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First published online October 21, 2004
Journal of Experimental Biology 207, 4025-4036 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01256

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Inflation of the esophagus and vocal tract filtering in ring doves

Tobias Riede^1,*, Gabriël J. L. Beckers^1,, William Blevins² and Roderick A. Suthers¹

¹ Medical Sciences, Indiana University, Bloomington, IN 47405, USA
² Department of Veterinary Clinical Sciences, Diagnostic Imaging Section, Purdue University, West Lafayette, IN 47907, USA

View larger version (19K): [in a new window]   Fig. 1. Changes in the amount of esophageal inflation during a sequence of two coos. The enlargement of the esophagus (top graph) is produced by airflow through the syrinx in the expiratory direction while the beak and nares are closed. Complete beak closure, as seen in the x-ray video, is indicated by arrow 1. The amount of inflation was estimated by measuring the area of the esophagus (shaded area on the drawing of the dove) in the two-dimensional x-ray image. Maximum inflation occurs at the end of the coo (arrows 2 and 3). The esophagus does not completely collapse between bouts of cooing. Coos are shown spectrographically (middle panel) and as an oscillogram (bottom panel). i, inspiratory note; e1, first note of the coo; p, pause between first and second note; e2, second note of the coo.

View larger version (79K): [in a new window]   Fig. 2. (A,B) Cineradiograph of a cooing ring dove during maximum inflation of the esophagus; (A) lateral view; (B) frontal view. The course of the trachea around the esophagus is indicated by arrowheads. The crop represents a separate cavity from the inflated upper esophagus. (C,D) Schematic drawing of the (C) lateral and (D) frontal view of a dove during full inflation of the esophagus. Cr, crop; Es, esophagus; Lx, larynx; Tn, tongue; Tr, trachea. Drawings by Sue Anne Zollinger.

View larger version (40K): [in a new window]   Fig. 3. Vocalizations and sounds recorded in different compartments of the vocal tract. (A) Emitted vocalization and tracheal sound from the same coo. (B) Emitted vocalization and esophageal sound from the same coo, uttered by a different dove. Oscillogram (top panels), spectrogram (middle panels) and power spectrum (bottom panels) of signals recorded in different compartments of the vocal tract. The DC offset in the e2 note of the tracheal and the esophageal signals is due to the pressure increase in the respective compartments. This offset can vary from coo to coo, although it appears similar in the examples shown. Coos in A and B come from different individuals.

View larger version (12K): [in a new window]   Fig. 4. Relative level of harmonics in the emitted vocalization and in the tracheal and esophageal sound. Each data point indicates the mean ± S.D. for individual birds. Horizontal lines indicate the mean sound level for the anatomical compartment, calculated from the mean individual values.

View larger version (20K): [in a new window]   Fig. 5. Relative level of harmonics (upper panel) in the middle of the e1 note (measured around point A) and at the end of the e2 note (measured around point B). The lower panel shows the spectrogram of a coo with the points of measurements indicated by vertical dotted lines.

View larger version (30K): [in a new window]   Fig. 6. Oscillograms and spectrograms of coo vocalizations (A) before esophageal tube was implanted, (B) after tube implant surgery and with closed tube and (C) after tube implant surgery and with open tube. The power spectra (bottom panels) are derived from a 100 ms segment during the second half of the e2 note, centered on the time indicated by the dotted line in the spectrogram.

View larger version (14K): [in a new window]   Fig. 7. Schematic drawing of the ring dove's suprasyringeal vocal tract during full inflation of the esophagus. Dimensions are in cm. Tracheal diameter varies somewhat along its length, and its cross-section is not perfectly circular.

View larger version (9K): [in a new window]   Fig. 8. Relationship between laryngeal opening and the first resonance (F1) of the trachea, calculated using equation 3 for a uniform tube closed at one end with a variable opening at the other end.

View larger version (35K): [in a new window]   Fig. 9. Time series, spectrogram and spectra of an inspiratory sound. The spectra were derived from 50 ms segments centered around the dotted lines at the beginning and end of the call. The spectra A and B show the fast Fourier transform (FFT)-based spectrum (lower curve) and the linear predictive coding-based envelope of power spectrum (see Owren and Bernacki, 1998) indicating formant frequencies. While the fundamental frequency is increasing from 165 Hz to 170 Hz, the first resonance (F1) increases from 500 Hz to 850 Hz.