Meeting Abstract

39.3  Jan. 6  The effect of artificial loads on the straight flight performance of fruit bats IRIARTE-DIAZ, J.; Brown University jose_iriarte@brown.edu

Most bats experience significant fluctuations in their body mass. These fluctuations can be both daily, mostly due to feeding, or seasonal due to fat storage and/or reproduction. Based on predictions derived from classic aerodynamic theory, increments in body mass, such as those in observed in natural populations of bats, should severely affect their flight performance. But because bat flight is spatially and temporally complex, and bat wings continuously change shape during a wingbeat, the utility of such theoretical models is limited. For example, some bats species are able to increase their body mass up to 40% and remain capable of maneuvering in complex three-dimensional environments. How increased lift is produced when weight is increased is well understood. Thus, the purpose of this study is to evaluate the effect of added mass on the kinematics of forward, steady flight in a fruit bat. Three lesser short-nosed fruit bats (Cynopterus brachyotis) were trained to fly in a flight corridor with and without carrying a load of about 20% of their original body mass. Ultra-light reflective markers were placed on the body and wings and flights were recorded with three synchronized, high-speed digital video cameras in low light conditions. Data from the three cameras were combined to reconstruct the 3D motion of each marker. From these recordings, flight speed and body and wing kinematic parameters were obtained for each treatment. Experimental bats showed a 27% increase in speed with a 20% increase in body mass. Wingbeat frequency and amplitude, however, did not change with load, suggesting that more subtle changes in wing configuration (e.g., angle of attack, camber) must be used to generate enough lift to compensate for the increased weight.