Inflation of the esophagus and vocal tract filtering in ring doves

Abstract

Ring doves vocalize with their beaks and nostrils closed, exhaling into inflatable chambers in the head and neck region. The source sound produced at the syrinx contains a fundamental frequency with prominent second and third harmonic overtones, but these harmonics are filtered out of the emitted signal. We show by cineradiography that the upper esophagus, oral and nasal cavities collect the expired air during vocalization and that the inflated esophagus becomes part of the suprasyringeal vocal tract. The level of the second and third harmonics, relative to the fundamental frequency (f 0 ), is reduced in the esophagus and emitted vocalization compared with in the trachea, although these harmonics are still considerably higher in the esophagus than in the emitted signal. When the esophagus is prevented from fully inflating, there is a pronounced increase in the level of higher harmonics in the emitted vocalization. Our data suggest that the trachea and esophagus act in series as acoustically separate compartments attenuating harmonics by different mechanisms. We hypothesize that the trachea behaves as a tube closed at the syringeal end and with a variable, restricted opening at the glottal end that lowers the tracheal first resonance to match the f 0 of the coo. The inflated esophagus may function as a Helmholtz resonator in which the elastic walls form the vibrating mass. Such a resonator could support the f 0 over a range of inflated volumes.

Songbirds tune their vocal tract to the fundamental frequency of their song

“…They also use expiratory pressure to passively inflate their esophagus, rather than active muscular tension (18). Furthermore, the resonance of the dove's filter is not critically dependent on the volume of the vocal tract, because there is a compensating effect on the physical properties of the esophageal wall (19,20). However, the most crucial difference is that although sound radiation from songbirds is through the partly open beak, sound radiation in doves occurs by mechanical vibration of the thin walls of the esophagus.…”

“…The center frequency of the first few of these resonances changes very little during song; this is consistent with measurements indicating that tracheal length changes very little during zebra finch song (22) and with the finding that changes in the beak gape of the eastern towhee have minimal effect on tracheal resonance (10). In theory, the resonances of the songbird tracheal filter could be lowered without changing tracheal length, by constricting the glottis (19). We are unaware of evidence that songbirds normally constrict their glottis during song, but the contribution of the glottis to the vocal tract filter remains to be explored.…”

“…X-ray imaging was performed with an x-ray unit having a mobile C-arm (Cardiac Digital Mobile Imaging System; Series 9800). This system provides pulsed digital cine (up to 150 mA) at 30 pulses per second with a 10-ms pulse width and true 1,000 ϫ 1,000 imaging resolution, allowing digital recording at 30 frames per s. The digital signal from the fluoroscope was recorded on a S-VHS (NTSC standard) video recorder (JVC Super VHS ET, model HR-S2901U) together with the sound recorded by a directional microphone (Sennheiser ME88) aimed at the bird from a distance of 1 m, as described elsewhere (19). All experiments were in compliance with the guidelines of the National Institutes of Health and were reviewed and approved by the Institutional Animal Care and Use Committee of Indiana University.…”

Vocal production mechanisms in a non-human primate: morphological data and a model

“…To address questions of motor patterns underlying vocal behaviour, the ideal approach is to observe the movement of the articulators in the animal's vocal tract during vocalisation, using cine-radiographic or related techniques (e.g. Fitch, 2000;Riede et al, 2004). For a number of reasons this approach was unsuitable here.…”

Vocal tract articulation revisited: the case of the monk parakeet

“…It has been shown, however, that the sound generated at the source can exhibit harmonic overtones (Beckers et al, 2003) and that cyclical movements of the hyoid skeleton or expansion of the cervical esophagus filter these out of the signal by tuning the oropharyngeal-esophageal cavity (OEC) to the fundamental frequency of the song (Riede et al, 2004;Riede et al, 2006;Riede and Suthers, 2009). Additionally, in zebra finches (Taeniopygia guttata), which produce a wide range of broad-band note types, expansion of the OEC has also been found to affect frequency patterns by shifting energy to relatively lower frequencies while amplitude generally increases (Ohms et al, 2010b).…”