Tidal volume (VT), respiration frequency (f) and respiratory evaporation (.ovrhdot.mre) were measured in the passeriform fish crow, C. ossifragus (mass 0.28 kg), during steady state, horizontal, wind-tunnel flight, at air speeds of 7.4-11.0 m .cntdot. s-1 and air temperatures (TA) of 12-28.degree. C. Ventilation (.ovrhdot.VI) of the respiratory system was calculated as f .cntdot. VT. All parameters were independent of speed. Respiration frequency was independent of TA. VT and .ovrhdot.VI were independent of TA below 23.degree. C, but above 23.degree. C increased linearly, as did .ovrhdot.mre. O2 extraction (E), the fraction of available O2 removed from respiratory system air, was calculated using O2 consumption data (.ovrhdot.VO2) reported previously and .ovrhdot.VI. E was independent of TA below 23.degree. C, where mean E, similar to that in crows resting at 20.degree. C, was substantially higher than in resting mammals of the same mass. E decreased at higher TA, reflecting hyperventilation accompanying elevated .ovrhdot.mre. The .ovrhdot.mre accounted for the loss of only 17% of total metabolic heat production (.ovrhdot.Hp), as calculated from .ovrhdot.VO2, with a partial efficiency of 25%. Most heat loss apparently must follow cutaneous evaporative, or non-evaporative routes.
