The Physiology and Energetics of Bat Flight

1. The energetics and physiological responses to flight of the echolocating bat Phyllostomus hastatus were studied to determine the energy requirements and physiological adaptations for mammalian flight. 2. The metabolic cost of bat flight is approximately comparable to that of bird flight and requires a metabolic rate appreciably greater than has been reported for terrestrial mammals during exercise. During flight P. hastatus consumed between 24.7 and 29.1 ml O2 (g h)-1, which is about four times its metabolic rate immediately prior to flight and more than 30 times its oxygen consumption while resting with a TR of 36.5 °C in a small chamber. 3. The onset of flight is accompanied by an abrupt increase in both the heart rate, from about 8.7 to 13 beats/sec, and the respiratory rate, from 3 to about 9.6/sec. Rectal temperature is elevated during flight and maintained at about 41.8 °C. The respiratory quotient, which averages 0.83 in a quietly resting bat, rises to a little over 1.0 during the first few minutes of flight. 4. The minimum estimated tidal volume during flight is about 1.4 ml. One respiratory cycle occurs with each wingbeat, corresponding to an estimated minute volume of 840 ml, which is comparable to that reported for the flying budgerigar. The amount of oxygen extracted by P. hastatus from a given volume of tidal air is also comparable to the efficiency of ventilation reported for this bird. 5. High hematocrit values of about 60%, and a high oxygen capacity of 27.5 vol % of P. hastatus blood, must represent important adaptations for enabling the flying bat to maintain such a high metabolic rate.