Respiratory evaporation in panting fowl: Partition between the respiratory and buccopharyngeal pumps

Ventilation (V) and respiratory water loss\(\left( {\dot M_{R,H_2 O} } \right)\) were measured in domestic fowlGallus gallus subjected to raised environmental temperatures (33±2°C) and breathing air, 8% O2 in N2, 3% CO2 in air or 5% CO2 in air. Birds breathing air underwent an 18.6-fold increase in respiratory frequency and a 5-fold reduction in tidal volume and panting was accompanied by vigorous gular flutter. Hypoxic and hypercapnic birds breathed more slowly and deeply and gular flutter was strongly inhibited. The\({{\dot M_{R,H_2 O} } \mathord{\left/ {\vphantom {{\dot M_{R,H_2 O} } {\dot V}}} \right. \kern-\nulldelimiterspace} {\dot V}}\) ratio was similar to that predicted on the basis of the measured ventilation assuming saturation of expired gas at measured gular mucosal temperature in hypoxic and hypercapnic birds but 54% greater than the predicted value in birds panting in air. It is concluded that the excess water loss during normal panting results from tidal airflow generated independently by the buccopharyngeal pump and that buccopharyngeal ventilation is equivalent to 54% of the respiratory ventilation.