48
D.R. Ketten
ducers that coincide with the two suborders. Odontocetes are fundamentally high-frequency animals and mysticetes are low-frequency animals.
3.1 Odontocete Acoustic Categories
Odontocetes produce multiple signal types including species-stereotypic
broadband echolocation clicks with peak energy between 10 and 200kHz,
individually variable burst pulse click trains, and constant frequency (CF)
or frequency modulated (FM) whistles ranging from 4 to 16 kHz (Tyack and
Clark, Chapter 4). Ultrasonic signals have been recorded from 21 species,
although echolocation (or "biosonar") has been demonstrated unequivocally in only 11 species of smaller odontocetes (Au, Chapter 9). All modern
odontocetes are assumed, like bats, to be true echolocators, not simply ultrasonic receptors; that is, they "image' their environment by analyzing echoes
from a self-generated ultrasonic signal. Captive odontocetes vary pulse repetition rate, interpulse interval, intensity, and click spectra, particularly in
response to high ambient noise, but in general, each odontocete species has
a characteristic echolocation frequency spectrum (Watkins and Wartzok
1985). Peak spectra of odontocete sonar signals range from approximately
16 kHz in the killer whale (Orcinus orca) to over 130 kHz in the harbor porpoise (P. phocoena) with typical source levels of 150 to 170dB although
level estimates as high as 230dB have been reported (Au 1993).
The functional significance of species differences in the spectra of natural
echolocation signals has not been directly tested, but there are strong correlations with habitat types and peak spectra (Ketten and Wartzok 1990).
Two acoustic categories were established for odontocetes based on the peak
frequency at maximum energy of common ultrasonic signals (Ketten 1984):
Type I with peak spectra above 100kHz and Type II with peak spectra
below 100kHz (Tables 2.1 and 2.2). Because frequency and wavelength are
inversely related, these types also imply differences in the size of the objects
or details detected through echolocation. Type I echolocators tend to be
near-shore and riverine species that operate in relatively low-light, acoustically complex waters. For example, the South American boutu (Inia geoffrensis) routinely hunts small fish amidst the roots and stems choking silted
Amazonian "varzea" lakes and produces signals up to 200kHz (Norris et
al. 1972). A second Type I species, the harbor porpoise (P. phocoena), inhabits near-shore waters and shallow seas in colder latitudes and typically uses
110 to 140kHz signals (Kamminga 1988). Communication signals are rare
(or are rarely observed) in most Type I species (Watkins and Wartzok 1985),
and, as discussed below, their auditory systems are dominated by ultra-highfrequency adaptations. Type II species are primarily delphinids, which ~re
near- and offshore animals that inhabit low object density environments,
generally travel in large pods, are highly social, and employ lower ultrasonic
frequencies with longer wavelengths that are consistent with detecting
larger objects over greater distances. They also devote substantial acoustic
D.R. Ketten
ducers that coincide with the two suborders. Odontocetes are fundamentally high-frequency animals and mysticetes are low-frequency animals.
3.1 Odontocete Acoustic Categories
Odontocetes produce multiple signal types including species-stereotypic
broadband echolocation clicks with peak energy between 10 and 200kHz,
individually variable burst pulse click trains, and constant frequency (CF)
or frequency modulated (FM) whistles ranging from 4 to 16 kHz (Tyack and
Clark, Chapter 4). Ultrasonic signals have been recorded from 21 species,
although echolocation (or "biosonar") has been demonstrated unequivocally in only 11 species of smaller odontocetes (Au, Chapter 9). All modern
odontocetes are assumed, like bats, to be true echolocators, not simply ultrasonic receptors; that is, they "image' their environment by analyzing echoes
from a self-generated ultrasonic signal. Captive odontocetes vary pulse repetition rate, interpulse interval, intensity, and click spectra, particularly in
response to high ambient noise, but in general, each odontocete species has
a characteristic echolocation frequency spectrum (Watkins and Wartzok
1985). Peak spectra of odontocete sonar signals range from approximately
16 kHz in the killer whale (Orcinus orca) to over 130 kHz in the harbor porpoise (P. phocoena) with typical source levels of 150 to 170dB although
level estimates as high as 230dB have been reported (Au 1993).
The functional significance of species differences in the spectra of natural
echolocation signals has not been directly tested, but there are strong correlations with habitat types and peak spectra (Ketten and Wartzok 1990).
Two acoustic categories were established for odontocetes based on the peak
frequency at maximum energy of common ultrasonic signals (Ketten 1984):
Type I with peak spectra above 100kHz and Type II with peak spectra
below 100kHz (Tables 2.1 and 2.2). Because frequency and wavelength are
inversely related, these types also imply differences in the size of the objects
or details detected through echolocation. Type I echolocators tend to be
near-shore and riverine species that operate in relatively low-light, acoustically complex waters. For example, the South American boutu (Inia geoffrensis) routinely hunts small fish amidst the roots and stems choking silted
Amazonian "varzea" lakes and produces signals up to 200kHz (Norris et
al. 1972). A second Type I species, the harbor porpoise (P. phocoena), inhabits near-shore waters and shallow seas in colder latitudes and typically uses
110 to 140kHz signals (Kamminga 1988). Communication signals are rare
(or are rarely observed) in most Type I species (Watkins and Wartzok 1985),
and, as discussed below, their auditory systems are dominated by ultra-highfrequency adaptations. Type II species are primarily delphinids, which ~re
near- and offshore animals that inhabit low object density environments,
generally travel in large pods, are highly social, and employ lower ultrasonic
frequencies with longer wavelengths that are consistent with detecting
larger objects over greater distances. They also devote substantial acoustic