Echolocation behavior in big brown bats is not impaired after intense broadband noise exposures

Abstract

Echolocating bats emit trains of intense ultrasonic biosonar pulses and listen to weaker echoes returning from objects in their environment. Identification and categorization of echoes are crucial for orientation and prey capture. Bats are social animals and often fly in groups in which they are exposed to their own emissions and to those from other bats, as well as to echoes from multiple surrounding objects. Sound pressure levels in these noisy conditions can exceed 110 dB, with no obvious deleterious effects on echolocation performance. Psychophysical experiments show that big brown bats (Eptesicus fuscus) do not experience temporary threshold shifts after exposure to intense broadband ultrasonic noise, but it is not known if they make fine-scale adjustments in their pulse emissions to compensate for any effects of the noise. We investigated whether big brown bats adapt the number, temporal patterning or relative amplitude of their emitted pulses while flying through an acoustically cluttered corridor after exposure to intense broadband noise (frequency range 10-100 kHz; sound exposure level 152 dB). Under these conditions, four bats made no significant changes in navigation errors or in pulse number, timing and amplitude 20 min, 24 h or 48 h after noise exposure. These data suggest that big brown bats remain able to perform difficult echolocation tasks after exposure to ecologically realistic levels of broadband noise.

Big brown bats (Eptesicus fuscus) successfully navigate through clutter after exposure to intense band-limited sound

“…In the experiment by Hom et al . 13 , neither the complexity of sonar sound groups nor the distributions of short and long IPIs varied before and after sound exposure. These data indicate that prior intense wideband sound neither impaired the ability to navigate by biosonar nor increased the perceptual difficulty of the task.…”

“…It is possible that the experimental parameters tested by Hom et al . 13 were not sufficiently sensitive to uncover any post-exposure impairments in behavioral performance or alterations in the temporal patterning of biosonar pulses. Indeed, many psychophysical studies of TTS in other terrestrial mammals have quantified decreases in hearing sensitivity after band-limited, rather than wideband, exposures and at shorter post-recovery times (2–4 min rather than 20 min 1 , 2 , 8 ).…”

“…Hom et al . 13 trained four big brown bats to fly down a narrow, curved corridor through a dense array of plastic hanging chains providing strong clutter echoes 14 , 15 similar to the complex acoustic reflectors bats encounter while navigating through vegetation 16 . Bats navigated the corridor accurately, with few errors, both before and 20 min after exposure to 1 hr of intense wideband sound (10–100 kHz, 116 dB SPL).…”

“…To determine whether the results of Hom et al . 13 could be replicated with different experimental parameters, we exposed bats to sounds of various bandwidths (BW) at the same duration (1 hr) as used in that experiment, but we increased the level of exposure to a mean level of 123 dB SPL and we assessed bats’ performance in navigating a denser chain array beginning at 2 min post-exposure. These exposure parameters are more comparable to those used in TTS experiments with other terrestrial vertebrates 1 , 2 , 8 – 10 .…”

Biosonar interpulse intervals and pulse-echo ambiguity in four species of echolocating bats

“…This basic chain configuration, but with either straight or curved corridors of varying widths, has been used previously to examine echolocation during flight (Petrites et al, 2009;Knowles et al, 2015;Wheeler et al, 2016). Because the task is a useful laboratory model for guidance in clutter, it also has been used to assess the effects of intense sound exposure on bats (Hom et al, 2016;Simmons et al, 2018). In the Brown University flight room, individual links in the chains measured 4.0 cm wide, 7.5 cm long and 1.0 cm thick.…”