242
D.L. Herzing
well as extract, important information through the use of aerial behaviors,
percussive sounds associated with body and tail movements underwater,
and species- and movement-specific information from prey, conspecifics, or
allospecifics as documented in bats (Kober 1988; von der Emde 1988).
3.8 Vocalizations Associated with Foraging and Feeding
Predominant vocalizations produced during hunting and foraging behavior
are echolocation clicks. S. frontalis and T. truncatus echolocate while scanning and digging for buried prey in sandy bottoms, increasing the repetition rate of clicks (from 200 to 500 clicks per second) as they direct their
sound into the sand. Bottom fish appear to be disoriented or stunned as
they emerged from the sand and become easy prey for the dolphins. T. truncatus use an echolocation train termed the "razor buzz" (aurally distinguishable from other echolocation click trains by the intensity and "tinny"
quality), ranging from 2.0 to 6.0kHz with repetition rates up to 200 clicks
per second (Herzing 1996). T. truncatus also use the razor buzz in conjunction with trills (repetitive series of discrete beeps below 5.0kHz) and
upswept whistles (ranged from 4.8 to 16.0kHz) during "ledge" feeding,
although these may serve another functions such as conspecific or coordination vocalizations. In addition, dolphins use jaw claps and open-mouth
scanning during hunting and foraging behavior.
Food preferences and hunting strategies have been obtained primarily
from sampling stomach content and from observations of surface behavior
including fish kicking (dos Santos and Lacerda 1987; Wells et aI. 1987) and
stranding on mud flats to retrieve fish (Hoese 1971; Rigley 1983). The use
of echolocation signals in the detection and retrieval of prey is well established, and intense sound pressure levels of over 220 dB re 11lPa (Au et aI.
1978, Au 1993) emitted by T. truncatus may have an effect on prey species
(Norris and Ml/Ihl 1981), although it has not been experimentally demonstrated. It should be noted that high-frequency echolocation clicks are very
directional (lOa from mid-line) and the maximum frequency recorded
during these underwater behaviors may be a limitation of recording equipment and the lack of ability to sample in front of the scanning dolphins.
Preliminary evidence that S. frontalis use clicks up to 140kHz and 210dB
re 11lPa has also been documented (Au et aI. 1998).
3.9 Acoustic Characteristics of Social Sounds
Relative to Hearing
A summary of both Table 5.2 and Figure 5.1 indicate that dolphin social
signals share some structural traits that may both relate to their function
and show conservation during the evolution of communication signals
across species. Sounds with sharp onset and energy emphasis in the lower
D.L. Herzing
well as extract, important information through the use of aerial behaviors,
percussive sounds associated with body and tail movements underwater,
and species- and movement-specific information from prey, conspecifics, or
allospecifics as documented in bats (Kober 1988; von der Emde 1988).
3.8 Vocalizations Associated with Foraging and Feeding
Predominant vocalizations produced during hunting and foraging behavior
are echolocation clicks. S. frontalis and T. truncatus echolocate while scanning and digging for buried prey in sandy bottoms, increasing the repetition rate of clicks (from 200 to 500 clicks per second) as they direct their
sound into the sand. Bottom fish appear to be disoriented or stunned as
they emerged from the sand and become easy prey for the dolphins. T. truncatus use an echolocation train termed the "razor buzz" (aurally distinguishable from other echolocation click trains by the intensity and "tinny"
quality), ranging from 2.0 to 6.0kHz with repetition rates up to 200 clicks
per second (Herzing 1996). T. truncatus also use the razor buzz in conjunction with trills (repetitive series of discrete beeps below 5.0kHz) and
upswept whistles (ranged from 4.8 to 16.0kHz) during "ledge" feeding,
although these may serve another functions such as conspecific or coordination vocalizations. In addition, dolphins use jaw claps and open-mouth
scanning during hunting and foraging behavior.
Food preferences and hunting strategies have been obtained primarily
from sampling stomach content and from observations of surface behavior
including fish kicking (dos Santos and Lacerda 1987; Wells et aI. 1987) and
stranding on mud flats to retrieve fish (Hoese 1971; Rigley 1983). The use
of echolocation signals in the detection and retrieval of prey is well established, and intense sound pressure levels of over 220 dB re 11lPa (Au et aI.
1978, Au 1993) emitted by T. truncatus may have an effect on prey species
(Norris and Ml/Ihl 1981), although it has not been experimentally demonstrated. It should be noted that high-frequency echolocation clicks are very
directional (lOa from mid-line) and the maximum frequency recorded
during these underwater behaviors may be a limitation of recording equipment and the lack of ability to sample in front of the scanning dolphins.
Preliminary evidence that S. frontalis use clicks up to 140kHz and 210dB
re 11lPa has also been documented (Au et aI. 1998).
3.9 Acoustic Characteristics of Social Sounds
Relative to Hearing
A summary of both Table 5.2 and Figure 5.1 indicate that dolphin social
signals share some structural traits that may both relate to their function
and show conservation during the evolution of communication signals
across species. Sounds with sharp onset and energy emphasis in the lower