Oxygen consumption was measured during flight in two flying foxes (Pteropus poliocephalus) at airspeeds of 4–8.6ms−1. There was good agreement with the measured power input of the only previously measured large bat, and with an allometric equation predicting power input for flying vertebrates. Measurements of respiratory exchange ratios, pulmonary water loss, respiratory frequencies, heart rates and body temperatures of both bats flying at intermediate airspeeds were compared with equivalent measurements on other bats or birds in flight. Despite a high non-evaporative thermal conductance in flight, the P. poliocephalus became severely hyperthermic at ambient temperatures (Ta) above 25°C. The failure to dissipate heat as successfully as flying birds at high Ta is apparently the result of an inability to increase pulmonary ventilation rates, and thus increase rates of evaporative heat loss.
The effect of airspeed on endurance was measured systematically on one bat. Endurance was not limited by energy reserves at all airspeeds, and flight times were significantly greater at the airspeed of minimum power input (Vmp). The endurance of both bats was so reduced at the higher airspeeds that they would not achieve maximum flight range in still air at the velocity where cost of locomotion is lowest. Contrary to a common assumption, flight range would be maximized at the Vmp.