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Cutting out the noise: How horseshoe bats adapt their echolocation behavior in colonies
Imagine searching for a gemstone in a dark cave: You use a flashlight, looking for a rainbow-colored glint in the darkness. Now, imagine 10 other people in the cave with you, using different-colored flashlights at the same time. Suddenly, you can no longer tell which light is coming from your gemstone, which light is from another flashlight or which light is coming from a reflection off another unknown object. That is what echolocation with multiple, overlapping frequencies would be like. But now, imagine if every person in the cave were using a flashlight of the same color. The glint from the gemstone would be much easier to see.
A new study reveals that greater Japanese horseshoe bats use a similar strategy: They align their echolocation call frequencies within a colony to avoid interference and better "see" their surroundings. The research is published in the Journal of Comparative Physiology A.
Bats are ecologically important, responsible for pest control, pollination and seed dispersal. They use echolocation to "see," emitting ultrasonic sound waves that bounce back off objects and give them an idea of what, where and how fast these objects are. Understanding bat echolocation is essential for revealing how animals perceive and navigate their environment. Moreover, bats' sophisticated sensing strategies have inspired advances in bio-inspired sensing technologies and autonomous robotic systems. For example, sonar technologies are constantly being improved based on observations from echolocating species like bats.
Most bats use frequency-modulated (FM) acoustic pulses; that is, they vary the frequency of single sound waves in their calls. However, some bat species, such as the greater Japanese horseshoe bat (Rhinolophus nippon), use unique pulses that include both FM and constant-frequency (CF) components. The bats detect and identify prey through "glints," periodic modulations in the amplitude and frequency of the reflected CF component of the echolocation call.
Additionally, these bats have a special anatomical feature called the acoustic fovea that shows exceptional sensitivity to a narrow frequency band centered on the second-harmonic CF component (CF2) of the echolocation pulse. CF-FM bats adjust the CF component of their echolocation calls to ensure that the CF2 component falls within the acoustic fovea to compensate for a phenomenon known as "Doppler shift," in which the frequency recorded by a moving observer or emitted by an object in motion changes based on speed and direction of motion.
A shared frequency for clearer echoes
Now, what happens when you mix a group of bats with overlapping CF2 frequency bands? This was the driving question behind the new study authored by Haruhito Matsumoto, Soshi Yoshida and Shizuko Hiryu of Doshisha University, which describes how wild greater Japanese horseshoe bats modify their CF calls in an unusual way when mixed with captive colonies.
"Unlike some other echolocating bats that separate their call frequencies to avoid interference, these horseshoe bats appear to converge on a shared frequency. 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," explains Dr. Yoshida.
As elucidated in previous work, a "silent spectral window" refers to a clutter-free band of frequencies above a given threshold that allows more effective sensing of prey. Here, the horseshoe bats adjust their echolocation frequencies so that most background acoustic interference remains below the threshold. Since Doppler-shifted acoustic glints from fluttering prey occur within this clutter-free frequency band, the silent spectral window enables reliable detection of these prey signals.
Wild bats shifted upward
For their study, the researchers captured wild horseshoe bats at 15 different time points and measured their CF2 frequencies. The bats were then introduced into a captive colony of the same species, and their CF2 frequencies were measured again after a month. From 2008 to 2024, data were collected from wild and captive bats across 15 capture events to obtain information on convergence.
Significantly, the researchers observed an asymmetric convergence pattern: Lower-frequency individuals, typically wild-caught bats, strongly shifted their frequencies upward during convergence. When there were no initial frequency differences between the wild and captive groups, no such convergence occurred. "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," Yoshida says.
A colony-level sensing advantage
The upward shift displayed by lower-frequency individuals supports the idea that convergence is a strategy employed by horseshoe bats to share a silent spectral window above the CF2 frequency. Essentially, when lower-frequency bats received their echolocation bounce-backs from prey (i.e., glints), they were in the same range as the higher-frequency calls of other bats in the colony. By shifting their frequencies higher, the lower-frequency bats could avoid that conflict. At the same time, the higher-frequency bats already enjoyed a clear window for their glints and had less incentive to adjust their calls.
Overlap in echolocation frequency is a major challenge for sensing in colonies of bats of the same species, but research on acoustic interference in mixed populations of same-species bats is scarce. This study helps fill that gap and provides new insight into how bats interact at an individual level and achieve high-sensory performance in echolocation.
Publication details
Haruhito Matsumoto et al, Greater Japanese horseshoe bats (Rhinolophus nippon) gradually converge their echolocation call frequency to colony members, Journal of Comparative Physiology A (2026). DOI: 10.1007/s00359-026-01821-5
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Citation: Cutting out the noise: How horseshoe bats adapt their echolocation behavior in colonies (2026, July 24) retrieved 24 July 2026 from https://phys.org/news/2026-07-noise-horseshoe-echolocation-behavior-colonies.html
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