Ventilation and respiratory evaporation in the flying crow, Corvus ossifragus

Tidal volume (VT), respiration frequency (f) and respiratory evaporation (mre) were measured in the passeriform fish crow, Corvus ossifragus (mass 0.28 kg), during steady state, horizontal, wind-tunnel flight, at air speeds of 7.4-11.0 m-sec-1 and air temperatures (TA) of 12-28 degrees C. Ventilation (V1) of the respiratory system was calculated as f-VT. All parameters were independent of speed. Respiration frequency was independent of TA. VT and V1 were independent of TA below 23 degrees C, but above 23 degrees C increased linearly, as did mre. Oxygen extraction (E), the fraction of available oxygen removed from respiratory system air, was calculated using oxygen consumption data (VO2) reported previously, and VI. E was independent of TA below 23 degrees C, where mean E, similar to that in crows resting at 20 degrees C, was substantially higher than in resting mammals of the same mass. E decreased at higher TA, reflecting hyperventilation accompanying elevated mre. mre accounted for the loss of only 17% of total metabolic heat production (Hp), as calculated from VO2, with a partial efficiency of 25%. Thus most heat loss must follow cutaneous evaporative, or nonevaporative routes.