Nasal sound production in echolocating delphinids (Tursiops truncatus and Pseudorca crassidens) is dynamic, but unilateral: clicking on the right side and whistling on the left side

Abstract

SUMMARYToothed whales produce sound in their nasal complex by pneumatic actuation of phonic lip pairs within the blowhole. It has been hypothesized that dual actuation of the phonic lip pairs can generate two pulses that merge to form a single echolocation click with a higher source level, broader bandwidth and larger potential for beam steering than if produced by a single pair of phonic lips. Here, we test that hypothesis by measuring the sound production of five echolocating delphinids using hydrophones around the animals and imbedded in on-animal suction cups. We show that the studied animals click with their right pair of phonic lips and whistle with their left pair. We demonstrate that, with just a single pair of phonic lips, they can change the click energy levels over five orders of magnitude, change the click centroid frequencies over more than two octaves, and modulate the sound radiation from the melon for beam steering. We conclude that all of the click dynamics ascribed to dual actuation of two phonic lip pairs can be achieved with actuation of just the right pair of phonic lips, and we propose that the large dynamic range of source outputs is achieved by highly controlled modulation of the pneumatic driving pressure, the tension of the phonic lip labia and the conformation of the fatty melon and associated air sacs.

Amazon river dolphins (Inia geoffrensis) use a high-frequency short-range biosonar

“…Changing the SL is not without consequences and may lead to alterations of the frequency content of emitted clicks as decreases in SL correlates with decreases in F c (Moore and Pawloski, 1990;Au et al, 1995;Madsen et al, 2013a). The frequency content is important because directivity of a sonar beam follows the relationship between wavelength and effective aperture of the sound emitter, so for a constant melon size the DI will decrease with decreasing frequency (Au, 1993;Zimmer et al, 2005;Madsen and Wahlberg, 2007).…”

“…Theoretically, the best way a river dolphin can deal with clutter is by a downregulation of SL in conjunction with an ability to increase directivity, thus reducing detection range and decreasing beamwidth. However, an intricate relationship exists among SL, directivity and frequency (Moore and Pawloski, 1990;Au et al, 1995;Madsen et al, 2013a), so adjustments of one parameter are likely to affect the others. Depending on which parameters, or combinations thereof, are selected for over time, more than one evolutionary outcome may be possible for a clutter-adapted biosonar.…”

“…This would simplify the auditory scene through a decreased sensory volume, and provide high update rates, which we hypothesise are important when navigating a complex habitat. However, clicking at low SL has been shown to decrease the peak (F p ) and centroid frequency (F c ) of emitted clicks, thus lowering the DI (Houser et al, 2005;Madsen et al, 2013a). A low DI will provide more clutter, thus complicating echo processing.…”

False killer whale and short-finned pilot whale acoustic identification

“…Au et al 1995, Madsen et al 2004, Ibsen et al 2011 and false killer whale echolocation capabilities have mainly been studied with captive animals (e.g. Thomas & Turl 1990, Brill et al 1992, Yuen et al 2005, Kloepper et al 2012, Madsen et al 2013). The overall spectral content of their clicks seems to be generally lower than what is known for most other echolocating delphinids, having considerable energy below 20 kHz.…”

Comparative anatomical study of sound production and reception systems in the common dolphin (Delphinus delphis) and the harbour porpoise (Phocoena phocoena) heads

“…The harbour porpoise, which emits only clicks, has a symmetrical melon not directly linked to the source of the soundwave emission, although it has a clear asymmetry of the vestibular sacs (right sac larger, Huggenberger et al, 2009). The clicks are produced with the right organs (Hermann, 1980;Madsen, Lammers, Wisniewska, & Beedholm, 2013). The harbour porpoise which uses only clicks should develop more the right respiratory system (organs responsible of the clicks production).…”