A comparative study of Pinna motions in horseshoe bats and old world leaf-nosed bats

Abstract

Horseshoe bats (Rhinolophidae) and Old World leaf-nosed bats (Hipposideridae) are two closely related bat families that stand out for the dynamics of their ears during biosonar behaviors. In bats belonging to both families, the outer ears (pinnae) can undergo substantial, fast, and non-rigid shape changes while the animals emit their biosonar pulse trains. So far, characterization of these motions has been limited to either very general measures (e.g., of overall ear rotation) and/or limited data sets covering only a single species. Here, we have combined high-speed stereo vision with digital animation techniques to reconstruct and compare the motions of the pinnae and the head in one rhinolophid (Rhinolophus ferrumequinum) and two hipposiderid species (Hipposideros armiger and Hipposideros pratti). In parallel, we have also recorded the pulses and echoes received by the animals. We found that the pinna motions in both families frequently overlap in time with the arrival of the echoes, so they could have a functional relevance for echo reception. The pinna motions were found to follow similar patterns in all three species and could be decomposed into three main components. Beyond these fundamental similarities, there were also pronounced quantitative differences between the motions seen in the two families.