds. In contrast, a "down" call is used to maintain contact acoustically but not physically. It's a low-frequency tonal FM downsweep which lasts about 0.5 to 1.5 seconds at 100-200 Hz. However there is less data available to investigate sounds made by northern right whales. Pygmy right whales are very different from the southern and northern right whales, and are not closely related to other right whales. They produce thump like sounds in pairs 0.5 seconds apart, consisting of a frequency downsweep from 90-135 Hz to about 60 Hz, each being 140-225ms long. They generally have a lower frequency than the sounds of southern and northern right whales.

Acoustic tags

In order to track the movements of fish, whales, etc an acoustic device may be attached to an animal that emits a pulse at intervals, possibly coded with depth information for example.

See also

• Animal communication
• Animal language
• Field recording
• Natural sounds
• Sonar
• Underwater acoustics
• Zoomusicology

External links

• Marine Bioacoustics Centre of the University of South Florida. Has fish sound recordings.
• Laboratory of Applied Bioacoustics
• The British Library Sound Archive has 150,000 recordings of over 10,000 species.
• International Bioacoustics Council links to many bioacoustics resources.
• Borror Laboratory of Bioacoustics at The Ohio State University has a large archive of animal sound recordings.
• Listen to Nature 400 examples of animal songs and calls
• Wildlife Sound Recording Society
• xeno canto :: songs and calls of over 2900 neotropical bird species on-line