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

• Published in: Animal Behaviour
• Main Authors: Martin, Morgan Jennifer, Elwen, Simon Harvey, Kassanjee, Reshma, Gridley, Tess
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2019
• Subjects: Narrowband high-frequency (NBHF); Acoustics; Behaviour; Biosonar; Communication; Echolocation; Fast click series; Foraging; Clicks; Odontocetes; Vocalizations; Kayak; toothed whales
• Online Access: http://hdl.handle.net/2263/71067; https://doi.org/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 125 kHz. 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. Supplementary material: Video S1. A group of Heaviside's dolphins socializing at the study site, Shearwater Bay, ...