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T.W. Cranford
addressed in his model. If there were some demonstrable negative effects
of interference generally, we should see the effects of selection against it
applied across all odontocetes in the form of atrophy and asymmetry. This
is not the case however, we have already discussed the "symmetrical" configuration in the phocoenid nasal apparatus and its possible function. These
are intriguing issues, and distilling conclusions from complicated methods
or results is always a treacherous undertaking. Aroyan's clever application
of numerical techniques points out their usefulness in posing questions and
narrowing the possible answers to others in future investigations..
Simultaneous production of whistles and clicks in a single animal has
been reported many times over the years (Lilly and Miller 1961; Evans and
Prescott 1962; Lilly 1962; Brill et al. 1992). Lilly (1962) suggested that dolphins may produce these sounds from different sides of the head (whistles
on the right and pulses on the left). Several intriguing questions remain.
Are dolphins and other nonphyseterid odontocetes limited to two (simultaneous) sound sources? If there are two sources, one associated with both
nasal passages, can they be pressurized independently and separately controlled by muscle action? Can clicks and whistles be produced on the same
side simultaneously? Answers to questions such as these should allow us to
set limits on the potential flexibility and ecological implications of the sound
generation system.
6.1.4 Mechanisms for Controlling Air Flow
The mechanism of odontocete sound generation is pneumatically driven, as
shown by several studies (Norris et al. 1971; Hollien et al. 1976; Ridgway
et al. 1980; Amundin and Andersen 1983; Ridgway and Carder 1988;
Cranford et al. 1997). Unfortunately, we can only surmise the importance
of mechanisms for precisely controlling the magnitude and direction of
air flowing to the phonic lips. How is force imparted to the flowing air
stream, and how is air directed to specific locations? How flexible or labile
are these mechanisms?
Perhaps nothing has been quite so intriguing as the brief glimpses
through an endoscope of activities that could provide answers to these
questions. We need to measure the pressure in various parts of the nasal
passages and correlate those measurements to the characteristics and
timing of the pulses that are generated. We should also investigate the structure and function of those curious furrows that form in the nasal mucosa.
Tissues that determine airflow characteristics are central to understanding
the dynamics of sonar signal generation and, as far as I know, are new subjects for study.
6.1.5 Cavitation
The possible involvement of cavitation in the sound generation mechanism
is another intriguing issue that deserves greater investigative attention. It
is possible that better physiologic time resolution using ultra-high-speed
T.W. Cranford
addressed in his model. If there were some demonstrable negative effects
of interference generally, we should see the effects of selection against it
applied across all odontocetes in the form of atrophy and asymmetry. This
is not the case however, we have already discussed the "symmetrical" configuration in the phocoenid nasal apparatus and its possible function. These
are intriguing issues, and distilling conclusions from complicated methods
or results is always a treacherous undertaking. Aroyan's clever application
of numerical techniques points out their usefulness in posing questions and
narrowing the possible answers to others in future investigations..
Simultaneous production of whistles and clicks in a single animal has
been reported many times over the years (Lilly and Miller 1961; Evans and
Prescott 1962; Lilly 1962; Brill et al. 1992). Lilly (1962) suggested that dolphins may produce these sounds from different sides of the head (whistles
on the right and pulses on the left). Several intriguing questions remain.
Are dolphins and other nonphyseterid odontocetes limited to two (simultaneous) sound sources? If there are two sources, one associated with both
nasal passages, can they be pressurized independently and separately controlled by muscle action? Can clicks and whistles be produced on the same
side simultaneously? Answers to questions such as these should allow us to
set limits on the potential flexibility and ecological implications of the sound
generation system.
6.1.4 Mechanisms for Controlling Air Flow
The mechanism of odontocete sound generation is pneumatically driven, as
shown by several studies (Norris et al. 1971; Hollien et al. 1976; Ridgway
et al. 1980; Amundin and Andersen 1983; Ridgway and Carder 1988;
Cranford et al. 1997). Unfortunately, we can only surmise the importance
of mechanisms for precisely controlling the magnitude and direction of
air flowing to the phonic lips. How is force imparted to the flowing air
stream, and how is air directed to specific locations? How flexible or labile
are these mechanisms?
Perhaps nothing has been quite so intriguing as the brief glimpses
through an endoscope of activities that could provide answers to these
questions. We need to measure the pressure in various parts of the nasal
passages and correlate those measurements to the characteristics and
timing of the pulses that are generated. We should also investigate the structure and function of those curious furrows that form in the nasal mucosa.
Tissues that determine airflow characteristics are central to understanding
the dynamics of sonar signal generation and, as far as I know, are new subjects for study.
6.1.5 Cavitation
The possible involvement of cavitation in the sound generation mechanism
is another intriguing issue that deserves greater investigative attention. It
is possible that better physiologic time resolution using ultra-high-speed