5. Acoustics and Social Behavior
237
should not discount the possibility that there are other social uses of
frequency-modulated whistles.
3.2 Vocalizations Associated with Excitement,
Distress, and Alarm
The "whistle-squawk" and sharp clicks are the predominate vocalizations
produced during behavioral contexts of alarm and distress. S. frontalis
produce an "excitement vocalization," a combination burst-pulsed sound
(in the lower 4 to 8 kHz range) and signature whistle of the vocalizer (8 to
18kHz). The duration of this vocalization ranges from 2 to 30s. During the
production of this vocalization, dolphins are highly erratic in their swimming behavior and emit a stream of bubbles. The trigger for distress behavior varies from intraspecific social behavior to the presence of human
observers in the water. After the production of the vocalization begins, a
conspecific makes tactile contact, after which the excitement vocalization
ceases. Although counterintuitive, this vocalization has not been observed
in the presense of a predator such as a shark. Instead, there is some degree
of urgency when conspecifics calm down an excited cohort, indicating the
need to avoid broadcasting.
The excitement vocalization is similar in structure to the whistle-squawk
described by Caldwell and Caldwell (1967) who reported that T truncatus,
when removed from the water, emitted this vocalization. They suggested
that this type of sound is emitted when the dolphin is "protesting." This may
indicate that dolphins emit this sound when they are distressed, excited, or
have lost control of their vocalization apparatus during the production of
this type of combined sound. Reiss (1988) also reported the presence of
whistle-squawk for two infant T truncatus, and suggested that these sounds
are produced during emotional behavior.
Sharp clicks with rapid onset times, including nonvocal sounds such as
tail-slaps and even camera clicks from researchers, elicit startle responses
in S. frontalis. Dolphins are known to have an enhanced sensitivity to short
duration, rapid rise-time stimuli (Bullock et al. 1968; Bullock and Ridgway
1972). Dolphins are good at temporal and spatial resolution and are sensitive to small changes in intensity (Ralston and Herman 1989) indicating
that they may be very adept at deciphering incremental changes in both
time and intensity or amplitude of a signal. It is likely these skills are utilized in ambient noise and environmental assessment, but may also playa
role in deciphering social sounds of conspecifics.
The behavior of S. frontalis in the presence of sharks, a potentially alarming context, has rarely been observed. In the Bahamas, S. frontalis share
habitat with at least four major predatory sharks, and limited observations
over 12 years indicate that dolphins take different strategies according
237
should not discount the possibility that there are other social uses of
frequency-modulated whistles.
3.2 Vocalizations Associated with Excitement,
Distress, and Alarm
The "whistle-squawk" and sharp clicks are the predominate vocalizations
produced during behavioral contexts of alarm and distress. S. frontalis
produce an "excitement vocalization," a combination burst-pulsed sound
(in the lower 4 to 8 kHz range) and signature whistle of the vocalizer (8 to
18kHz). The duration of this vocalization ranges from 2 to 30s. During the
production of this vocalization, dolphins are highly erratic in their swimming behavior and emit a stream of bubbles. The trigger for distress behavior varies from intraspecific social behavior to the presence of human
observers in the water. After the production of the vocalization begins, a
conspecific makes tactile contact, after which the excitement vocalization
ceases. Although counterintuitive, this vocalization has not been observed
in the presense of a predator such as a shark. Instead, there is some degree
of urgency when conspecifics calm down an excited cohort, indicating the
need to avoid broadcasting.
The excitement vocalization is similar in structure to the whistle-squawk
described by Caldwell and Caldwell (1967) who reported that T truncatus,
when removed from the water, emitted this vocalization. They suggested
that this type of sound is emitted when the dolphin is "protesting." This may
indicate that dolphins emit this sound when they are distressed, excited, or
have lost control of their vocalization apparatus during the production of
this type of combined sound. Reiss (1988) also reported the presence of
whistle-squawk for two infant T truncatus, and suggested that these sounds
are produced during emotional behavior.
Sharp clicks with rapid onset times, including nonvocal sounds such as
tail-slaps and even camera clicks from researchers, elicit startle responses
in S. frontalis. Dolphins are known to have an enhanced sensitivity to short
duration, rapid rise-time stimuli (Bullock et al. 1968; Bullock and Ridgway
1972). Dolphins are good at temporal and spatial resolution and are sensitive to small changes in intensity (Ralston and Herman 1989) indicating
that they may be very adept at deciphering incremental changes in both
time and intensity or amplitude of a signal. It is likely these skills are utilized in ambient noise and environmental assessment, but may also playa
role in deciphering social sounds of conspecifics.
The behavior of S. frontalis in the presence of sharks, a potentially alarming context, has rarely been observed. In the Bahamas, S. frontalis share
habitat with at least four major predatory sharks, and limited observations
over 12 years indicate that dolphins take different strategies according