On doing two things at once: dolphin brain and nose coordinate sonar clicks, buzzes, and emotional squeals with social sounds during fish capture

Abstract

Dolphins fishing alone in open waters may whistle without interrupting their sonar clicks as they find and eat or reject fish. Our study is the first to match sound and video from the dolphin with sound and video from near the fish. During search and capture of fish, free-swimming dolphins carried cameras to record video and sound. A hydrophone in the far field near the fish also recorded sound. From these two perspectives, we studied the time course of dolphin sound production during fish capture. Our observations identify the instant of fish capture. There are three consistent acoustic phases: sonar clicks locate the fish; about 0.4 s before capture, the dolphin clicks become more rapid to form a second phase, the terminal buzz; at or just before capture, the buzz turns to an emotional squeal (the victory squeal), which may last 0.2 to 20 s after capture. The squeals are pulse bursts that vary in duration, peak frequency and amplitude. The victory squeal may be a reflection of emotion triggered by brain dopamine release. It may also affect prey to ease capture and/or it may be a way to communicate the presence of food to other dolphins. Dolphins also use whistles as communication or social sounds. Whistling during sonar clicking suggests that dolphins may be adept at doing two things at once. We know that dolphin brain hemispheres may sleep independently. Our results suggest that the two dolphin brain hemispheres may also act independently in communication.

Echolocation and burst clicks from franciscana dolphins (Pontoporia blainvillei) on the coast of Uruguay

“…Click train characteristics have been associated with foraging/feeding in bottlenose dolphin (Au 1993, Nowacek 2006, Jensen et al 2009, Ridgway et al 2015. Compared to Melcon et al (2012) who found abundant click production during feeding behavior, few click sounds were registered in this study.…”

Sensory Perception in Cetaceans: Part I—Current Knowledge about Dolphin Senses As a Representative Species

“…They are composed of two identical sound producing structures consisting of fatty dorsal bursae within a pair of phonic lips, one in the left and one in the right nasal passage (Cranford et al, 1996). A recent study suggested that the two dolphin brain hemispheres, which sleep independently (Lyamin et al, 2008), may also act independently when it comes to coordinating prey capture and communication with simultaneously emitted echolocation clicks and social sounds (Ridgway et al, 2015).…”

Sound Generating Structures of the Humpback Dolphin Sousa plumbea (Cuvier, 1829) and the Directionality in Dolphin Sounds

“…Experimental studies have demonstrated singularities on the sound emission of dolphins in which both echolocation and communication sounds are emitted simultaneously (Ridgway et al, ) and with specific source locations: the echolocation signals were produced in the right side of the epicranial complex, while the left side was used for communication sounds, such as whistles and pulsed calls (Madsen et al, ). Although, it has been demonstrated that the biosonar beam originates more or less at the center in T. truncatus (Moore et al, ; Finneran et al, ), the source center of the right sound beam may be adjusted by means of the mobility of the nasal plugs by retraction of the nasal plug muscles during vocalizing (Mead, ; Heyning and Mead, ).…”