Sperm whale acoustic

Physeter macrocephalus

Sperm whales emit signals called clicks, wideband and directional frequency, with power ranging between 5 and 25 kHz. These sounds are used for echolocation and for communication. The clicks can be very powerful, up to 223 dB re 1μPa / 1m, the most intense biological source than has ever been recorded.

 

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Normally, the sperm whale emits regular sequences of clicks (usual clicks) which are used to explore the environment in search of potential prey.

Sometimes the clicks change rhythm, speeding up to a range of 5 to 100 milliseconds from one click to another. In this case the vocalization is called creak and it can be emitted both in depth and on the surface.

During the immersion phase, the clicks acceleration is interpreted as an attempt of the sperm whale to focus on the identified prey and it is then used as an index of food activity.

Spectrogram  of usual clicks and creak of sperm whale recorded in the study area.

 

  

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The creaks emitted on the surface appear to have a shorter and a more consistent interval between clicks; depending on the authors, they have been defined tail-creaks or chirrups. It has been described as social sounds, but it’s not yet clear whether it’s used for echolocation or communication.

 

Spectrogram of tail-creaks sperm whale recorded in the study area.

 

Certainly the most interesting vocalization of this species it’s the so-called codas, stereotyped pattern of clicks, whose function may be communication through the patterns and rhythms of sequences of clicks.

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They seem to be signals used within groups for communicating between a group and another, in fact, they have a very low intensity emission.

Cultural transmission has recently been proposed for the codas: some social units share an acoustic repertoire (dialect) that allow us to classify them into the clan. Clans are sympatric (sharing the same territory),  they can contain thousands of sperm whales and be distributed in thousands of kilometers. The codas acoustic repertoire is culturally transmitted in the smallest form of the social structure of sperm whales, the social unit or family group composed of adult females and immature individuals of both sexes.

Spectrogram of sperm whale codas recorded in the study area

 

In the oceans several codas models have been recorded.  Some types of codas seem to be common to different areas and for a long time it was believed that the model 3 + 1 was the only type registered in the Mediterranean, even though, on a few occasions, other codas were recorded.  In the study area the codas model 3 + 1 is well represented, however, the presence of several different models, suggest a more varied repertoire.

Pure tones?

Although in the literature it is well documented, in general, it is considered that the vocalizations of sperm whale is restricted to clicks type signals but recent recordings suggest that sperm whales may issue other types of signals. In the study area these sounds were recorded in 2004, on the occasion of the presence of different social groups. In particular,  from the spectrograms comparison, these sounds appear to be similar to other recorded by Goold (1999) and Drouot (2003) and referred to as squeals, which are narrow-band sounds with modulated frequencies.

 

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The illustration shows a signal with a flat frequency harmonic structure. In some cases squeals have a decreased frequency in the final part.

The basic component of squeals was in the region of 7.5 kHz. The squeals analyzed vary in duration from approximately 0.3 seconds to 0.7 s, with a predominance of energy in the central and low harmonics.

 

Spectrogram of sperm whales squeal recorded in the study area.