6.7  Wednesday, Jan. 4  Energetics of Bat Flight VON BUSSE, J.R.S.*; SWARTZ, S.M.; BREUER, K.S.; HEDENSTRÖM, A.; WINTER, Y.; VOIGT, C.C.; Brown University, Providence, RI; Brown University, Providence, RI; Brown University, Providence, RI; Lund University, Sweden; Humoldt University, Berlin, Germany; Leibnitz Institute, Berlin, Germany rhea_vonbusse@brown.edu

The goal of this study is to directly test the U-shaped flight velocity – power curve predicted by aerodynamic theory for the first time in bats. We carried out this test by measuring energy expenditure during flight in a wind tunnel over a broad range of flight speeds. We employed two experimental methods: we used open flow respirometry to measure oxygen consumption of Leptonycteris yerbabuenae flying from hovering to seven m/s, and used the sodium bicarbonate method, spectrometry of a labeled carbon isotope incorporated into expired carbon dioxide, for Carollia perspicillata flying from one to seven m/s. Both study species are nectar feeders that metabolize sugar almost exclusively, which allows for accurate conversion of oxygen consumption into metabolic energy.
By comparing aerodynamic power output and metabolic power input, it is possible to estimate mechanical efficiency of flight. Because the power requirement for level forward flight equals speed times total drag, mechanical power output can be estimated from drag measurements. We made these assessments from aerodynamic measurements using stereo digital particle image velocimetry (SDPIV).
We found that metabolic rate measured by open flow respirometry did not change significantly over the speed range. The sodium bicarbonate experiments demonstrate that most animals show strong velocity dependence in metabolic expenditure for flight. However, some individuals did not conform to this pattern, and employ different energetic strategies with changing flight speeds. Mechanical efficiency measured for Leptonycteris yerbabuenae follows a U-shaped curve, with values between 18 and 23%.