Scientists have found that Japanese horseshoe bats living in crowded colonies get around noisy sonar problems by gradually changing their echolocation calls to match each other’s frequencies
Bats rely on echolocation to move in the dark and hunt insects. They emit high-pitched sound waves that bounce off nearby objects and return as echoes, which help them determine the location of objects.But when many bats emit similar sound waves at the same time, their signals can overlap. It creates noise that makes it harder for the bats to recognize the echoes of their own calls.Researchers at Doshisha University in Japan published a new study in the Journal of Comparative Physiology A. According to Science X, Japanese horseshoe bats have a unique way of dealing with this challenge.These bats gradually adjust their calls so that members of the same group use nearly the same frequency.
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Researchers say this helps the bats receive clearer echoes and better detect prey when flying together.
How bats use sound to “see”
Bats are one of the few animals that rely primarily on echolocation. Since many species are nocturnal, they cannot always rely on vision.They emit ultrasonic calls that are too high for humans to hear. These sound waves hit insects, trees, cave walls and other objects and then bounce back. By listening to these returning echoes, bats can tell where an object is, how far away it is, and even whether it’s moving.Scientists also study bat echolocation because it has inspired improvements in sonar systems and sensing technology used in robots and other devices.
different echolocations
Most bats use acoustic calls, which vary in frequency with each call. The larger Japanese horseshoe bat, however, is different. According to the study, their calls include both changing frequencies and long segments that maintain an almost constant frequency, which helps the bats detect small changes in echoes.Bats also have highly specialized hearing systems that are extremely sensitive to a narrow range of sound frequencies. This allowed them to notice very small differences in the returning echoes.
Japanese giant horseshoe bat (Image source: I Naturalist)
They also compensate for “Doppler shift”. This happens when the bat or its target moves, which slightly changes the frequency of the returning sound. By adjusting their calls, bats ensure that the returning echoes stay within the frequency range to which their hearing is most sensitive.
When many bats make similar calls
Researchers wanted to understand what happens when many horseshoe bats with slightly different call frequencies live together. To do this, they studied wild greater Japanese horseshoe bats of the same species that were brought into captivity.They measured the bats’ echolocation frequencies before they entered the roost. After living with the other bats for about a month, they measured them again.The study used data collected from 2008 to 2024. The researchers recorded the bats at 15 different capture events during that period.The researchers found that rather than spreading their call frequencies to avoid interference, the bats slowly moved toward shared frequencies.This is especially true for bats that start their calls at a lower frequency. These bats increased their call frequency after joining the colony, while bats already using higher frequencies showed little change.Furthermore, this adjustment did not occur when wild and captive bats already had similar call frequencies before joining the colony.The researchers say this suggests bats only change their calls when there are clear differences between individuals.
“Quiet Spectral Window”
The researchers believe this shared frequency helps create a “silent spectral window.” When many bats call together, most of the background sounds stay below a certain frequency. This leaves a relatively quiet frequency range where the important echoes of moving insects can stand out more clearly.Scientists liken it to trying to hear someone in a noisy room. It’s easier to understand if the sound people want to hear is in a range of sounds with less background noise.For horseshoe bats, this quieter frequency range allows them to more reliably detect echoes from flapping insects.Bats with lower frequencies benefit the most from moving their calls upward. Without this adjustment, echoes returning from prey may overlap with high-frequency bat calls.By moving to higher frequencies, these bats reduce this conflict while still keeping their prey’s echoes within clearer listening range.
