Biosonar beampattern measurements in flying old world leaf-nosed bats

Abstract

Emission beampatterns, i.e., emitted ultrasound amplitude as a function of direction and frequency, could be an important characteristic of a bat's biosonar since they determine which part of an environment is illuminated with a given frequency and at a given time. Numerical results have predicted intricate geometrical features such as multiple peaks and notches in bat biosonar beampatterns. Furthermore, it has been shown that bats with nasal emission change the shapes of their emission baffles, “noseleaves,” during pulse emission. The work presented here is aimed at understanding if and how these two aspects (beam geometry and emission dynamics) are integrated into the bats' biosonar behaviors on the wing. The experiments are conducted with Old World leaf-nosed bats (Hipposideros pratti and Hipposideros armiger) that have a pronounced noseleaf dynamics. The animals fly in a tunnel that is instrumented with synchronized arrays of high-speed video cameras and microphones. The setup allows for precise tracking of the bats with high spatial resolution as well as beampattern estimates as a function of time. A first pilot dataset has indicated the presence of local shape features in the beampattern that can also vary with time. However, further testing is needed to corroborate these findings.Emission beampatterns, i.e., emitted ultrasound amplitude as a function of direction and frequency, could be an important characteristic of a bat's biosonar since they determine which part of an environment is illuminated with a given frequency and at a given time. Numerical results have predicted intricate geometrical features such as multiple peaks and notches in bat biosonar beampatterns. Furthermore, it has been shown that bats with nasal emission change the shapes of their emission baffles, “noseleaves,” during pulse emission. The work presented here is aimed at understanding if and how these two aspects (beam geometry and emission dynamics) are integrated into the bats' biosonar behaviors on the wing. The experiments are conducted with Old World leaf-nosed bats (Hipposideros pratti and Hipposideros armiger) that have a pronounced noseleaf dynamics. The animals fly in a tunnel that is instrumented with synchronized arrays of high-speed video cameras and microphones. The setup allows for precise track...