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Russian researchers have recorded the sounds audible only inside the right part of the dolphin’s nasal passage. Animals produce them during echolocation. This research can shed light on how the cetacea produce ultrasonic signals.
Researchers of the Severtsov Institute of Ecology and Evolution Problems, Russian Academy of Sciences, have obtained the confirmation of the hypothesis that the cetacea, dolphins in particular, produce sounds with the help of some pneumatic mechanism, i.e. by driving air under pressure in the depths of the organism. It is assumed that the animals’ right nasal passage is involved in the production of sounds.
The point is that dolphins turn out to be capable of producing special internal sounds but the sounds can be heard only during echolocation. These sounds are called “internal” as they are not heard on the outside (the researchers have managed to make out the sounds only with the help of special internal sensors). They can be heard only in a single location – in the right part of the dolphin’s nasal passage. According to the researchers, these sounds resemble whistle or meowing. The frequency and other properties of these sounds differ significantly from the so-called communicating whistle with the help of which dolphins communicate with each other.
Apparently, dolphins do not produce these sounds on purpose. There exist two versions of their origin: probably they accompany the process of overblowing the air in the organs responsible for production of ultrasonic signals. Or perhaps, internal sounds “result” from pressure difference in various parts of the nasal passage when the air goes through of them. This version is also confirmed by measuring air pressure in the dolphins’ respiratory system.
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