Sonar beam dynamics in leaf-nosed bats.

Meike Linnenschmidt,Lutz Wiegrebe

doi:10.1038/srep29222

Abstract

Ultrasonic emissions of bats are directional and delimit the echo-acoustic space. Directionality is quantified by the aperture of the sonar beam. Recent work has shown that bats often widen their sonar beam when approaching movable prey or sharpen their sonar beam when navigating through cluttered habitats. Here we report how nose-emitting bats, Phyllostomus discolor, adjust their sonar beam to object distance. First, we show that the height and width of the bats sonar beam, as imprinted on a parabolic 45 channel microphone array, varies even within each animal and this variation is unrelated to changes in call level or spectral content. Second, we show that these animals are able to systematically decrease height and width of their sonar beam while focusing on the approaching object. Thus it appears that sonar beam sharpening is a further, facultative means of reducing search volume, likely to be employed by stationary animals when the object position is close and unambiguous. As only half of our individuals sharpened their beam onto the approaching object we suggest that this strategy is facultative, under voluntary control, and that beam formation is likely mediated by muscular control of the acoustic aperture of the bats’ nose leaf.

Highlights

Phyllostomid bats, like rhinolophid bats, emit their signals through a pair of nostrils surrounded by a conspicuous nose leaf, which often extends at the top in the shape of a lancet
When object distance decreased from >1 m to 0 m, the median reduction in call level was 11.1 dB rms @0.1 m
Rows 2 and 3 of Fig. 2 show that the bats decreased the median inter-call interval by 36.8 ms and the median call duration by 0.3 ms while the ensonified object approached. Such adaptations in the temporal parameters of the echolocation activity with respect to object distance are known to avoid a temporal overlap between the returning echo and the following call emission

Summary

Introduction

Phyllostomid bats, like rhinolophid bats, emit their signals through a pair of nostrils surrounded by a conspicuous nose leaf, which often extends at the top in the shape of a lancet. Earlier studies with restrained phyllostomid bats in which the nose leaf was manipulated and modelling studies have shown that the nose leaf determines especially the vertical directionality[29,30] while the nostril spacing determines horizontal directionality[29] it has been suggested Macrophyllum macrophyllum can bend its nose leaf intentionally[31]. This would certainly affect the beam directionality. We quantify the extent to which nose-emitting bats (Phyllostomus discolor) show individual sonar beam dynamics and how they utilise such dynamics while ensonifying an approaching object

Methods

Results

Conclusion