and the environments in which they principally live? Can this relationship
be used to predict the communicative functions of the different types of
signals produced?
There are only 11 recognized extant species in the baleen whale (Mysticeti) group (Ridgeway and Harrison 1985). All are known to produce
sounds, but representations of vocal repertoires are still incomplete for six
species (Thompson et al. 1979; Watkins and Wartzok 1985; Clark 1990;
Edds-Walton 1997). Full repertoires are available for five species: southern
and northern right whales, bowhead whale, gray whale, and humpback
whale (Clark 1982; Ljungblad et al. 1982; Tyack 1983; Clark and Johnson
1984; Dahlheim et al. 1984; Silber 1986; Chabot 1988). Good acoustic representations are available for the blue whale (Balaenoptera musculus), fin
whale (Balaenoptera physalus) (Cummings and Thompson 1971; Watkins et
al. 1987; Edds 1988; Thompson et al. 1992; Stafford 1999), and minke whale
(Balaenoptera acutorostrata) (Winn and Perkins 1976; Mellinger et al. 2000;
Edds-Walton 2000). There are a few sample recordings for Bryde’s (Balaenoptera edeni) (Cummings 1985; Edds et al. 1993), sei (Balaenoptera
borealis) (Thompson et al. 1979; Knowlton et al. 1991), and pygmy right
(Caperea marginata) (Dawbin and Cato 1992) whales.
Baleen whale sounds are often very intense, with maximum reported
band levels as high as 188 dB re 1 mPa (see Richardson et al. 1995, Table
7.1). Typical source levels range from 155 to 180 dB, but more research is
needed to document natural variability in source levels under different contexts (e.g., Thode et al. 2000). Increasing the source level is one direct mechanism for reaching a greater audience. This is especially true for deep-ocean
conditions where there are fewer surface and bottom reflections. However,
when water depth is poorly matched to a signal’s frequency band, the
energetic cost of increasing source intensity may outweigh the advantages
of increased communication range. Under such circumstances, selection
should favor changes in other signal characteristics (e.g., frequency band or
duration) to achieve greater communication range.
For purposes of this discussion, we refer to species that prefer coastal
and/or shallow water habitats during major portions of their lives as coastal
and species that spend major portions of their lives in deep water as pelagic.
In general, coastal species are easier to study, and more is known about
them, than pelagic species. All five species with essentially complete
acoustic repertoires are coastal. This includes the bowhead, northern right,
southern right, gray, and humpback whales. The southern right and bowhead whales are used as representative coastal species. The humpback
whale, a species more closely related to blue and fin whales than to right
whales, is also used as a coastal species while recognizing that it spends a
considerable portion of the year migrating across pelagic regions. All balaenopterid species spend a large proportion of their lives in the open ocean
and for this reason alone are difficult to study. With few exceptions,
the mating and calving areas and behaviors for these species are largely
36
A.H. Bass and C.W. Clark
be used to predict the communicative functions of the different types of
signals produced?
There are only 11 recognized extant species in the baleen whale (Mysticeti) group (Ridgeway and Harrison 1985). All are known to produce
sounds, but representations of vocal repertoires are still incomplete for six
species (Thompson et al. 1979; Watkins and Wartzok 1985; Clark 1990;
Edds-Walton 1997). Full repertoires are available for five species: southern
and northern right whales, bowhead whale, gray whale, and humpback
whale (Clark 1982; Ljungblad et al. 1982; Tyack 1983; Clark and Johnson
1984; Dahlheim et al. 1984; Silber 1986; Chabot 1988). Good acoustic representations are available for the blue whale (Balaenoptera musculus), fin
whale (Balaenoptera physalus) (Cummings and Thompson 1971; Watkins et
al. 1987; Edds 1988; Thompson et al. 1992; Stafford 1999), and minke whale
(Balaenoptera acutorostrata) (Winn and Perkins 1976; Mellinger et al. 2000;
Edds-Walton 2000). There are a few sample recordings for Bryde’s (Balaenoptera edeni) (Cummings 1985; Edds et al. 1993), sei (Balaenoptera
borealis) (Thompson et al. 1979; Knowlton et al. 1991), and pygmy right
(Caperea marginata) (Dawbin and Cato 1992) whales.
Baleen whale sounds are often very intense, with maximum reported
band levels as high as 188 dB re 1 mPa (see Richardson et al. 1995, Table
7.1). Typical source levels range from 155 to 180 dB, but more research is
needed to document natural variability in source levels under different contexts (e.g., Thode et al. 2000). Increasing the source level is one direct mechanism for reaching a greater audience. This is especially true for deep-ocean
conditions where there are fewer surface and bottom reflections. However,
when water depth is poorly matched to a signal’s frequency band, the
energetic cost of increasing source intensity may outweigh the advantages
of increased communication range. Under such circumstances, selection
should favor changes in other signal characteristics (e.g., frequency band or
duration) to achieve greater communication range.
For purposes of this discussion, we refer to species that prefer coastal
and/or shallow water habitats during major portions of their lives as coastal
and species that spend major portions of their lives in deep water as pelagic.
In general, coastal species are easier to study, and more is known about
them, than pelagic species. All five species with essentially complete
acoustic repertoires are coastal. This includes the bowhead, northern right,
southern right, gray, and humpback whales. The southern right and bowhead whales are used as representative coastal species. The humpback
whale, a species more closely related to blue and fin whales than to right
whales, is also used as a coastal species while recognizing that it spends a
considerable portion of the year migrating across pelagic regions. All balaenopterid species spend a large proportion of their lives in the open ocean
and for this reason alone are difficult to study. With few exceptions,
the mating and calving areas and behaviors for these species are largely
36
A.H. Bass and C.W. Clark