Scientists have found that Japanese horseshoe bats living together in crowded colonies solve the noisy sonar problem by gradually changing their echolocation calls to match each other’s frequency.

Bats rely on echolocation to navigate in the dark and hunt insects. They send out high-pitched sound waves that bounce off nearby objects and return as an echo, which helps them locate objects.But when many bats emit similar sound waves at the same time, their signals can overlap. It creates noise that may make it difficult for the bat to recognize the echoes of its calls.A new study published in the Journal of Comparative Physiology A was conducted by researchers from Doshisha University in Japan. Greater Japanese horseshoe bats have a unique way of dealing with this challenge, ScienceThese bats gradually modify their calls so that members of the same colony use approximately the same frequency.

Researchers say this helps the bats receive clearer echoes and better detect prey while 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 sight.They emit ultrasonic calls, which are too loud for humans to hear. These sound waves hit insects, trees, cave walls, and other objects before bouncing back. By listening to these returning echoes, bats can tell where an object is, how far away it is, and even whether it is moving.

Scientists also study echolocation in bats because it has inspired improvements in sonar systems and sensor technology used in robots and other devices.

Echolocation is different

Most bat species use vocal calls that change in frequency during each call. However, the greater Japanese horseshoe bat is different. According to the research, their calls include both variable frequencies and a long segment that stays at a roughly constant frequency, which helps bats detect small changes in echo.Bats also have a highly specialized auditory system that is highly sensitive to a narrow range of sound frequencies. This allows them to observe very small differences in the return echoes.

It also compensates for the Doppler shift. This happens when the bat or its target moves which changes the frequency of the returning sound slightly. By tuning their calls, bats ensure that returning echoes stay within the frequency range where their hearing is most sensitive.

When many bats use similar calls

The researchers wanted to understand what happens when several horseshoe bats with slightly different call frequencies live together. To do this, they studied wild Japanese horseshoe bats that had been brought into captive colonies of the same species.They measured the bats’ echolocation frequencies before they entered the colony. They measured them again after they had spent about one month living with other bats.The study used data collected from 2008 to 2024. The researchers recorded bats from 15 different capture events during this period.The researchers found that the bats did not spread out their call frequencies to avoid interference, but rather moved slowly toward a common frequency.This was especially true for bats whose calls began at low frequencies. These bats increased their call frequencies after joining the colony, while bats that already used higher frequencies barely changed.Also, 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”

The researchers believe that 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 range of frequencies where important echoes from moving insects can stand out more clearly.Scientists compare it to trying to hear someone talking in a noisy room. If the sound one wants to hear is in a part of the audio range where there is less background noise, it becomes much easier to understand.For horseshoe bats, the quieter frequency range allows them to detect echoes of fluttering insects more reliably.Low-frequency bats benefited the most by shifting their calls upward. Without this modification, echoes returning from prey could interfere with the bat’s high-frequency calls.By moving to a higher frequency, these bats reduced this conflict, while keeping their prey’s echoes within their clearer listening range.