186
P.L. Tyack and c.w. Clark
specializations for sonar processing may have influenced the evolution of
auditory processing in these species.
The Phocoenid porpoises and dolphins of the genus Cephalorhynchus are
not known to produce any of the sounds typically associated with social
communication in other dolphins (Dawson and Thorpe 1990; Amundin
1991). The same clicks thought to be used for echolocation in these species
may also function in social communication (Dawson and Thorpe 1990;
Amundin 1991; Dawson 1991). Amundin (1991) associated relatively
stereotyped patterns of repetition rate of "echolocation" clicks with specific
social contexts in the harbor porpoise. Dawson (1991) also found that specific kinds of complex clicks in Hector's dolphin, C. hectori, were associated
with large groups and specific group activities. High repetition rates of
Hector's dolphin clicks were associated with aerial and aggressive behavioral contexts rather than feeding. If predators of these species, such as killer
whales, cannot hear the high frequencies of these clicks, then it may be
advantageous to use these high frequencies as a "private channel" for
communication as well as echolocation.
3.1.4 Sperm Whales
Just as with Phocoenids, the primary vocalizations reported from sperm
whales are clicks (Fig. 4.7). If sperm whales do produce tonal calls, they are
very rare. The rare reports of tonal sounds recorded near sperm whales
occurred when a calf was present (Gordon 1987, Watkins et aI.1988). Sperm
whale clicks are broadband clicks, ranging in frequency from several
hundred Hertz to tens of kiloHertz, with dominant frequencies often
around 2 to 4 kHz. The clicks recorded from sperm whales are made up of
a burst of pulses often reported to have very regular interpulse spacing (Fig.
4.8, from Backus and Schevill1962; see also Goold 1996). Most sperm whale
clicks have durations of several tens of milliseconds and are produced at
regular repetition rates typically of 0.5 to 2 clicks/second. These are called
"regular" clicks. Sperm whales also occasionally produce rapid bursts of
clicks, often referred to as "creaks" or "fast series," and rhythmic patterns
of clicks called "codas" (Watkins and Schevill 1977). Large male sperm
whales also produce longer clicks with an even longer interpulse interval
than regular clicks, earning these clicks the name "slow clicks" (Weilgart
and Whitehead 1988). The click on the left of Fig. 4.7 at 0.1 to 0.2 seconds
is a slow click and the other clicks to the right are regular clicks.
3.1.4.1 Functional Anatomy
Sperm whales devote an enormous fraction of their body volume to an
unusual organ called the spermaceti organ. The spermaceti organ lies dorsal
and anterior to the skull and can have a length up to 40% of the length of
the whale. Norris and Harvey (1972) suggest that the regular spacing of
pulses within sperm whale clicks may result from reverberation within the
P.L. Tyack and c.w. Clark
specializations for sonar processing may have influenced the evolution of
auditory processing in these species.
The Phocoenid porpoises and dolphins of the genus Cephalorhynchus are
not known to produce any of the sounds typically associated with social
communication in other dolphins (Dawson and Thorpe 1990; Amundin
1991). The same clicks thought to be used for echolocation in these species
may also function in social communication (Dawson and Thorpe 1990;
Amundin 1991; Dawson 1991). Amundin (1991) associated relatively
stereotyped patterns of repetition rate of "echolocation" clicks with specific
social contexts in the harbor porpoise. Dawson (1991) also found that specific kinds of complex clicks in Hector's dolphin, C. hectori, were associated
with large groups and specific group activities. High repetition rates of
Hector's dolphin clicks were associated with aerial and aggressive behavioral contexts rather than feeding. If predators of these species, such as killer
whales, cannot hear the high frequencies of these clicks, then it may be
advantageous to use these high frequencies as a "private channel" for
communication as well as echolocation.
3.1.4 Sperm Whales
Just as with Phocoenids, the primary vocalizations reported from sperm
whales are clicks (Fig. 4.7). If sperm whales do produce tonal calls, they are
very rare. The rare reports of tonal sounds recorded near sperm whales
occurred when a calf was present (Gordon 1987, Watkins et aI.1988). Sperm
whale clicks are broadband clicks, ranging in frequency from several
hundred Hertz to tens of kiloHertz, with dominant frequencies often
around 2 to 4 kHz. The clicks recorded from sperm whales are made up of
a burst of pulses often reported to have very regular interpulse spacing (Fig.
4.8, from Backus and Schevill1962; see also Goold 1996). Most sperm whale
clicks have durations of several tens of milliseconds and are produced at
regular repetition rates typically of 0.5 to 2 clicks/second. These are called
"regular" clicks. Sperm whales also occasionally produce rapid bursts of
clicks, often referred to as "creaks" or "fast series," and rhythmic patterns
of clicks called "codas" (Watkins and Schevill 1977). Large male sperm
whales also produce longer clicks with an even longer interpulse interval
than regular clicks, earning these clicks the name "slow clicks" (Weilgart
and Whitehead 1988). The click on the left of Fig. 4.7 at 0.1 to 0.2 seconds
is a slow click and the other clicks to the right are regular clicks.
3.1.4.1 Functional Anatomy
Sperm whales devote an enormous fraction of their body volume to an
unusual organ called the spermaceti organ. The spermaceti organ lies dorsal
and anterior to the skull and can have a length up to 40% of the length of
the whale. Norris and Harvey (1972) suggest that the regular spacing of
pulses within sperm whale clicks may result from reverberation within the