Biodiversity and dynamics of direction finding accuracy in bat biosonar

Abstract

In the biosonar systems of bats, emitted acoustic energy and receiver sensitivity are distributed over direction and frequency through beampattern functions that have diverse and often complicated geometries. This complexity could be used by the animals to determine the direction of incoming sounds based on spectral signatures. The present study in its first part has investigated how well bat biosonar beampatterns are suited for direction finding using a measure of the smallest estimator variance that is possible for a given direction (Cram{'e}r-Rao lower bound, CRLB). CRLB values were estimated for numerical beampattern estimates derived from 330 individual shape samples, 157 noseleaves (used for emission) and 173 outer ears (pinnae). At an assumed unit[60]{dB} signal-to-noise ratio, the average value of the CRLB was 3.9textdegree, which is similar to previous behavioral findings. Distribution for the CRLBs in individual beampatterns were found to have a positive skew indicating the existence of regions where a given beampattern does not support a high accuracy. The highest supported accuracies were for direction finding in elevation (with the exception of phyllostomid emission patterns). Beampatterns in the dataset were also characterized based upon the differences in the type of acoustic signal they are associated with, the functionality of the baffle shape producing them and their phylogeny. In the second part of the study, functionality of various local shape features was investigated under static and dynamic conditions. Each local shape feature was found to have an impact on the estimation performance of the baffle shape. Interaction of the local shape features among themselves as well as their dynamic motion produced a plethora of results, not achievable through either single features or through their static states only.