J. exp. Bio/. (1978), T*> 229-250 With iSfigurei Printed in Great Britain RESPIRATORY MECHANICS OF SOUND PRODUCTION IN CHICKENS AND GEESE BY J. H. BRACKENBURY Sub-Department of Veterinary Anatomy, Tennis Court Road, Cambridge, CBz iQS (Received 21 June 1977) SUMMARY 1. Air flow, air sac pressure and tracheal pressure were measured in chickens and geese during a variety of different vocal and non-vocal activities. 1 2. Air flow and air sac pressure may rise to 500 ml s" and 60 cmH2O (6 x io3 N/m8) respectively during a crow in the chicken. During a sequence -1 of honks in the goose the corresponding values are 650 ml s and 25 cmH2O (2-5 x 1 o3 N/m2) respectively. 3. The volume of air delivered through the respiratory system during a single crow is more than 400 ml, almost equivalent to the total volume of the lung air sac system. 4. The efficiency of the chicken syrinx as a sound producing instrument, estimated by comparing the sound energy radiated with the energy con- sumed in the expulsion of air during a crow, appears to be less than 2 %. 5. Cutting the paired sternotrachealis muscles had no effect on vocalization. 6. The measured rates of clucking, cheeping and honking in adult chickens, young chicks and adult geese respectively are comparable to the characteristic rates of panting in these animals. This points to a similarity in the nature of the respiratory movements involved in each case. 7. Simultaneous measurement of tracheal flow and pressure indicate that the glottis is capable of controlling air flow over a wide range of values in the presence of high pressures. During defaecation the valve is closed whilst during coughing it is wide open. INTRODUCTION Gaunt, Stein & Gaunt (1973) and Gaunt, Gaunt & Hector (1976) have compared the mechanical events associated with sound production in a songbird, the starling Sturnus vulgaris, and the chicken Gallus domesticus. They found marked differences between the two types in their ability to regulate respiratory air flow during vocal- ization. In both cases there were very large increases in air sac pressure but the starling was able to restrict both the air flow rate and the total amount of air used. This was presumably made possible by means of a valvular constriction of the syrinx brought about by the action of the intrinsic syringeal muscles. Gaunt et al. were unable to record air flow directly in the chicken but adduced from recordings of tracheal pressure that the syringeal valve was much less effective in this species. This is probably associated with the lack of intrinsic muscles. On the other hand there was evidence Present address: Department of Biology, University of Salford, Salford, Manchester Ms 4WT. 230 J. H. BRACKENBURY of a very substantial increase in flow resistance during a form of vocalization which they called ' wailing'. This was attributed to the action of the extrinsic muscles of the syrinx, notably the sternotrachealis muscles. The supposed mechanism of these muscles had first been described by Miskimen (1951). By their action, the drum of the syrinx was said to be drawn caudally, which led to an inward bowing of the tympani- form membranes and a narrowing of the syringed lumen. Gaunt et al. also considered whether the movements of the body involved in clucking in chickens represented expiratory pulsations or true in/out breaths. Calder (1970) had shown that trilling in the canary Serinus canaria was accompanied by rapid vibrations of the sternum which he described as 'mini-breaths'. Gaunt et al. doubted this interpretation, believing the movements here, as well as in the chicken, to be expiratory pulsations. The problem, which remains unsolved, has an important bearing on the ability of certain birds to breathe during long periods of continuous high frequency singing. Brackenbury (1977) has discussed the matter in relation to the production of continuous trains of pulsed sounds in the grasshopper warbler Locustella naevia. The main purpose of the present paper is to investigate the relationship between changes in pressure and flow in the lung air sac system of chickens and geese during vocalization, by direct recording. This will include a quantitative assessment of the efficiency of the syrinx as a sound producing organ. In addition, the nature of the respiratory drive involved in pulsed sound production will be studied by comparing mechanical events during clucking and panting. Finally, direct evidence will be presented from a variety of vocal and non-vocal activities, showing that the glottis, as well as the syrinx, is capable of acting as a variable and efficient valve in the respiratory system. METHODS All recordings were made from standing birds with chronically implanted cannulae and air flow meters. Before surgery birds were anaesthetized with a mixture of equal proportions of 30 % ethyl carbamate (Urethane) and sodium pentobarbitone (Nem- butal) introduced steadily into the wing vein. Chickens (B.W. 2'5-3-3 kg) required 3-4 ml, geese approximately twice this amount. The interdavicular air sac was can- nulated at the base of the neck on the left side in order to avoid the crop. The tracheal flow meter (Fig. 1) is designed on the Pitot principle and is similar to the instrument used by the author for measuring intrapulmonary air flow (Brackenbury, 19726). It can be calibrated in situ in the standing animal (Fig. 2) or post mortem after removal of the trachea. It is introduced into the trachea through two small holes cut in the cartilage and involves minimal obstruction of the flow of air and mucus. Apart from immediate post-operative effects, its presence caused no apparent distress to the animals. Tracheal pressure could be monitored by leading off one arm of the instrument simultaneously to a second manometer. Pressures from both the flow meter and the cannulae were measured using Grass PT5 manometers feeding into a Grass Model 7 polygraph. The frequency response of the pressure recording/polygraph system was mainly limited by the pen oscillograph which was flat from d.c. to 35 Hz and down 3 dB at 75 Hz. A Briiel and Kjaer 4161 microphone connected to a Nagra IV SJS recorder was used for sound recording. Sound signals were led into a Grass 7P3 integratoi Sound production in chickens and geese 231 1 ' i * L iiit ii Fig. 1. Tracheal flow meter. The device is constructed on the Pitot principle. It consists of two tubes fixed to a half cylinder of plastic which, together with a small sleeve of tubing (i), holds the device in place in the trachea (J1). Air flow (V) produces a pressure difference between the two holes Pj and P, and this is measured by a differential manometer. which produced at the output to the pen recorder a voltage proportional to the average sound pressure level. The frequency response of the sound recording system was flat from 30 Hz to 15 KHz ± 1 dB at a tape speed of "j\ in/s. RESULTS Chicken Crowing The sound recording in Fig. 3 shows the main features of the normal crow in an unoperated animal. Three introductory notes (marked by arrows) occurring at a rate of 4-5 Hz, lead into a prolonged phase in which the average sound pressure level falls from a maximum of approximately 100 dB measured in front of the animal, to zero. Measured from behind the peak sound level is approximately 95 dB. All sound pressure values are given with reference to 0-0002 dyne/cm2 at a distance of 1 m. The changes in air sac pressure during a crow are shown in Fig. 4. Similar re- cordings have been presented by Brackenbury (1972 a) and Gaunt et al. (1976). The first half of Fig. 4 shows a sequence of normal breaths leading up to the crow. In the second half the chart speed was increased to show the details of the crow. The main features, including the introductory notes and the prolonged phase, are reflected in the pressure changes. The maximum pressure is slightly less than 60 cmHaO (6x io3 N/m2). The crow takes place during an exceptionally strenuous expiration; Ifis the figure shows, it is not preceded but is followed by a deep inspiration. At the 232 J. H. BRACKENBURY 166 . [Trachea! flowm i J^ Fig. a. Tracheal flow meter. Calibration in situ. This makes use of the technique of artificially ventilating the lung air sac system by means of a measured stream of air led into the interdavicular air sac and out of the mouth. Upper trace: flow rate was measured by a Fleisch pneumotachograph. Lower traces: air sac pressure and flow meter differential. Respiratory movements are indicated before and after the period of calibration, but are inhibited as soon as the air stream is switched on. Time in seconds. I•e 95 Fig. 3. Chicken. Crowing. Sound recording from normal unoperated animal. The arrows indicate the three typical introductory notes. mrt mi Ti 3- I s Fig. 4. Chicken. Crowing. Interclavicular air sac pressure. The chart speed was increased from the first half of the recording, showing a sequence of normal breaths, to the second half showing the crow. 234 J. H. BRACKENBURY 60 -i 40- O- gj _ Sound pressure fevell ,§ t — =z § = ^p e 85 HI 0Q •a Fig. 5. Chicken. Crowing. Air sac pressure, tracheal pressure and average sound pressure level. Time in seconds. end of the crow the pressure falls dramatically from approximately +4ocmHliO 3 1 a (4 x io N/m ) to approximately -7 cmH20 (7 x io* N/m ). The latter value may be compared to the minimum inspiratory pressure during a normal breath, which is -(1-1-5) cmHjO (ro-i-5 x io2 N/ma).