Abstract
Blue whale sound production has been thought to occur by Helmholtz resonance via air flowing from the lungs into the upper respiratory spaces. This implies that the frequency of blue whale vocalizations might be directly proportional to the size of their sound-producing organs. Here we present a sound production mechanism where the fundamental and overtone frequencies of blue whale B calls can be well modeled using a series of short-duration (<1 s) wavelets. We propose that the likely source of these wavelets are pneumatic pulses caused by opening and closing of respiratory valves during air recirculation between the lungs and laryngeal sac. This vocal production model is similar to those proposed for humpback whales, where valve open/closure and vocal fold oscillation is passively driven by airflow between the lungs and upper respiratory spaces, and implies call frequencies could be actively changed by the animal to center fundamental tones at different frequency bands during the call series.
Highlights
Over the last three decades, significant progress has been made in quantifying the signal characteristics and global variation of low-frequency sounds produced by blue whales, Balaenoptera musculus spp[1,2,3,4,5]
Many questions exist with regards to the physics of baleen whale sound production mechanisms
Aroyan et al.[18] proposed that blue whales produce sound by a monopole source oscillation of an air-filled cavity, and the animal’s anatomy suggest that calls are due to Helmholtz resonance, which allows for efficient constant frequency sound production over changing depths
Summary
Blue whales have a distinctive call repertoire, with significant variability among populations. The primary energy source to cause airflow over a cavity or chamber would be the change in pressure produced as the animal rises and descends in the water column as it provides the volume displacements needed to produce the B call[3, 18]. It is generally assumed no air escapes from baleen whales during sound production[23] because this would imply that water could enter the respiratory system and eliminate the whales’ ability to make the observed call series. Air flow rates have been estimated at 25–50 l/s based on resonance quality factors and duration of B calls[18]
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