Calibrated microphone array recordings reveal that a gleaning bat emits low-intensity echolocation calls even in open-space habitat

Abstract

Echolocating bats use ultrasound for orientation and prey capture in darkness. Ultrasound is strongly attenuated in air. Consequently, aerial-hawking bats generally emit very intense echolocation calls to maximize detection range. However, call levels vary more than tenfold (>20 dB) between species and are tightly linked to the foraging strategy. The brown long-eared bat (Plecotus auritus) is a primarily gleaning, low-amplitude species that may occasionally hawk airborne prey. We used state-of-the-art calibrated acoustic 3D-localization and automated call analysis to measure P. auritus’ source levels. P. auritus emits echolocation calls of low amplitude (92 dB rmsSPL re 20µPa @ 10cm) even while flying in open-space. While P. auritus thus likely benefits from delayed evasive manoeuvres of eared insects, we propose that low-amplitude echolocation did not evolve as an adaptive countermeasure, but is limited by morphological constraints.

Variation in echolocation call emission of Neotropical insect-eating bats in response to shifting ambient temperatures

“…We used this information to determine an appropriate bandpass filter for every recording session for final call analysis. We used the customdeveloped TOAD Suite software package (de Framond, Beleyur, et al, 2023;de Framond, Reininger, et al, 2023;Hügel et al, 2017;Lewanzik & Goerlitz, 2018) for MATLAB (Version R2007b; The Mathworks, Inc., Nattick (MA), USA) to calculate the bats' spatial position for each emitted signal based on the time-of-arrival differences (TOAD) from the central to the outer microphones of the array (Koblitz, 2018) and the speed of sound for the current air temperature and relative humidity.…”