Abstract
Based on the characteristics of the ultrasounds they produce, echolocating bats can be categorized into two main types: broadband FM (frequency modulated) and narrowband CF (constant frequency) echolocators. In this study, we recorded the echolocation behavior of a broadband FM (Pipistrellus abramus) and a narrowband CF echolocator species (Rhinolophus ferrumequinum nippon) while they explored an unfamiliar space in a laboratory chamber. During flight, P. abramus smoothly shifted its acoustic gaze in relation to its flight direction, whereas R. ferrumequinum nippon frequently shifted its acoustic gaze from side to side. The distribution of the acoustic gazes of R. ferrumequinum nippon was twice as wide as that of P. abramus. Furthermore, R. ferrumequinum nippon produced double pulses twice as often as P. abramus. Because R. ferrumequinum nippon has a horizontal beam width (−6 dB off-axis angle) half as wide (±20.8 ± 6.0°) as that of P. abramus (±38.3 ± 6.0°), it appears to double the width of its acoustical field of view by shifting its acoustic gaze further off-axis and emitting direction-shifted double pulses. These results suggest that broadband FM and narrowband CF bats actively control their acoustic gazes in a species-specific manner based on the acoustic features of their echolocation signals.
Highlights
Echolocating bats are acoustically guided animals that emit ultrasound pulses and perceive space by analyzing the returning echoes, a form of active sensing without visual input
Because R. ferrumequinum nippon has a horizontal beam width (−6 dB off-axis angle) half as wide (±20.8 ± 6.0°) as that of P. abramus (±38.3 ± 6.0°), it appears to double the width of its acoustical field of view by shifting its acoustic gaze further off-axis and emitting direction-shifted double pulses
These results suggest that broadband FM and narrowband constant frequency (CF) bats actively control their acoustic gazes in a speciesspecific manner based on the acoustic features of their echolocation signals
Summary
Echolocating bats are acoustically guided animals that emit ultrasound pulses and perceive space by analyzing the returning echoes, a form of active sensing without visual input. Rhinolophidae, Hipposideridae, and some species of Mormoopidae are narrowband constant frequency (CF) echolocators, emitting long calls dominated by a single CF separated by brief periods of silence (i.e., high duty cycle, HDC) (Fenton et al 2012). Narrowband CF bats employ Doppler-shift compensation (DSC), adjusting the frequency of their calls to maintain echo frequency within the acoustic fovea, avoiding masking effects using frequency to separate pulses and their echoes (Schnitzler 1968; Schnitzler and Denzinger 2011). J Comp Physiol A (2016) 202:791–801 silence between them, using time rather than frequency to separate pulses and echoes and avoid masking effects (i.e., low duty cycle, LDC). Narrowband CF and broadband FM echolocation differ in a number of respects, and bats from each group are thought to adapt their acoustic and flight behaviors according to their foraging habitats (Simmons and Stein 1980; Neuweiler 1984; Fenton 2010, 2013)
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