Bats rely on echolocation to navigate in the dark and hunt insects. They send out loud sound waves that bounce off nearby objects and return as echoes that help them determine where things are.But when multiple bats send similar sound waves at the same time, their signals can overlap. This creates noise that makes it difficult for bats to recognize the echoes of their own voices.A new study published in the journal Comparative Physiology A by researchers at Doshisha University in Japan. Scientists have discovered that Japanese horseshoe bats have a unique way of dealing with this challenge, reports Science X.These bats gradually adjust their calls so that members of the same colony use approximately the same frequency.
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Researchers say this helps the bats receive clearer echoes and better locate prey when flying together.
How bats use sound to ‘see’
Bats are among the few animals that rely primarily on echolocation. Since many species are active at night, they cannot always rely on vision.They produce ultrasonic calls, which are too loud for humans to hear. These sound waves bounce off insects, trees, cave walls and other objects before bouncing back. By listening to these returned echoes, bats can determine where an object is, how far away it is, and even whether it is moving.Scientists also study bat echolocation because it has inspired improvements in sonar systems and sensing technology used in robots and other devices.
a different echolocation
Most bat species use sound calls whose frequency varies during each call. However, large Japanese horseshoe bats are different. According to research, their calls include both changing frequencies and a long segment that remains at a nearly constant frequency, which helps the bats detect small changes in echoes.Bats also have a highly specialized hearing system that is extremely sensitive to a narrow range of sound frequencies. This allows them to see very small differences in the returning echoes.
Japanese Greater Horseshoe Bat (Image Source: I Naturalist)
They also compensate for ‘Doppler shift’. This occurs when the bat or its target moves, causing the frequency of the returned sound to change slightly. By adjusting their calls, bats ensure that the returning echoes remain within the frequency range where their hearing is most sensitive.
When multiple bats use the same call
The researchers wanted to understand what happens when multiple horseshoe bats with slightly different call frequencies live together. To this end, they studied wild Greater Japanese Horseshoe bats that were introduced into captive colonies of the same species.They measured the echolocation frequencies of the bats before they entered the colony. After spending about a month with other bats, they measured them again.The study used data collected from 2008 to 2024. The researchers recorded bats from 15 separate capture events during this period.The researchers found that the bats did not spread out their call frequencies to avoid interference, but rather they gradually moved toward a shared frequency.This was especially true for bats whose calls began at lower frequencies. These bats increased their call frequencies after joining the colony, while bats already using higher frequencies had hardly any change.Furthermore, when wild and captive bats already had similar call frequencies before joining the colony, this adjustment did not occur.According to the researchers, this suggests that bats only change their calls when there is a noticeable difference between individuals.
‘silent spectral window’
Researchers believe this shared frequency helps create a ‘silent spectral window’. When several bats are speaking simultaneously, most of the background sounds remain below a certain frequency. This leaves a relatively quiet range of frequencies where important echoes from moving insects can stand out more clearly.Scientists compare it to trying to hear someone speaking in a noisy room. If the sound one wants to hear is in the part of the sound range where there is less background noise, it becomes much easier to understand.For horseshoe bats, this quieter frequency range allows them to more reliably detect the echoes of fluttering insects.Low-frequency bats benefited most from shifting their calls upward. Without this adjustment, echoes returning from hunting may overlap with high-frequency bat calls.These bats reduced that conflict by switching to higher frequencies, while still keeping their prey’s echoes within clear hearing range.