Bats fill the night sky with a rich and varied acoustic repertoire, but most of it is pitched well above the range of human hearing. The majority of bat echolocation calls are ultrasonic, above 20 kHz, which makes them inaudible to us without special equipment.1Cell Press (Current Biology). Echolocation What you might catch on a quiet evening is a faint ticking or squeaking from certain species whose lowest-frequency calls dip into our audible range. But what is actually happening acoustically is far more complex than a few chirps, involving rapid-fire buzzes, frequency sweeps, tongue clicks, social chatter, and even deliberate sonar jamming of rivals.
How Bats Produce Their Sounds
Most bats generate echolocation calls in the larynx, but not the same way you produce your voice. Researchers filming Daubenton’s bat larynges at up to 250,000 frames per second found that echolocation calls are produced by vibrations of the vocal membranes, thin tissue structures distinct from the vocal folds used for lower-frequency social calls. In none of the experiments did the vocal folds themselves vibrate during echolocation; only the membranes did.2PubMed Central. Expand their vocal range by recruiting different laryngeal structures for echolocation and social communication This dual-structure system lets a single bat produce both the ultrasonic pulses it uses to navigate and the lower-pitched calls it uses to interact with other bats, all from the same larynx.
Not every bat uses its larynx to echolocate. Egyptian fruit bats produce sonar clicks by snapping their tongues against the palate. These tongue clicks are shaped into a directional beam that the bat can steer by shifting the position of its tongue along the side of its mouth, creating phase differences across what functions as a small array of sound sources.3PLoS Biology. Tongue-driven sonar beam steering by a lingual-echolocating fruit bat Remarkably, this ability appears to be present from birth. Newborn pups of tongue-clicking species can steer their echolocation beams on their very first day of life, shifting the beam between left and right in patterns that follow the adult steering sequence about 60% of the time.4PubMed Central. Hearing, echolocation, and beam steering from day 0 in tongue-clicking bats
The Hunting Soundtrack
If you could slow down and pitch-shift the echolocation of a hunting bat, you would hear a dramatic three-act sequence. In the search phase, the bat emits calls at a relaxed pace, sometimes only a few pulses per second, sweeping for potential targets. Once something of interest shows up in the returning echoes, the bat transitions to the approach phase, gradually increasing its call rate and shortening each pulse to get finer spatial detail. The finale is the terminal buzz, a burst of calls so rapid it sounds like a continuous hum. Emission rates during this final buzz can reach 180 pulses per second or higher, packed into such a short window that each individual call lasts only a fraction of a millisecond.5PubMed Central. Fast sensory-motor reactions in echolocating bats to sudden changes during the final buzz and prey intercept
Researchers studying the Japanese large-footed bat have found that what happens immediately after the buzz is just as telling as the buzz itself. After a successful capture, the bat pauses for roughly 200 milliseconds before resuming normal calling. After a miss, the pause is shorter, around 114 milliseconds. When the bat catches prey but then drops it, the pause falls in between at about 153 milliseconds.6PubMed Central. Discriminating predation attempt outcomes during natural foraging using the post-buzz pause in the Japanese large-footed bat, Myotis macrodactylus These differences are reliable enough that researchers can determine whether a bat caught its meal just by listening to the timing of the post-buzz silence. It is a neat illustration of how much information is embedded not only in the sounds bats make, but in the gaps between them.
Whispering Bats
Not all bats broadcast at full volume. Some species are acoustic whisperers, calling at intensities so low that their sonar barely reaches a few meters. The brown long-eared bat emits echolocation calls at roughly 92 decibels measured close to its mouth, even while flying in open space where louder calls would seem advantageous.7PubMed Central. Calibrated microphone array recordings reveal that a gleaning bat emits low-intensity echolocation calls even in open-space habitat That sounds loud by everyday standards, but sound pressure drops steeply with distance, and ultrasonic frequencies fade even faster in air. By the time these calls have traveled a meter or two, they are extremely faint.
Hemprich’s long-eared bat takes whispering even further, calling at approximately 80 decibels. This desert-dwelling species hunts scorpions, and it detects them not through echolocation at all but by listening to the faint rustling of scorpion legs on sand.8PubMed. Hemprich’s long-eared bat (Otonycteris hemprichii) as a predator of scorpions: whispering echolocation, passive gleaning and prey selection Its quiet echolocation may exist mainly for navigation rather than prey detection.
Why whisper? One explanation involves an evolutionary arms race with prey. Many moths and other insects have ears tuned to ultrasound, and they perform evasive dives when they detect bat sonar. A quieter bat gives eared insects less warning. Researchers studying the brown long-eared bat have proposed, however, that its low-amplitude calling may not have evolved primarily as a stealth strategy. Instead, it could be a constraint imposed by the bat’s anatomy, with the small body and large ears limiting how loud a call the larynx can practically produce.7PubMed Central. Calibrated microphone array recordings reveal that a gleaning bat emits low-intensity echolocation calls even in open-space habitat The stealth benefit may be a happy accident rather than an evolved trait.
Social Calls and Mother-Pup Recognition
Echolocation gets most of the attention, but bats are also intensely social animals that use a separate set of vocalizations to communicate with each other. Social calls serve a wide range of purposes: deterring predators, chasing competitors away from feeding areas, attracting group members to roost sites, coordinating foraging, and courting mates.9Biological Reviews. Social communication in bats Many of these social calls sit at lower frequencies than echolocation pulses, which is why the sounds people occasionally hear from a nearby roost, squeaks, chattering, and high-pitched trills, tend to be social calls rather than echolocation.
One of the most precise uses of social vocalization is the acoustic bond between mothers and pups. In the crowded chaos of a maternity roost, where thousands of pups may hang clustered on a cave wall, a returning mother needs to find her own offspring among the masses. Asian particolored bat mothers can recognize the isolation calls of their individual pups, and pups older than about 12 days can distinguish their own mother’s echolocation pulses from those of unrelated females.10PubMed Central. Mutual mother-pup acoustic identification in Asian particolored bats The system works both ways, with each party learning and remembering the acoustic signature of the other.
Sonar Jamming
Not all bat-to-bat acoustic interactions are cooperative. Mexican free-tailed bats have been caught deliberately jamming the echolocation of competitors during aerial insect pursuits. When one bat closes in on a moth, a rival nearby emits a distinctive sinusoidal frequency-modulated signal, a wavering ultrasonic call that overlaps with the hunting bat’s terminal buzz and disrupts its ability to pinpoint the target. Playback experiments confirmed the effect: when researchers broadcast the jamming signal from a speaker, bats missed their targets significantly more often than when control sounds were played.11PubMed. Bats jamming bats: food competition through sonar interference This is not accidental interference from crowded airspace. The three-dimensional flight reconstructions showed extended interactions in which the jamming bat tracked and pursued its competitor, timing the disruptive signal to coincide with the critical final moments of the hunt.
Moths That Click Back
Bats are not the only ones making sounds at night. Some of their prey have evolved acoustic countermeasures. When certain moths detect incoming bat sonar, they produce their own bursts of ultrasonic clicks. This behavior has been documented across tiger moths, hawkmoths, and at least one geometrid moth species, making it far more widespread than scientists initially realized. The moth sounds serve multiple functions depending on the species: they can jam the bat’s sonar by flooding it with confusing echoes, signal to the bat that the moth is toxic and not worth eating, or simply startle the bat long enough for the moth to escape.12PubMed Central. Anti-bat ultrasound production in moths is globally and phylogenetically widespread Some non-toxic moths even mimic the clicks of their toxic relatives, bluffing their way out of being eaten.
The acoustic arms race between bats and moths has been running for tens of millions of years. A fossil bat from the Middle Eocene, roughly 50 million years old, already shows skull features consistent with advanced laryngeal echolocation, including an expanded cochlea and a long basilar membrane.13Current Biology. A Middle Eocene Stem Bat from France Helps Bridge the Gap between Archaic Stem Bats and Modern Bats That means insect prey has had an extraordinarily long time to evolve ears tuned to bat frequencies and acoustic tricks to fight back.
How Weather and Human Noise Reshape the Soundscape
What bats sound like on any given night depends partly on conditions they cannot control. Temperature and humidity both affect how quickly sound energy dissipates in air, and the relationship is not straightforward. Atmospheric attenuation increases with call frequency but is also shaped by temperature and humidity in complex, nonlinear ways. The result is that a bat call recorded on a warm, humid night may register different frequency content and apparent intensity than the same call on a cool, dry one, even if the bat has not changed its behavior at all.14PubMed Central. Weather conditions determine attenuation and speed of sound: Environmental limitations for monitoring and analyzing bat echolocation This has practical implications for anyone trying to survey bats acoustically, and it means that if you are listening for bats yourself, your chances of hearing the lowest-frequency edge of certain calls will vary from night to night.
Weather also influences when and how much bats call by affecting when they decide to fly. Research on insectivorous bats in central Chile found species-specific responses: some species started their nightly activity earlier on colder evenings, while others delayed departure until conditions improved. Humidity mattered too, with certain species more active on dry nights and others peaking at intermediate humidity. Mexican free-tailed bats stayed active later into the night when overnight temperatures remained warm.15PubMed Central. Species-Specific Responses of Insectivorous Bats to Weather Conditions in Central Chile If you are hoping to hear bats on a given evening, both temperature and humidity are worth paying attention to.
Human-generated noise introduces a different kind of challenge. Studies of Mexican free-tailed bats near natural-gas compressor stations found that bat activity at noisy sites dropped to roughly 60% of levels at quieter comparison sites. Low-frequency echolocators were hit even harder, with activity at the loudest locations falling to about a third of what was recorded at quiet sites. The bats that did persist at noisy locations adjusted their calls: pulse durations lengthened by about a millisecond, and bandwidth narrowed by about 600 hertz, as if the bats were concentrating their acoustic energy into a tighter frequency band to cut through the noise.16Global Ecology and Conservation. Anthropogenic noise alters bat activity levels and echolocation calls
Traffic noise produces similar adjustments. Lesser bulldog bats exposed to road noise changed the spectral and temporal characteristics of their echolocation signals and actually foraged longer, presumably because extracting useful echo information took more effort under noisy conditions.17PubMed. Traffic noise affects foraging behavior and echolocation in the Lesser Bulldog Bat, Noctilio albiventris (Chiroptera: Noctilionidae) Playback experiments with Mexican free-tailed bats showed that the type of noise matters: bats responded differently to traffic noise versus river noise, modifying call duration and frequency during river-noise playbacks in ways consistent with switching from foraging behavior to navigation behavior.18Ecosphere. Natural and anthropogenic noise shape bat activity and sonar behavior Bats, in other words, do not just tolerate noise passively. They actively retune their calls in real time, though at an energetic cost that may reduce hunting efficiency.
Identifying Bat Species by Sound Alone
Because different bat species produce calls with distinctive frequency ranges, durations, and sweep patterns, researchers can often identify which species is present using only acoustic recordings. A study of 22 bat species in Italy found that four species could be identified simply by measuring the frequency at which their call carried the most energy. For the remaining 18 species, a classification model using features like start frequency, end frequency, call duration, and the frequency of peak energy correctly sorted calls to the right species about 82% of the time. When the analysis was done at the genus level and included additional parameters, accuracy climbed to 94%.19Journal of Zoology. Identification of twenty‐two bat species (Mammalia: Chiroptera) from Italy by analysis of time‐expanded recordings of echolocation calls
Similar results have been reported elsewhere. Acoustic surveys in the forests of Hokkaido, Japan, correctly classified calls to one of seven species 92% of the time, with four species identified perfectly.20Zoological Science. Acoustic Identification of Eight Species of Bat (Mammalia: Chiroptera) Inhabiting Forests of Southern Hokkaido, Japan: Potential for Conservation Monitoring This approach has become a cornerstone of bat conservation monitoring, because you can leave an ultrasonic recorder in a forest overnight and learn which species are active there without ever handling an animal. The equipment needed ranges from relatively affordable handheld bat detectors that convert ultrasound into audible clicks in real time, to research-grade microphone arrays that can localize a bat in three-dimensional space and measure its call intensity at the source.
Those Oversized Ears
The sounds bats make are only half the equation. How they receive the returning echoes is just as specialized. Many bat species have conspicuously large, elaborately shaped ears, and the geometry is functional rather than ornamental. The external ear structures, including the small pointed flap inside the ear called the tragus, play a critical role in encoding the vertical position of a sound source. When researchers experimentally deflected the tragus in big brown bats, the animals’ ability to judge vertical angles degraded from a resolution of about 3 degrees to roughly 12 to 14 degrees. The mechanism works through a secondary echo: sound entering the ear bounces off the tragus and arrives at the ear canal on a slight delay after the direct signal. The length of that delay changes depending on the vertical angle the sound came from, and the bat’s brain reads that delay as positional information.21PubMed. Echolocation in bats: the external ear and perception of the vertical positions of targets
This is why many insectivorous bats have such ornate ear shapes, with ridges, furrows, and elaborate tragus structures. Each feature sculpts the incoming echoes in ways that give the bat’s auditory system more data about where in space a target is located. Species that rely heavily on passive listening rather than echolocation, like the scorpion-hunting Hemprich’s long-eared bat, tend to have especially large pinnae that act as parabolic collectors for faint prey-generated sounds. The ears, in a real sense, are as important to a bat’s acoustic world as the calls themselves.