Up to eight physiological parameters were measured on members of four species of fruit bats with a size range of 0.188-0.650 kg as they flew in a wind tunnel. Regression lines were calculated for the relationships between body masses of bats and their power inputs (P1), heart and respiratory rates. These were compared to similar relationships for flying birds.
Respiratory evaporation dissipated only 10% of the heat produced. At ambient temperatures (Ta) above 15°C, heat loss was facilitated by vasodilation of feet and wing membranes, but this mechanism became less effective at high Ta when thermal differential between wings and air was reduced. Bats are apparently unable to increase greatly their respiratory evaporation, and overheated at Ta of 25–30°C. At low Ta) the flight ability of two bats was reduced, suggesting that reduced coordination or even freezing of wings might be a general problem for bats flying at Ta close to 0°C.
The endurance of three bats was so much greater near the middle of their speed ranges that the maximum flight distances ought to be achieved at these velocities, even though the cost of transport would be lower at higher speeds. Endurance at an airspeed was proportional to the relative power input (Pi/Pi,min) raised to the power of −7.45; flying at a speed that raised Pi/Pi,min by 10% reduced endurance by half.