THE COST OF HOVERING AND FORWARD FLIGHT IN A NECTAR-FEEDING BAT, GLOSSOPHAGA-SORICINA, ESTIMATED FROM AERODYNAMIC THEORY

Energy expenditure during flight in animals can best be understood and quantified when both theoretical and empirical approaches are used co ncurrently. This paper examines one of four methods that we have used to estimate the cost of flight in a neotropical nectar-feeding bat Glo ssophaga soricina (Phyllostomidae), namely the use of kinematic and mo rphological data and aerodynamic theory to estimate the mechanical pow er requirements (power output) for hovering and horizontal forward fli ght. A hot-wire anemometer was used to measure induced velocity (the v elocity of air accelerated by the wings) during hovering in order to e stimate induced power. Our estimate of aerodynamic power (the sum of i nduced, profile and parasite powers) required for a 0.0105 kg G. soric ina to hover is 0.15 W and our estimate of the inertial power (the pow er required to oscillate the wings) is 0.19 W. Thus, the total mechani cal power for hovering is 0.34 W or 32.4 W kg-1. The mechanical power required for horizontal forward flight, near the minimum power flight speed (4.2 ms-1) for a 0.0117 kg bat is 0.14 W (12.3 W kg-1), of which 0.10 W is aerodynamic power and 0.042 W is inertial power. Comparison with our results on metabolic power requirements estimated from necta r intake gives a mechanical efficiency of 0. 15 for hovering flight an d of 0.11 for forward flight near the minimum power speed.