Ear deformations in the biosonar system of horseshoe bats.

Abstract

Many bat species exhibit conspicuous ear movements as part of their biosonar behaviors. The resulting transformations of the pinnae can contain rigid rotations as well as nonrigid deformations. Characteristic ear deformations are frequently observed in horseshoe bats (Rhinolophidae). In these animals, the pinna changes regularly between an upright and a bent configuration. In the bent configuration, the tip of the pinna tilts forward, down, and sideways, changing the curvature of large portions of the ear surface. Entire deformation cycles can be completed in as little as 200 ms. The time-variant geometry of the pinna deformations in the greater horseshoe bat (Rhinolophus ferrumequinum) was captured with a stereo pair of high-speed video cameras. Landmark points were marked on the pinna with dyes that were equally visible in the video frames as in x-ray micro-CT. The CT model was matched to the locations of the landmarks in the deforming ears inferred from stereo reprojection. Numerical predictions were obtained for the acoustic behavior of ear shapes at different phases during the deformation cycle. It was found that the pinna deformations seen in the animals can produce large changes in the directivity patterns. [Work supported by NSFC (Project No. 10774092) and CSC.]