Loud and clear: Characterization of particle motion in Humpback whale song and its potential role in communication

Abstract

Acoustic communication can rapidly transfer a substantial amount of information, yet emitted signals must be conveyed with enough clarity to allow appropriate responses. Many mysticete calls such as humpback whale (Megaptera novaeangliae) song can be detected over large distances as a result of the propagating acoustic pressure wave, yet little is known regarding the particle motion component of these signals. To explore the particle velocity of humpback whale song, three singing whales were recorded from a vessel off Maui, HI in March 2015, using a sensor that contained a digital magnetometer, tri-axial accelerometer, and an omnidirectional hydrophone. The median magnitude of the acoustic particle velocity signal was substantial (64.5 dB re: 1m/s) for song components with a median pressure of 135.4 dB re: 1μPa. As vessel and sensor gradually drifted away or toward the whales, acoustic particle velocity and sound pressure correspondingly decreased or increased (range: 49.3-77.9 dB re: 1m/s and 118.4-148.1 dB re: 1μPa). The particle velocity signals were high even at 200m from the whale indicating this cue is substantial well into the far-field. There were predictable trends in the acoustic particle motion signal component and this component of song is a cue available to nearby animals.