The Performance Of Doppler Shift Compensation In Echolocating Bats

The performance of vocal motor control is crucial for vocal communication.However,the evolution and the ecological drivers of the performance of vocal control 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.In flight,the bats lower the the frequency of their emitted pulses in order to compensate for Doppler shifts caused by flight movement.By DSC,the echo frequency can be kept constant around their sensitive hearing range,the echolocation pulse and echo information can be separated in different frequencies and the echolocating can be more accurately.The rapid audio-vocal feedback enables DSC bats to have a precise vocal motor control performance.The temporal overlap of the echoes with the outgoing pulses is a prerequisite for DSC in bats.The rhinolophids are more functionally dependent on DSC for pulse-echo separation than the hipposiderids due to their longer duration of echolocation pulses.However,it remains controversial whether hipposiderids have a lower DSC performance than the rhinolophids.Whether species that are more dependent on DSC for pulse-echo separation have a more precise DSC is unknown.In addition,highly cluttered backgrounds require bats to have high flight manoeuvrability and increase the difficulty of distinguishing echoes from background noise.Increased levels of environmental clutter may cause changes in the Doppler effects.When the rate of change in Doppler shifts is rapid,bats may not be able to keep pace,which will cause an increase in DSC error.Whether changes in environmental clutter would result in adjustments of DSC performance is also unknown.We recorded the echolocation and flight behaviour of the great leaf-nosed bat,Hipposideros armiger,and the greater horseshoe bat,Rhinolophus ferrumequinum,flying through a corridor and a window in turn.Under the same condition,the DSC precision,completeness,and the offset between reference frequency and resting frequency were compared to determine the DSC performance between rhinolophids and hipposiderids.Furthermore,we studied the DSC of H.armiger and R.ferrumequinum flying through windows with three different sizes in turn to determine the effect of environmental clutter on the DSC performance of bats.The main results were showed as follows:(1)The DSC precision in H.armiger(0.165%)was significantly lower than that of R.ferrumequinum(0.113%).Both species have a high DSC completeness and the offset between reference frequency and resting frequency was not significantly different between those two species.(2)As the size of window reduced,the success rate of H.armiger reduced and the flight speed decreased significantly.However,DSC precision,completeness and the offset of H.armiger did not significantly vary with the size of the window.In contrast,the success rate of R.ferrumequinum reduced while the flight speed appeared to increase first and then decreased as the window size reduced.The DSC precision,completeness and the offset of R.ferrumequinum vary significantly,but did not vary with the size of the window.This study suggests that DSC is more precise in rhinolophids,who 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,and the change in DSC performance of R.ferrumequinum may be related to physiological conditions such as body temperature.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.