Dynamic behavioral strategies during sonar signal emission in roundleaf bats.

For echolocating bats which emit biosonar pulses nasally, their nostrils are surrounded by fleshy appendages that diffract the outgoing ultrasonic waves. The posterior leaf, as a prominent part of the noseleaf, was mentioned in previous preliminary observations to move during flight in some species of bats, yet the detailed motion patterns and thus the possible functional role of the posterior leaf movement in biosonar systems remain unclear. In the current work, the motion of the posterior leaf of living pratt's roundleaf bats has been investigated quantitatively. Temporal characterizations of the noseleaf movement and the ultrasonic pulse emission were performed by virtue of synchronized laser vibrometry and sound recording. The results showed that the posterior leaf tilted forwards and restored to original position within tens of milliseconds. Noseleaf motions were temporally correlated with the emitted ultrasonic pulses. The surfaces of the posterior leaf were moving in the anterior direction in most of the pulse duration. The bats were able to switch the motions on or off. From the comparison with the previously reported noseleaf dynamics in horseshoe bat, we find similar ratio sizes and displacements of the noseleaves compared to the used wavelengths, implying that similar behavioral strategies are utilized by species of bats and it may be applied to different components of the signal emitting apparatus. It suggests that the dynamic sensing principles may widely play a role in the biosonar systems and the investigation on time-variant mechanisms is of capital importance to understand the biosonar sensing strategies used by echolocating bats.