To buzz or burst-pulse? The functional role of Heaviside's dolphin, Cephalorhynchus heavisidii, rapidly pulsed signals

• Published in: Animal behaviour Vol. 150; pp. 273 - 284
• Main Authors: Martin, Morgan J., Elwen, Simon H., Kassanjee, Reshma, Gridley, Tess
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.04.2019
• Subjects: acoustics; behaviour; biosonar; communication; echolocation; fast click series; foraging; narrowband high-frequency clicks; odontocetes; vocalizations; echolocation; fast click series; narrowband high-frequency clicks; acoustics; odontocetes; foraging; vocalizations; behaviour; communication; biosonar
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2019.01.007

Four groups of toothed whales have independently evolved to produce narrowband high-frequency (NBHF) echolocation signals (i.e. clicks) with a strikingly similar waveform and centroid frequency around 125kHz. These signals are thought to help NBHF species avoid predation by echolocating and communicating at frequencies inaudible to predators, a form of acoustic crypsis. Heaviside's dolphins produce NBHF echolocation clicks in trains and often in rapid succession in the form of buzzes. In addition, a second click type with a lower frequency and broader bandwidth was recently described, typically emitted in rapid succession in the form of burst-pulses. We investigated the relationship between buzz and burst-pulse signals and both surface behaviour (foraging, ‘interacting with the kayak’ and socializing) and group size, using a multivariable regression on the signal occurrence and signal count data. Signal occurrence and counts were not related to group size in the regression analysis. Burst-pulses were strongly linked to socializing behaviour, occurring more often and more frequently during socializing and much less during foraging. Buzz vocalizations were not strongly linked to a specific behaviour although there was some evidence of an increase in production during foraging and socializing. In addition, individual level production rates of buzzes during foraging and socializing, and burst-pulses during socializing decreased with increasing group size. Temporally patterned burst-pulse signals were also identified, often occurring within a series of burst-pulses and were directly linked to specific events such as aerial leaping, backflipping, tail slapping and potential mating. Our findings suggest Heaviside's dolphins have a more complex communication system based on pulsed vocalizations than previously understood, perhaps driven by the need to facilitate the social interactions of this species. •Acoustic and surface behaviour relationships were examined in Heaviside's dolphins.•Heaviside's dolphins produce burst-pulse signals most often when socializing.•Burst-pulse and buzz production per dolphin decreases with increasing group size.•Temporally patterned burst-pulses may imply underlying complexity in communication.