with research on the larynx or syrinx. In humans, the vocal tract plays a far
more critical role in speech than does the larynx, and thus we have a
detailed understanding of the anatomy and physiology of the human vocal
tract and accurate quantitative models of its acoustics at rest and in motion.
Thus, compared to our knowledge of the human vocal tract, research on
animal vocal tract acoustics and dynamics is in its infancy, and information
on comparative anatomy of the vocal tract is scattered throughout works
focusing on digestion or respiration. Even the most basic questions have
been addressed for only a few species. However, despite a long pause in
publications since the late 1960s (Greenewalt 1968; Lieberman 1968;
Lieberman et al. 1969), there appears to be a growing realization of the
importance of the vocal tract in sound production in birds and mammals,
especially in the last decade (Suthers and Fattu 1973; Andrew 1976; Nowicki
1987; Hartley and Suthers 1988; Suthers and Hector 1988; Suthers et al.
1988; Owren and Bernacki 1988, 1998; Owren 1990; Hausberger et al. 1991;
Hauser 1992; Hauser et al. 1993; Westneat et al. 1993; Hauser and SchönYbarra 1994; Fitch 1994, 1997, 1999, 2000b, 2000c; Fitch and Hauser 1995;
Rendall 1996; Owren et al. 1997; Riede and Fitch 1999; Fitch and Reby
2001).
For anurans, the role of supralaryngeal filtering is more difficult to assess,
at least in part because of the pervasive use of the term “dominant frequency.” In anuran bioacoustics, dominant frequency refers to the highestamplitude frequency in the spectrum of a call, without regard to whether
this is the fundamental frequency, one of its harmonics, a noise- or impulseexcited formant, or a carrier frequency with amplitude-modulation sidebands. Although this term is convenient for acoustic analyses, it obscures
the important differences among such acoustic features, both in terms of
understanding vocal production and possibly in perception as well. For
example, many anuran vocalizations possess features that superficially
resemble formants, with a high-amplitude peak at one of the higher harmonics of a series. However, the data of Rand and Dudley (1993) suggest
that, at least for the four species they examined, this peak does not represent a formant frequency because the location of the highest-amplitude
spectral peak did not change in a helium/oxygen atmosphere (see Section
2.1.4). Such spectral peaks could be caused by low-frequency amplitude
modulation (e.g., by the arytenoids) of a higher carrier frequency (e.g., from
the vocal cords), as suggested by Schneider (1988) and Ryan (1985). Alternatively, they could result from an interaction between a generalized
descending spectral envelope (i.e., the -6 dB/octave amplitude drop-off
characteristic of most vocal sources) and impedance characteristics of the
frog’s body (where low frequencies are radiated poorly due to small body
sizes; see Section 2.2.5 below). Our point here is that the abundant and
excellent work in anuran bioacoustics could be more easily integrated into
the rest of bioacoustics (including work on humans, other mammals, and
birds) if explicit production-related terminology were adopted (e.g., sepa3. Unpacking “Honesty”
81
more critical role in speech than does the larynx, and thus we have a
detailed understanding of the anatomy and physiology of the human vocal
tract and accurate quantitative models of its acoustics at rest and in motion.
Thus, compared to our knowledge of the human vocal tract, research on
animal vocal tract acoustics and dynamics is in its infancy, and information
on comparative anatomy of the vocal tract is scattered throughout works
focusing on digestion or respiration. Even the most basic questions have
been addressed for only a few species. However, despite a long pause in
publications since the late 1960s (Greenewalt 1968; Lieberman 1968;
Lieberman et al. 1969), there appears to be a growing realization of the
importance of the vocal tract in sound production in birds and mammals,
especially in the last decade (Suthers and Fattu 1973; Andrew 1976; Nowicki
1987; Hartley and Suthers 1988; Suthers and Hector 1988; Suthers et al.
1988; Owren and Bernacki 1988, 1998; Owren 1990; Hausberger et al. 1991;
Hauser 1992; Hauser et al. 1993; Westneat et al. 1993; Hauser and SchönYbarra 1994; Fitch 1994, 1997, 1999, 2000b, 2000c; Fitch and Hauser 1995;
Rendall 1996; Owren et al. 1997; Riede and Fitch 1999; Fitch and Reby
2001).
For anurans, the role of supralaryngeal filtering is more difficult to assess,
at least in part because of the pervasive use of the term “dominant frequency.” In anuran bioacoustics, dominant frequency refers to the highestamplitude frequency in the spectrum of a call, without regard to whether
this is the fundamental frequency, one of its harmonics, a noise- or impulseexcited formant, or a carrier frequency with amplitude-modulation sidebands. Although this term is convenient for acoustic analyses, it obscures
the important differences among such acoustic features, both in terms of
understanding vocal production and possibly in perception as well. For
example, many anuran vocalizations possess features that superficially
resemble formants, with a high-amplitude peak at one of the higher harmonics of a series. However, the data of Rand and Dudley (1993) suggest
that, at least for the four species they examined, this peak does not represent a formant frequency because the location of the highest-amplitude
spectral peak did not change in a helium/oxygen atmosphere (see Section
2.1.4). Such spectral peaks could be caused by low-frequency amplitude
modulation (e.g., by the arytenoids) of a higher carrier frequency (e.g., from
the vocal cords), as suggested by Schneider (1988) and Ryan (1985). Alternatively, they could result from an interaction between a generalized
descending spectral envelope (i.e., the -6 dB/octave amplitude drop-off
characteristic of most vocal sources) and impedance characteristics of the
frog’s body (where low frequencies are radiated poorly due to small body
sizes; see Section 2.2.5 below). Our point here is that the abundant and
excellent work in anuran bioacoustics could be more easily integrated into
the rest of bioacoustics (including work on humans, other mammals, and
birds) if explicit production-related terminology were adopted (e.g., sepa3. Unpacking “Honesty”
81