228
D.L. Herzing
S. frontalis, and T. truncatus, and perhaps other tropical and semitropical
species yet unexplored.
2. Historical Functional and Structural Classes of
Vocal Signals
Delphinid vocalizations have traditionally been divided up into three structural types-whistles, burst-pulsed vocalizations, and echolocation clicksand two functional categories-echolocation clicks used for orientation and
navigation and burst-pulsed sounds and frequency-modulated whistles used
for social signals.
Classification techniques of the vocal repertoire of dolphins have suffered from nomenclature difficulties. Inherent in call classification is the
lack of sufficient spectral and structural information to allow comparison
or consistency between research. Examples of some common names and
spectral features of the acoustic repetoire of selected species are given in
Table 5.2. The isolation of individual structural units of sound versus the
combined and sequential use between conspecifics also makes understanding the function of vocalizations, and subsequently hearing, difficult. The
repertoire of a species is usually viewed as a subset of sounds, with each
subset of sound varying over one or more dimensions or parameters such
as frequency contour, duration, etc. The lack of data on salient physical
and structural features of vocalzations, and contextual differences, makes
understanding the function of such communication signals challenging.
The relationship between basic behavioral categories and acoustic characteristics of social sounds can be seen in Fig. 5.l.
Frequency-modulated whistles have been extensively analyzed due to the
relative ease of analysis of their discrete features such as contour, frequency
modulation over time, duration, and peak frequency (see Caldwell et at.
1990). Whistles tend to be continuous, narrow-band signals with harmonic
features. Many whistles in the literature are described as being below
the 20 kHz level but this may be a function of limited bandwidth recording equipment. Although echolocation click studies have utilized instrumentation recorders to capture ultrasonic information, recent broadband
recording of the social sounds of S. longirostris have shown the existence
of information above 20kHz in both whistles and other social sounds
(Lammers and Au 1997).
Burst-pulsed sounds have been much neglected in the literature, although
they comprise the majority of conspecific vocalizations. Burst-pulsed
sounds are broadband, discrete aural packets of clicks and have acquired
descriptive names such as squawks, bleats, barks, etc. Spectral features of
burst-pulsed sounds have been anaylzed for a few species (Overstrom 1983;
Sjare and Smith 1986; Herzing 1988, 1996) but the nature of their informational content is largely unknown. Analyses have been particularly plagued
D.L. Herzing
S. frontalis, and T. truncatus, and perhaps other tropical and semitropical
species yet unexplored.
2. Historical Functional and Structural Classes of
Vocal Signals
Delphinid vocalizations have traditionally been divided up into three structural types-whistles, burst-pulsed vocalizations, and echolocation clicksand two functional categories-echolocation clicks used for orientation and
navigation and burst-pulsed sounds and frequency-modulated whistles used
for social signals.
Classification techniques of the vocal repertoire of dolphins have suffered from nomenclature difficulties. Inherent in call classification is the
lack of sufficient spectral and structural information to allow comparison
or consistency between research. Examples of some common names and
spectral features of the acoustic repetoire of selected species are given in
Table 5.2. The isolation of individual structural units of sound versus the
combined and sequential use between conspecifics also makes understanding the function of vocalizations, and subsequently hearing, difficult. The
repertoire of a species is usually viewed as a subset of sounds, with each
subset of sound varying over one or more dimensions or parameters such
as frequency contour, duration, etc. The lack of data on salient physical
and structural features of vocalzations, and contextual differences, makes
understanding the function of such communication signals challenging.
The relationship between basic behavioral categories and acoustic characteristics of social sounds can be seen in Fig. 5.l.
Frequency-modulated whistles have been extensively analyzed due to the
relative ease of analysis of their discrete features such as contour, frequency
modulation over time, duration, and peak frequency (see Caldwell et at.
1990). Whistles tend to be continuous, narrow-band signals with harmonic
features. Many whistles in the literature are described as being below
the 20 kHz level but this may be a function of limited bandwidth recording equipment. Although echolocation click studies have utilized instrumentation recorders to capture ultrasonic information, recent broadband
recording of the social sounds of S. longirostris have shown the existence
of information above 20kHz in both whistles and other social sounds
(Lammers and Au 1997).
Burst-pulsed sounds have been much neglected in the literature, although
they comprise the majority of conspecific vocalizations. Burst-pulsed
sounds are broadband, discrete aural packets of clicks and have acquired
descriptive names such as squawks, bleats, barks, etc. Spectral features of
burst-pulsed sounds have been anaylzed for a few species (Overstrom 1983;
Sjare and Smith 1986; Herzing 1988, 1996) but the nature of their informational content is largely unknown. Analyses have been particularly plagued