Bats are highly vocal mammals that rely extensively on sound to perceive their world and communicate with each other. Their vocalizations serve multiple purposes within their colonies and while navigating the dark. If you have heard a distinctly high-pitched shriek or squeak from a bat, it is likely a form of communication intended for other bats.
The Dual Nature of Bat Vocalizations
Bat sounds fall into two primary functional categories: echolocation calls and social communication calls. Echolocation is a sophisticated biological sonar system that allows bats to navigate and hunt in complete darkness. To achieve this, bats emit rapid, high-frequency sound pulses, often between 20 kilohertz (kHz) and 100 kHz, or even up to 200 kHz for some species.
These echolocation sounds are typically above the limit of human hearing, which generally cuts off around 20 kHz. For example, the loud pulses used by “shouting bats” like the Big Brown Bat can reach intensities of 110 decibels, comparable to a smoke alarm, but their ultra-high frequency makes them inaudible to us. This high frequency is necessary because shorter wavelengths provide the precision needed to detect tiny insects.
In contrast to the highly specialized echolocation pulses, bats also produce a wide repertoire of social vocalizations. These communication calls are generally lower in frequency, which is why some of them fall within the range humans can hear. Social calls are used for interaction between individuals within a colony, such as communicating territory, status, or to mediate conflicts.
These social sounds are often described as chirps, squeaks, and squawks. They tend to have longer durations and a less tonal quality compared to the rapid, rhythmic clicks of echolocation. Echolocation paints a picture of the physical environment, while social calls transmit information about the bat’s internal state or intent toward another bat.
When and Why Bats Produce Audible “Screams”
The sound that humans perceive as a bat “scream” is a high-intensity social call used in specific, heightened contexts. These audible shrieks are distinct from the rapid, high-frequency clicks used for navigation. The most common motivation for these loud, lower-frequency sounds is a response to distress.
When a bat is captured, threatened by a predator, or otherwise physically restrained, it will often emit an intense distress call that can be heard clearly by humans. This “screaming” may serve to startle a potential predator or alert nearby colony members to the danger.
Aggression is another primary context for these loud, audible vocalizations. Bats in a roost frequently dispute over roosting spots, food, or mating access. These interactions involve agonistic calls that sound like chattering, squabbling, or shrieks to the human ear.
Certain species produce complex songs during mating rituals, which can sometimes include audible components. Infant isolation calls, used by young bats to summon their mothers, are also part of the social repertoire and can be heard as high-pitched chirps or squeaks. These louder social calls fall into the lower end of the bat’s overall frequency range, often around or below 20 kHz, making them audible to humans.
Decoding the Sound: What Humans Can Hear
The reason most bat sounds are silent to us is directly related to the physical limits of the human auditory system. A healthy young person can typically hear sounds ranging from about 20 Hertz (Hz) up to 20 kHz. Since the majority of a bat’s echolocation calls are ultrasonic—meaning they are above 20 kHz—they simply do not register in our ears.
The sounds we do hear, the chirps, shrieks, and squeaks, are the lower-frequency social calls. These vocalizations are produced in the 10 kHz to 20 kHz range, which falls just within the upper limits of our hearing capacity. Human hearing sensitivity to high frequencies naturally decreases with age, meaning many adults can hear little to nothing above 15 kHz.
Consequently, a child or young adult is more likely to hear the higher-pitched social calls than an older adult, whose upper frequency limit has dropped. In rare cases, a few bat species, such as the Spotted Bat, produce echolocation calls that dip down close to 20 kHz, which can be faintly audible to people with exceptionally good hearing.