Greater Japanese Horseshoe Bats Share Echolocation Frequencies in Colonies

Bats make rapid decisions every night in total darkness.

By interpreting echoes from calls they emit, they steer around obstacles, pursue insects and remain near other bats.

This may seem straightforward, yet it is considerably more difficult when dozens of bats are airborne together, all producing their own ultrasonic calls.

Scientists have discovered that one species tackles this challenge in an unexpected manner. Rather than separating their call frequencies to avoid each other, these bats commonly shift towards an identical frequency.

This collective strategy could enable them to locate prey more distinctly, despite the sound generated by an entire colony.

Bats use echolocation differently

Echolocation involves emitting high-frequency sound waves, then hearing the echoes reflected back.

These returning signals reveal the location of objects and their speed, and can even allow bats to find insects in flight. The impressive capability also provides inspiration for engineers developing sonar technology and autonomous robots.

While most bats continually alter the frequency of each call, greater Japanese horseshoe bats operate differently.

Each pulse contains both changing frequencies and a stable constant-frequency portion. This enables the bats to identify minute shifts in echoes, called glints, that indicate fluttering prey.

They additionally possess a specialised hearing characteristic known as the acoustic fovea. It is highly sensitive to a very narrow sound range centred on the second-harmonic constant-frequency element, called CF2.

As they fly, the Doppler effect alters the frequency of echoes returning to the bats. They therefore constantly modify their calls so those echoes remain within this exceptionally sensitive auditory range.

Unexpected patterns within bat colonies

Researchers Haruhito Matsumoto, Soshi Yoshida and Shizuko Hiryu, of Doshisha University, conducted the study.

They examined what occurs when wild greater Japanese horseshoe bats enter an established captive colony.

If separate groups naturally use distinct CF2 frequencies, would they increase the gap between them to limit interference, or would a different pattern emerge?

“Unlike some other echolocating bats that separate their call frequencies to avoid interference, these horseshoe bats appear to converge on a shared frequency,” said Yoshida.

“Building on our previous study showing that they use a ‘silent spectral window’ to detect Doppler-shifted echoes from fluttering prey, we propose that this convergence allows colony members to maintain and share that window.”

Identifying a quieter listening area

Previous work proposed the concept of a silent spectral window.

It is a relatively uncluttered frequency band above a particular threshold. It lets bats distinguish echoes from fluttering prey while reducing interference caused by other background sounds.

When the bats alter their calls so most unwanted sound remains below that threshold, they can more dependably detect the vital Doppler-shifted glints produced by insects.

Using similar call frequencies seems to preserve this clearer listening area throughout the colony.

Years of recordings of bat calls

The team captured wild horseshoe bats across 15 separate collection periods.

They recorded each animal’s CF2 frequency, brought the bats into a captive colony, then measured their frequencies again one month later.

Between 2008 and 2024, the researchers gathered information during 15 capture events involving wild and captive bats. The findings revealed an unequal response.

Bats with lower frequencies, generally the recently captured wild animals, increased their call frequencies far more than the higher-frequency bats altered theirs.

No such change occurred when the two groups began with closely matching frequencies.

“This observation was only possible because past and present laboratory members carefully recorded the calls of individual bats over many years. It highlights the scientific value of long-term data accumulated through sustained effort,” said Yoshida.

Why certain bats altered their calls

The increase in frequency supports the explanation that lower-frequency bats were attempting to prevent their prey echoes from overlapping with the higher-frequency calls already used by fellow colony members.

Raising their calls allowed these bats to retain returning prey echoes within the shared silent spectral window, rather than having them compete with background noise.

Higher-frequency bats already benefited from access to this more distinct listening range, so they had far less incentive to adjust their calls. This produced the unequal pattern observed during the study.

Understanding colony life

Although many studies have investigated bat echolocation, considerably fewer have considered what happens when individuals of one species with varying calling frequencies come together.

This study helps address that question, showing how individual bats adapt their behaviour to improve sensing while living in groups.

The results also contribute to the expanding understanding of how animals address difficult sensory problems.

As research into bat echolocation continues, findings of this kind could also inform future advances in sonar systems and other technologies intended to identify objects precisely in noisy settings.

The complete study appeared in the Journal of Comparative Physiology A.