Everyone knows how your hearing is muffled after a noisy concert or working with heavy power tools, and terrestrial mammals are more susceptible to the temporary hearing loss associated with intense noise than fish or birds. But how does the hearing of the only airborne mammals – bats – bear-up in the perpetual noise that they generate as they echolocate to navigate their surroundings? Do they also suffer a reduction in hearing sensitivity while hunting in groups or when emerging from their roosts in great noisy swarms, when the noise can reach up to 140 dB SPL (sound pressure level)? Andrea Simmons, Kelsey Hom, Michaela Warnecke and James Simmons from Brown University, USA, decided to measure how the hearing of big brown bats (Eptesicus fuscus) is affected by exposures to loud noise [152 dB SEL (sound exposure level)] ranging in frequency from 10 to 100 kHz for an hour.
After measuring the normal hearing thresholds of bats, the team exposed the animals to an hour of loud noise and then repeated the hearing measurements 20 min, 2 h and 1 day later. Impressively, the bats suffered little, if any, hearing loss. ‘Our results are consistent with the hypothesis that big brown bats are less susceptible to noise-induced hearing losses than expected on the basis of broadband noise exposure data from other mammals’, say Simmons and her team. They add, ‘This decreased susceptibility may be related to the unique demands of echolocation, which requires foraging and navigating in the midst of intense noise soundscapes’, and they hope to learn how the bats protect their hearing in noisy situations that would temporarily deafen other mammals.