10
w.w.L. Au
4. Sound Emissions by Cetaceans
Odontocetes and mysticetes emit very different types of sounds. Many
odontocetes emit a variety of different types of sounds that are generally
categorized as whistles, burst pulses, and echolocation clicks. Some odontocetes such as P phocoena, C. commersonii, Cephalorhynclus hectori
(Hector's dolphin), Neophocaena phocaenoides (finless porpoise), Phocoenoides dalli (Dall's porpoise), and Kogia breviceps (pygmy sperm
whales) do not emit whistles but only burst pulses and echolocation clicks.
Odontocete sounds extend over a wide frequency range from about 5 kHz
to over 135 kHz, depending on the type of sounds and the species. Baleen
whales also emit a variety of sounds, most of which tend to be in the lowfrequency range extending from about 14Hz to about 5kHz, but typically
below 1kHz. Therefore it would not be surprising if odontocetes and mysticetes produce sounds in very different ways. Most of what we know of
sound production mechanisms comes from research with odontocetes. Very
little work has been done on sound production mechanism with baleen
whales. Aroyan et al. (Chapter 10) discuss a model of sound production in
blue whales.
4.1 Sound Production Mechanisms in Dolphins and
Small Whales
The general location of the sound production mechanism for dolphins was
once a relatively controversial issue. Cranford (Chapter 3) provides a
detailed discussion of this topic, including an interesting historical development in the understanding of the sound production mechanism in dolphins. The two most popular proposed sites were the larynx and the nasal
sac system. All of the measurement done with live phonating dolphins seem
to implicate the nasal sac area of the dolphin's head. Movements in the
nasal system that correlated with sound production have been observed by
many investigators, whereas such correlated movements in the larynx have
never been seen (Cranford, Chapter 3). Dormer (1979) observed that the
movement of the left nasal plug was associated with whistle production and
speculated that the right nasal plug was associated with click production.
Others (Ridgway et al. 1980; Mackay and Liaw 1981; Amundin and Andersen 1983) have found evidence of nasal plug movement, air sacs vibration,
and various muscle potential firing in the nasal area associated with sound
production. Pressure changes and muscle potential firing in the trachea
associated with sound production were never detected.
The proponents of a laryngeal sound production mechanism based their
arguments mainly on anatomical considerations and experiments with dead
animals (Lilly and Miller 1961; Purves 1967; Blevins and Parkins 1973;
Schenkkan 1973; Purves and Pilleri 1986). There is a complete lack of exper-
w.w.L. Au
4. Sound Emissions by Cetaceans
Odontocetes and mysticetes emit very different types of sounds. Many
odontocetes emit a variety of different types of sounds that are generally
categorized as whistles, burst pulses, and echolocation clicks. Some odontocetes such as P phocoena, C. commersonii, Cephalorhynclus hectori
(Hector's dolphin), Neophocaena phocaenoides (finless porpoise), Phocoenoides dalli (Dall's porpoise), and Kogia breviceps (pygmy sperm
whales) do not emit whistles but only burst pulses and echolocation clicks.
Odontocete sounds extend over a wide frequency range from about 5 kHz
to over 135 kHz, depending on the type of sounds and the species. Baleen
whales also emit a variety of sounds, most of which tend to be in the lowfrequency range extending from about 14Hz to about 5kHz, but typically
below 1kHz. Therefore it would not be surprising if odontocetes and mysticetes produce sounds in very different ways. Most of what we know of
sound production mechanisms comes from research with odontocetes. Very
little work has been done on sound production mechanism with baleen
whales. Aroyan et al. (Chapter 10) discuss a model of sound production in
blue whales.
4.1 Sound Production Mechanisms in Dolphins and
Small Whales
The general location of the sound production mechanism for dolphins was
once a relatively controversial issue. Cranford (Chapter 3) provides a
detailed discussion of this topic, including an interesting historical development in the understanding of the sound production mechanism in dolphins. The two most popular proposed sites were the larynx and the nasal
sac system. All of the measurement done with live phonating dolphins seem
to implicate the nasal sac area of the dolphin's head. Movements in the
nasal system that correlated with sound production have been observed by
many investigators, whereas such correlated movements in the larynx have
never been seen (Cranford, Chapter 3). Dormer (1979) observed that the
movement of the left nasal plug was associated with whistle production and
speculated that the right nasal plug was associated with click production.
Others (Ridgway et al. 1980; Mackay and Liaw 1981; Amundin and Andersen 1983) have found evidence of nasal plug movement, air sacs vibration,
and various muscle potential firing in the nasal area associated with sound
production. Pressure changes and muscle potential firing in the trachea
associated with sound production were never detected.
The proponents of a laryngeal sound production mechanism based their
arguments mainly on anatomical considerations and experiments with dead
animals (Lilly and Miller 1961; Purves 1967; Blevins and Parkins 1973;
Schenkkan 1973; Purves and Pilleri 1986). There is a complete lack of exper-