Università degli Studi di Pavia

Centro Interdisciplinare di Bioacustica e Ricerche Ambientali

The voices of marine mammals of the Mediterranean Sea

Odontocetes

Stenella coeruleoalba

The striped dolphin, while is a widespread species, it is not well studied for its acoustic features yet. It mostly produces high frequency whistles that may extend from few kHz to more than 20 kHz, with duration normally below 1 second, and echolocation clicks with energy peak among 50 and 150 kHz. It can produce whistles and clicks at the same time. It also emits series of clicks at high rates, called “bursts”, that appear tonal to the human ear. In literature the most varied names are given to these sounds: howling, meows, etc. Recent studies, still in progress, reveal that acoustic activity is significantly greater at night, when a category of impulsive sounds, called “castanets”, predominates on the other signals. The castanetses are rarely present in the daytime; it is believed that this acoustic behaviour is part of a hunting strategy to find food.

Recording of whistles from a group of striped dolphins. Whistles from different animals overlap, though it is possible to see repeated shapes probably emitted by a same individual. Arrows indicate two bursts of clicks.
S_coeruleoalba_whistles.wav (6.2MB) S_coeruleoalba_whistles_short.wav (570kB)
S_coeruleoalba_whistles.mp3 (1.1MB) S_coeruleoalba_whistles_short.mp3 (105kB)

Wide band recording of striped dolphins. Thin vertical lines are the spectrographic image of the clicks; on the left two bursts, that are very fast click series, are shown; on the right, whistles of at least two individuals overlap (other weak whistles of far animals are also shown).
Horizontal thin lines are electronic interferences, spots in the circles are due to the ship’s echosounder.

Tursiops truncatus

The bottlenose dolphin can be easily maintained in captivity and thus it has been studied for decades and, because of its learning abilities and vocal behaviours, it has become the prototype of the studies on the possible communication man-dolphin. It is also the species in which ecolochation capabilities are better known, therefore it represents the paradigm through which the other species are studied.
It can emit a large variety of signals, it is able to imitate sounds that it listens and to learn to use sounds for specific situations.
Wild animals have a large repertoire too; it produces whistles modulated in frequency among few kHz and over 20 kHz, fast series of clicks, and echolocation clicks. In its repertoire there is also the "jaw-clap" (a clapping sound produced by shutting the jaw), an impulsive sound that seems a shot, often called "gun-shot". T_truncatus_bang.wav (500kB) T_truncatus_bang.mp3 (86kB)

Bottlenose dolphin’s whistles. T_truncatus_whistles.wav (1.6MB) T_truncatus_whistles_short.wav (600kB)
T_truncatus_whistles.mp3 (287kB) T_truncatus_whistles_short.mp3 (105kB)

Fast click trains emitted by a bottlenose dolphin with a repetition rate of many hundreds of clicks per second. The human ear perceives these as tonal sounds that resembles meows and squeaks. Arrows indicate two “jaw-claps”. T_truncatus_buzzes.wav (800kB) T_truncatus_buzzes.mp3 (147kB)

Delphinus delphis

The acoustic behaviour of common dolphins is not well known, though it is very similar to that of the striped dolphins, with frequency modulated whistles ranging to more than 20 kHz and echolocation clicks.
The available knowledge does not allow discriminating common dolphins and striped dolphins with acoustic cues only.

Whistles and clicks emitted by common dolphins. D_delphis.wav (2.5MB) D_delphis.mp3 (456kB)

Grampus griseus

Risso’s dolphin mostly produces echolocation clicks and more rarely short whistles. Clicks emitted at high rates, other than for echolocation purposes, are likely used for communication. Such high rate click series sound like tonals to the human ear.

Trains of clicks emitted with a repetition rate of tens per second; the human ear perceives them as a raspberry. G_griseus.wav (6.2MB) G_griseus_short.wav (400kB) G_griseus.mp3 (1.1MB) G_griseus_short.mp3 (103kB)

Fast click series from a Risso’s dolphin.

Globicephala melas

Long finned pilot whales emit modulated low frequency whistles rarely exceeding 5 - 8 kHz and clicks. The firsts are believed to be social signals, while the seconds are very likely biosonar pulses for echolocation purposes.

Pilot whales’ whistles. The fundamental frequency of whistles is normally below 5 kHz.
G_melas.wav (1MB) G_melas.mp3 (196kB)

Pilot whales whistles and clicks.

Steno bredanensis

This species is poorly studied and few recordings are known. The only taken in the Mediterranean Sea, taped in 1957 by Bill Watkins, shows clicks and simple whistles with few modulations but frequency shifts. Frequencies are normally below 17 kHz.

Recording made by Bill Watkins (WHOI, Woods Hole Oceanographic Institution, USA) in Mediterranean waters.

Ziphius cavirostris

In the last 10 years attention focused on this species, and on beaked whales in general, because of their repeated presence in mass strandings occurred in concomitance with military sonar exercises. Even if the causes of the strandings are not completely determined, it is clear the connection with acoustic issues. The Cuvier’s beaked whale’s acoustic behaviour is still mostly unknown and a few hypotheses and datasets are today under discussion. In particular it would be important too know the sounds they emit to possibly detect their presence in areas to be used for sonar exercises.
The team of Woods Hole Oceanographic Institutions is currently investigating on the diving and vocal behaviour of this species by attaching (with suction caps) an acoustic recorder on its back. According to data published by the WHOI team the Ziphius emits echolocation clicks centered on 40 kHz with about 400 msec of inter click interval (ICI) when it is diving at depth greater than 400-500 meters. This could explain why those clicks have never been recorded with hydrophones close to the surface.

Phocena phocena

The harbour porpoise is the smallest dolphin inhabiting the Mediterranean – Black Sea system. This species is mainly studied in the North Sea waters because of the interaction with fisheries. It produces narrow band echolocation clicks at about 140 kHz.

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Created June 2005, updated August 2005