The Ostrich (S&u&o cumelus), the largest living bird, is an inhabitant of semi-arid and desert areas of Africa and, until exterminated, the Near East and the Arabian Peninsula. When exposed to the heat stress of a hot desert, it must use water for evaporation in order to avoid overheating. While its size prevents it from taking advantage of microclimates to the extent that small desert birds and mammals can, its large size is an advantage in its water economy, as has been discussed previously (Schmidt-Nielsen 1964). Birds have no sweat glands, and under heat stress they rely upon increased evaporation from the respiratory system as a major avenue for heat dissipation. We were interested in the role of the respiratory system in evaporation, and particularly in the sites of evaporation. Furthermore, while in mammals an increased ventilation causes alkalosis, in birds the presence of large air sacs connected to the respiratory system may have radically different effects on the gas exchange in the lung. Finally, the fact that the ventilation of the respiratory system can be modified by heat stress without change in the rate of oxygen consumption may provide an avenue for investigation of the poorly understood air-sac system of birds. The Ostrich, although a non-flying bird, has a well developed air-sac system, and its large size and slow breathing rate provide an o,pportunity to undertake experimental procedures which in smaller birds result in great technical difficulties or seem impossible. 1 Deceased 7 April 1967. MATERIALS AND METHODS Birds Twenty semi-domesticated adult Ostriches weighing 63-104 kg (12 males and 8 females) were purchased from commercial sources near Oudtshoom in South Africa and transported by rail to Onderstepoort Veterinary Research Institute near Pretoria. They were permitted to graze freely in a 30-acre enclosure and were fed daily with fresh alfalfa and dry corn (maize). Water was provided at all times, except when it was removed as part of the experimental procedure. Handling facilities permitted the separation of smaller or larger numbers of birds as well as the isolation and/or capture of a given individual. Ostriches are very powerful birds and difficult as well as dangerous to handle. For all experimental procedures that required a close approach, the desired bird was driven into a chute, provided with a hood, and transferred to a horizontal V-shaped restraining device, the design of which was based on the restraining procedures used for the commercial plucking of Ostrich feathers from living birds. Once the bird was completely restrained, the hood could be removed. Most experimental procedures did not require the use of tranquilizers or general anesthesia. However, where catheterization of blood vessels or other cutting procedures were involved, local anesthesia was achieved with xylocaine. During measurements of surface temperatures in the trachea and the air sacs, the birds were tranquilized with M 99 (etorphine hydrochloride, Reckitt & Sons, Ltd.). Weighing. Body weights of individ...
