The audiograms of these species had similar overall shapes but differed substantially for frequencies below 9 kHz and in the frequency range of their echolocation calls. We measured their auditory brainstem responses to assess their hearing sensitivity. We present the hearing thresholds and echolocation calls of 12 different gleaning bats from the ecologically diverse Phyllostomid family. In this study, we investigate hearing in bats and how it shapes bat species coexistence. Understanding the coexistence of different foraging strategies, however, requires understanding underlying cognitive and neural mechanisms. So far, studies mainly have focused on the output of behavioral strategies of predators and their prey preference. Another important factor, however, is differences in sensory capabilities. Historically, research focused primarily on morphological and behavioral adaptations for foraging, roosting, and other basic ecological factors. Adaptations permitting niche differentiation enable species to coexist. The work was published in the Journal of Experimental Biology.Tropical ecosystems are known for high species diversity. “We hypothesise that the bat’s inner ear may have some special adaptations that allow it to protect itself from loud noises,” she says.įiguring out the mechanisms behind bats’ aural resilience is not just important for bat biology, but may provide inspiration to devices that better protect hearing for people in loud environments. So while the study shows that bats seem to take loud noises in their stride, it doesn’t explain how they do it – something Simmons and her team is working on at the moment. After 24 hours, the noisy group appeared to have improved their hearing sensitivity by 1.7 decibels. But neither did the bats who copped the noisy blast, and certainly none reached a six-decibel difference. Unsurprisingly, the ambient noise bats, on averge, did not lose any significant hearing sensitivity. A bat was deemed to have hearing loos, or “temporary threshold shift”, if the difference between the baseline and test scores was at least six decibels. Hearing tests were then conducted 20 minutes, two hours and 24 hours post-noise exposure. Two (Heisenberg and Dandelion) were taken to a different location and allowed to listen to an hour of ambient, but certainly not as loud, sounds.Īnother bat, Mellie, did both loudspeaker and ambient tests on separate occasions. Three (named Felix, Weezer and Boo) were then subjected to a loudspeaker blast spanning the entire hearing range of the bat for an hour. If they chose correctly, they received a mealworm treat. They did this by training the animals in a soundproof room to choose out of two speakers, one of which emitted a sound. So to see if big brown bats lost any hearing sensitivity following such loud noises, Simmons and her crew captured seven wild specimens and measured their baseline hearing. These “acoustically cluttered” conditions can reach levels of 140 decibels – comparable to being on the deck of an active aircraft carrier – for hours on end. Not only must they listen for the reflected sounds, which can return up to 80 decibels, but they must also contend with the din of the other bats flying in close proximity. Big brown bats emit intense pulses as loud as 120 decibels – about as loud as a rock concert or a sandblaster – to navigate and locate prey. In fact, after a day, their hearing seemed to improve.īats are some of the noisiest creatures. Neuroscientist Andrea Simmons and colleagues from Brown University in Rhode Island, US, tested the hearing of big brown bats ( Eptesicus fuscus) before and after an hour-long cacophony and found their hearing didn’t deteriorate. Transient deafness after sustained loud noise, while annoying, is a fact of life for us and other animals. We’ve all experienced muffled hearing following a concert or a day of using power tools.
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