Bioacoustics

On cetaceans, acoustic communication has acquired a privileged position compared to other forms of communication; in fact, water, being far more denser than air, transmits sound efficiently while the light through it, it attenuated very quickly. Light propagates in water for only a few tens of meters, while the sounds reach much greater distances. All cetaceans emit sounds underwater.

The sound production is very varied, from a few tens of hertz songs of baleen whales, up to 150 kHz in echolocation pulses of the Delphinidae.

It differs from species to species, depending also on the utility of the sound emitted.

Generally, the sounds are divided into three categories and two acoustic functional categories.

The categories describe the acoustic spectral composition or sound quality and include:

• Clicks: impulsive sounds with a wide frequency band.

• Whistle: continuous sounds with a frequency usually not higher than 25 kHz, covering a distance of about 1-5 km. Typically, the whistles are often frequency modulated pure tones, band limited to medium-high (5-15Khz).

• Gusts pulse sound / burst pulsed sound: sequences of pulses very close together, so as to look like a single sound, often described with onomatopoeia words as squeack, buzz, groan.

 

bioacoustic

The functional categories are defined as echolocation or biosonar, by which the animal emits and receives its reflected sounds from the objects present in the environment. In recent years it has been recognized as the dolphins employ the biosonar for both perceptual  as well as social purposes; despite of this, we think the communication between dolphins is carried out primarily through the use of whistles and other less known vocalizations called in various ways: buzzes, barks, grunts and chirps. Caldwell & Caldwell (1968) have suggested that the stereotyped whistles of the bottlenose dolphin (Tursiops truncatus) had the function of "signature" and would identify individuals within a herd. Despite this hypothesis was later reaffirmed, over the years other studies have reported the absence of the signature whistle and have shown that dolphins, like other species, produce a predominant whistle that is shared by multiple individuals and that probably contains individual variables in acoustic parameters.

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