Circulation, respiratory volumes and temperature regulation of the pigeon in dry and humid heat

Abstract

1. 1. In an 8 km/hr breeze pigeons survived T a s † of 54·5°C in dry air and 42·5°C at 96% r.h. 2. 2. Blood pressure remained relatively constant in the heat. 3. 3. Relative humidity had no effect on the T b or T a at which the f first began to increase, but thereafter as the f slowly increased r.h. had a marked effect on evaporative cooling. 4. 4. Maximal f's of 650/min with V T's of 3–4 ml produced a V E max of 2·4 1/min at a T b of 46°C. This V E max was 23–25 times that during rest. 5. 5. The body plethysmograph, used to monitor respiration, blocked cutaneous evaporation of water which significantly hampered the pigeons' ability to thermoregulate when compared to free-standing controls.