The influence of air-filled structures on wave propagation and beam formation of a pygmy sperm whale (Kogia breviceps) in horizontal and vertical planes

Abstract

The wave propagation, sound field, and transmission beam pattern of a pygmy sperm whale (Kogia breviceps) were investigated in both the horizontal and vertical planes. Results suggested that the signals obtained at both planes were similarly characterized with a high peak frequency and a relatively narrow bandwidth, close to the ones recorded from live animals. The sound beam measured outside the head in the vertical plane was narrower than that of the horizontal one. Cases with different combinations of air-filled structures in both planes were used to study the respective roles in controlling wave propagation and beam formation. The wave propagations and beam patterns in the horizontal and vertical planes elucidated the important reflection effect of the spermaceti and vocal chambers on sound waves, which was highly significant in forming intensive forward sound beams. The air-filled structures, the forehead soft tissues and skull structures formed wave guides in these two planes for emitted sounds to propagate forward.

Evolution of cranial telescoping in echolocating whales (Cetacea: Odontoceti)

“…Beyond the bony anatomy, physeteroids also are the only living odontocetes to lack a melon, instead possessing a spermaceti organ, and uniquely retain distinct left and right nasal tracks that lead to a single blowhole (Cranford 1999;Heyning 1989). Studies of the roles of skull and soft tissues of Physeter (Huggenberger et al 2014;Song et al 2017) and Kogia (Karol et al 1978;Goold and Clarke 2000;Song et al 2015;Thornton et al 2015 suggest acoustic specializations linked to this unusual structure, but some of the unique cranial and soft tissue structures of the head of Physeter may be derived for ramming behaviors (Panagiotopoulou et al 2016;Alam et al 2016) as well. The bizarre cranial morphology described above has resulted in Kogia having a significant influence on the identification of major sources of variation in our facial morphology dataset; Kogia forms an extreme outlier for PC 4 of the whole skull dataset and principle components 3, 4, and 6 for the half skull dataset.…”

Bone-conducted sound in a dolphin's mandible: Experimental investigation of elastic waves mediating information on sound source position

“…Simple physical considerations suggest that anatomical features characterized by relatively strong density contrasts with respect to the surrounding medium (water) most significantly contribute to characterizing the HRTF, and thus to sound localization. Since the density of soft tissues found in marine mammal bodies is close to that of water (Norris and Harvey, 1974;Reysenbach de Haan, 1957), it is inferred that features such as the mandible, the cranium or small air sacs play the most important roles, similar to the external ears of terrestrial mammals (Aroyan et al, 1992;Song et al, 2017;Wei et al, 2016). One important difference in the sound localization performance of terrestrial mammals vs cetaceans is the latter's ability to localize sound sources within the median plane with a very high accuracy (Renaud and Popper, 1975).…”

Investigation on acoustic reception pathways in finless porpoise (Neophocaena asiaorientalis sunameri) with insight into an alternative pathway

“…Odontocetes have a remarkable capability to actively control produced sounds (Au 1993, Au andHastings 2008). This ability stems from their complex sound production and beam formation systems, which involve different sets of anatomical structures including the solid skull, fluid air components and soft tissues (Aroyan et al 1992, Cranford et al 1996, Song et al 2016, 2017b, Wei et al 2015, Zhang et al 2017. The combination of these structures forms a natural acoustic material, which provides a gradient of sound speeds and densities to efficiently influence echolocation beam formation (e.g.…”