Respiratory water loss in free-flying pigeons

Abstract

SUMMARY We assessed respiratory and cutaneous water loss in trained tippler pigeons (Columba livia) both at rest and in free flight. In resting pigeons, exhaled air temperature Tex increased with ambient air temperature Ta (Tex=16.3+0.705Ta) between 15°C and 30°C, while tidal volume VT (VT=4.7±1.0 ml, mean ± s.d. at standard temperature and pressure dry) and breathing frequency fR (fR=0.46±0.06 breaths s–1) were independent of Ta. Respiratory water loss, RWL, was constant over the range of Ta (RWL=1.2±0.4 mg g–1 h–1) used. In flying pigeons, Tex increased with Ta (Tex=25.8+0.34Ta), while fR was independent of Ta (fR=5.6±1.4 breaths s–1) between 8.8°C and 27°C. Breathing frequency varied intermittently between 2 and 8 breaths s–1 during flight and was not always synchronized with wing-beat frequency. RWL was independent of air temperature (RWL=9.2±2.9 mg g–1 h–1), but decreased with increasing inspired air water vapor density (ρin) (RWL=12.5–0.362ρin), whereas cutaneous water loss, CWL, increased with air temperature (CWL=10.122+0.898Ta), but was independent of ρin. RWL was 25.7–32.2 %, while CWL was 67.8–74.3 % of the total evaporative water loss. The data indicate that pigeons have more efficient countercurrent heat exchange in their anterior respiratory passages when at rest than in flight, allowing them to recover more water at rest at lower air temperatures. When evaporative water loss increases in flight, especially at high Ta, the major component is cutaneous rather than respiratory, possibly brought about by reducing the skin water vapor diffusion resistance. Because of the tight restrictions imposed by gas exchange in flight, the amount of water potentially lost through respiration is limited.