Performance of Doppler shift compensation in bats varies with species rather than with environmental clutter

Abstract

The performance of vocal motor control is crucial for vocal communication; however, its evolution and ecological drivers are largely unknown. Doppler shift compensation (DSC), which has been found only in bats, represents an excellent model for studying the mechanisms and evolution of vocal control. We tested whether species that are more dependent on DSC for pulse–echo separation have a more precise DSC and whether changes in environmental clutter would result in adjustments in DSC performance. We recorded the echolocation and flight behaviour of the greater horseshoe bat, Rhinolophus ferrumequinum, and the great leaf-nosed bat, Hipposideros armiger, flying through a corridor and a window in turn. The DSC precision in H. armiger was significantly lower than that of R. ferrumequinum; the offset between the reference frequency and resting frequency, however, was not significantly different between the two species. We also studied the DSC of H. armiger flying through windows of different sizes. Their flight speed decreased significantly with reduced window size. However, DSC precision and the offset did not vary significantly with window size. Our results suggest that DSC is more precise in rhinolophids, which have a higher demand for pulse–echo separation by DSC, than in hipposiderids. Changes in environmental clutter do not necessarily result in adjustments of DSC performance. Functional importance associated with high-performance vocal control may be critical in shaping the precision of vocal control in the course of evolution. Instead, habitat clutter encountered by vocalizing animals may not play an important role.