Echolocation and flight strategy of Japanese house bats during natural foraging, revealed by a microphone array system

Using only a microphone array system, echolocation pulses and three-dimensional flight paths in the frequency-modulated bat, Pipistrellus abramus, during natural foraging, were simultaneously examined. During the search phase, the inter-pulse interval, pulse duration, and moving distance of the bat between successive emissions were relatively constant at around 89.5 ± 18.7 ms, 6.90 ± 1.31 ms, and 0.50 ± 0.20 m, respectively. The bats started to decrease these acoustical parameters within 2-3 m of the prey capture point. For every emission along a flight path, the distance between a bat and its prey capture point was calculated as both direct distance to capture (DDC), which corresponded to the target distance, and flight distance to capture (FDC) along the flight path. The DDC matched the FDC after the start of the approach phase, indicating that foraging bats followed a straight-ahead path to the target. In addition, the duration of the quasi-constant frequency component of emitted pulses was slightly extended just before the convergence of the DDC with the FDC. These findings suggest that the bats confirm the presence of target prey by extending the duration of the pulse and then select a straight-ahead approach by forecasting the movement of the prey.