Sperm Whale's chronicles

Vocalisation: “Using a Radar and Socialising”

Sperm whales are massive click producers and almost all the sounds heard from them are clicks [6]. Vocalisations are the way to communicate with one another and to “see” the environment, but also a way that scientists found to study their behaviour and populations [6].

Sperms’ clicks are directional and impulsive vocalisations with energy between 5 and 25 kHz [6] and the pulse is so strong that produces a sound pressure that you can feel as a punch (Video 1). Some believe that these pulses are strong enough to paralyse their prey (Video 2).

Sperm whales can use different patterns of vocalisation in different circumstances. The two main broad classes of function are clicks for echolocation (usual click and creak) and communication (coda and slow) [6].

Usual Click: high directionality, searching echolocation

Creak: high directionality, homing echolocation

Coda: low directionality, social communication

Slow:  low directionality, communication by males

Whitehead (2003) [6] describes a hypothesis in which clicks are made before the sperm find its target. Once it finds a target, it begins to creak, an appropriated approach for an animal hunting its target. This behaviour is consistent with the hypothesis in which clicks and creaks are used in echolocation.

Sperm whales are usually silent for long time when alone or resting or even socialising near of surface [6]. But it is not unusual to hear solitary males clicking while foraging. By the way, adult males’ clicks are usually associated with foraging, not with socialising [6].

Studies have shown that squids are poor targets for echolocation [6], which means that a strong signal is required to detect them. Therefore, the clicks of a sperm whale are loud. In fact, louder clicks lead to a strong echolocation signal, a longer range and a more effective signal [6].

 But where are these clicks produced? How can they interpret the signal?

The production of the sound begins in the animal’s head (Fig. 1), where a pulse of sound is produced by air being forced through the phonic lips [6]. This pulse will pass through the spermaceti organ, reflected and amplified by the junk into the ocean [6]. The vibration returned is received and conducted by tubes present in the lower jaw, than reaches the ear and is processed by the brain (Video 3).

Figure 1: Sperm whale’s head. The sound production begins in the phonic lips, passing through the spermaceti organ and junk. The reception of the sound occurs into the lower jaw, which transfers the sound to the inner ear.

A sperm whale may produce half a billion clicks during its life [6]. These clicks are fundamental for echolocation and communication in scales of meters and tens of kilometres [6]. Summarising, the spermaceti organ is the especial feature that enhances the sperm whale’s sensory of the ocean and makes it different from the other odontocetes.

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