An experimental link between fast noseleaf deformations and biosonar pulse dynamics in hipposiderid bats

Abstract

Old-World leaf-nosed bats (Hipposideridae) are echolocating bats with peculiar emission-side dynamics where beamforming baffles ("noseleaves") that surround the points of ultrasound emission (nostrils) change shape while diffracting the outgoing biosonar pulses. While prior work with numerical and robotic models has suggested that these noseleaf deformations could have an impact on the output characteristics of the bat's biosonar system, testing the hypothesis that this is the case in bats remains a critical step to be taken. The work presented here has tested the hypothesis that the noseleaf dynamics in a species of hipposiderid bat (Pratt's roundleaf bat, H. pratti) leads to time-variant acoustical properties on the output side of the bats' biosonar emission system. The time-variant effects of the noseleaf motion could be detected even in the presence of other sources of variability by comparing the distribution of pulse energy over the angle at different points in time. Furthermore, a convolutional neural network was able to classify the noseleaf motion state based on microphone array recordings with 85.3% accuracy. These results hence demonstrate that these nose-emitting bats have access to a substrate for behavioral flexibility on the emission-side of their biosonar systems.