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Temperature Regulation and Respiration in the Ostrich

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Temperature Regulation and Respiration in the Ostrich TEMPERATURE REGULATION AND RESPIRATION IN THE OSTRICH KNUT SCHMIDT-NIELSEN, JOHN KANWISHER, lIepartment of Zoology Woods Hole Oceanographic Institute Duke University Woods Hole, Massachusetts 02453 Durham, North Carolina 27706 ROBERT C. LASIEWSKI, JEROME E. COHNl, Department of Zoology University of Kentucky Medical Center Universitv of California Lexinnton.y , Kentucky 40506 Los Angeles, California 90024 AND WILLIAM L. BRETZ Department of Zoology Duke University Durham, North Carolina 27706 The Ostrich (S&u&o cumelus), the largest MATERIALS AND METHODS living bird, is an inhabitant of semi-arid and Birds desert areas of Africa and, until exterminated, the Near East and the Arabian Peninsula. Twenty semi-domesticated adult Ostriches weighing 63-104 kg (12 males and 8 females) were pur- When exposed to the heat stress of a hot chased from commercial sources near Oudtshoom in desert, it must use water for evaporation in South Africa and transported by rail to Onderstepoort order to avoid overheating. While its size Veterinary Research Institute near Pretoria. They prevents it from taking advantage of micro- were permitted to graze freely in a 30-acre enclosure climates to the extent that small desert birds and were fed daily with fresh alfalfa and dry corn (maize). Water was provided at all times, except and mammals can, its large size is an ad- when it was removed as part of the experimental vantage in its water economy, as has been procedure. Handling facilities permitted the separa- discussed previously ( Schmidt-Nielsen 1964). tion of smaller or larger numbers of birds as well as the Birds have no sweat glands, and under heat isolation and/or capture of a given individual. Ostriches are very powerful birds and difficult as stress they rely upon increased evaporation well as dangerous to handle. For all experimental from the respiratory system as a major ave- procedures that required a close approach, the de- nue for heat dissipation. We were interested sired bird was driven into a chute, provided with a in the role of the respiratory system in evapora- hood, and transferred to a horizontal V-shaped re- tion, and particularly in the sites of evapora- straining device, the design of which was based on the restraining procedures used for the commercial tion. Furthermore, while in mammals an plucking of Ostrich feathers from living birds. Once increased ventilation causes alkalosis, in birds the bird was completely restrained, the hood could the presence of large air sacs connected to the be removed. respiratory system may have radically different Most experimental procedures did not require the use of tranquilizers or general anesthesia. However, effects on the gas exchange in the lung. where catheterization of blood vessels or other cutting Finally, the fact that the ventilation of the procedures were involved, local anesthesia was respiratory system can be modified by heat achieved with xylocaine. During measurements of surface temperatures in the trachea and the air sacs, stress without change in the rate of oxygen the birds were tranquilized with M 99 (etorphine consumption may provide an avenue for in- hydrochloride, Reckitt & Sons, Ltd.). vestigation of the poorly understood air-sac Weighing. Body weights of individual birds were system of birds. determined with the animal in a portable restraining device placed on a platform scale (precision about The Ostrich, although a non-flying bird, has 0.1 kg). Accurate changes in body weight used for a well developed air-sac system, and its large the determination of evaporative water loss were de- size and slow breathing rate provide an o,p- termined by suspending the bird in its restraining portunity to undertake experimental proce- device from the arm of a beam balance (designed according to Krogh and Trolle 1936, and modified dures which in smaller birds result in great with magnetic damping). This weighing did not pro- technical difficulties or seem impossible. vide the absolute weight of the animal, but gave weight changes with a precision better than 5 g. 1Deceased 7 April 1967. Since the evaporation might reach 10 g/min, the 13411 The Condor, 71:341-352, 1969 342 SCHMIDT-NIELSEN, KANWISHER, LASIEWSKI, COHN, AND BRETZ accuracy of the determinations of evaporation by of arterial and venous blood samples was also de- weighing was more than adequate. Correction for termined directly with the oxygen electrode. metabolic loss of carbon is unnecessary at such high The carbon dioxide tension of blood was determined rates of water loss and was not employed. by the Astrup method using Radiometer tonometer, Temperature-controlled room. All experiments which microelectrode, and PHM-4 pH meter. For unex- involved exposure to high temperatures were car- plained reasons the pH values of the Ostrich blood ried out in a room about 2.3 x 3.5 x 2.3 m high. did not consistently remain stable, although the same The temperature in this room was controlled to method has previously been used by us for blood of about f 1°C. The humidity in the room was not other birds without encountering this difficulty. How- under control, but high humidities were avoided by ever, by bracketing samples between suitable gas introducing outside air at a high rate. mixtures it was possible to obtain reliable determina- Temperature measwements. Cloaca1 temperatures tions of the CO, tension in the blood samples. were usually obtained by thermistor measurements Pressures in the airways. Air pressures were de- (Yellow Springs Instrument Co.) and occasionally termined by attaching a sensitive pressure transducer by mercury thermometers. During measurements of (Computer Instruments Corp., Type 6000, range tracheal temperatures the cloaca1 temperature was -0.3 to 0.3 psi) to a needle inserted into the ap- monitored with thermocouples made from 30-gauge propriate place, and the output was recorded on the copper-constantan wire. same Esterline-Angus Recorder used for thermocouples Temperatures in the respiratory system (surface as ( see above 1. Differential _nressures within the airwavs well as air) and skin temperatures were measured were recorded with the same transducer. with X-gauge copper-constantan thermocouples and Cutaneous water loss. Cutaneous water loss was recorded on an Esterline Angus Speed Servo AZAS determined by the weight increase of silica gel Recorder. The accuracy of these measurements was (Randall and McClure 1949). About 30 g silica gel about 0.5”C. Since the cloaca1 temperature was an was placed in a cylindrical aluminum container and important reference point in all these measurements, kept in place by a press-fitted piece of wire mesh. it was monitored simultaneously with the same re- The opening of the container covered a skin area corder. of 31.2 cm*. Cloaca1 temperature during exercise was measured Volumes of respiratory system. Tracheal volume with a temperature telemetering transmitter (range in was determined by filling excised tracheas with water excess of 2 km, accuracy about f. 0.2”C). and measuring the volume in a graduated cylinder. Respiration. Respiratory rates (frequency) were This method, because of expansion of the trachea determined either by counting and using a stopwatch, under pressure, will yield values somewhat too high, or by recording temperature oscillations at the nares but because of the exceptional rigidity of the Ostrich or in the trachea. trachea the error is not likely to be great. No at- Respiratory volumes were obtained by fitting a tempt was made to correct for this error. mask on the animal and collecting the expired air. Air sac volumes were determined either by weighing The mask was constructed from a plastic bottle of gelatin casts after filling the entire respiratory system suitable shape, fitted to the head, and provided with with gelatin and dissecting out the casts, or by a dilu- a sleeve of soft rubber dam which was kept closely tion technique which employed the quick injection assembled around the neck with a series of rubber into an air sac of 100 ml of oxygen (containing 2.2 bands. Pressure changes in the mask, and therefore per cent CO,). Continuous recording of the change leakage, were minimized by the use of a high flow, in oxygen concentration permitted an approximate six-element MacGregor valve. Expired air was col- determination of dilution volumes as well as the wash- lected in large meteorological balloons and the volume out time of the individual air sacs in normal respiration immediately measured with a dry gas meter ( ? 1 per at rest. During panting this approach could not be cent). When desired, air samples were withdrawn used because of the relatively slow response time from the respiratory system (air sacs and trachea) of the oxygen electrode (a few seconds). with 5-ml glass syringes provided with three-way metal valves and no. 16 needles of appropriate length. RESULTS For continuous recording of the oxygen tension in different air sacs, a no. 16 needle was inserted into BODY TEMPERATURE AND the appropriate air sac and the air drawn con- TOTAL EVAPORATION tinuously over a quick-responding oxygen electrode The Ostriches could maintain their body tem- by means of an aquarium pump. perature at a stable level during prolonged ex- Gas analysis. Air samples taken with glass syringes were analyzed on a Scholander 0.5 ml Gas Analyzer posure to a range of ambient temperatures of ( Scholander 1947 ). Continuous monitoring of oxygen 15 - 50°C (fig. 1). At the highest tempera- tension was done with an oxygen electrode according tures they became slightly hyperthermic, but to Kanwisher ( 1959), using a 12-p teflon membrane in order to obtain rapid response. The system of the many could still maintain their body tempera- oxygen electrode with the sampling needle attached ture at a stable level below 40°C for periods responded to changes in gas composition within 0.5 as long as 8 hr at 50°C ambient.
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