What Do Bats Sound Like? The Unheard World of Echolocation

Bats navigate and interact with their environment in ways largely imperceptible to humans. While often associated with silent flight, bats are highly vocal animals, relying on diverse sounds for survival and communication. Many of these sounds occur at frequencies far beyond the human auditory range, yet are fundamental to their nightly activities and social structures.

The Unheard World: Echolocation

Bats primarily use echolocation, a biological sonar system, to navigate and hunt in complete darkness. They emit high-frequency sound pulses, often called ultrasound, typically above 20 kilohertz (kHz) and reaching up to 212 kHz, well beyond the average human hearing limit of 15-20 kHz. These sounds originate from the bat’s larynx and are typically emitted through the mouth or, in some species, through the nose.

Once emitted, these ultrasonic waves travel outwards and bounce off objects. Bats then listen for returning echoes, which provide detailed information about an object’s location, size, shape, and texture. By interpreting tiny differences in the echoes, bats construct a precise “sound map” of their surroundings, enabling them to avoid obstacles and locate prey with remarkable accuracy. The intensity of these calls can be loud, reaching up to 140 decibels, comparable to a rock concert, allowing the sounds to travel effectively for hunting in open spaces.

Bats adjust their echolocation calls based on activity. During a “search phase,” they emit calls at a lower repetition rate to broadly scan their environment. As they detect a potential target, they enter an “approach phase,” increasing the call rate for more precise information. When closing in on prey, the call rate becomes extremely rapid, forming a “terminal buzz” or “feeding buzz,” with up to 200 pulses per second, to pinpoint the exact location for capture. Different bat species also employ variations in their calls, such as frequency-modulated (FM) sweeps (rapid pitch changes) or constant frequency (CF) tones (steady pitch), each suited to specific hunting strategies and environments.

Beyond Echolocation: Social Calls and Other Sounds

While echolocation is essential for navigation and foraging, bats also produce other vocalizations, known as social calls. These sounds are used for communication within their colonies and serve diverse purposes. Social calls might include identifying individuals, defending territory, attracting mates, or warning other bats of danger.

These social calls often differ significantly from echolocation calls in frequency and structure. Some may occur at lower frequencies, occasionally audible to humans as squeaks, chirps, or squabbles, especially when bats are in close proximity within a roost. However, many social calls remain ultrasonic. Their less tonal quality and broad frequency distribution distinguish them from structured echolocation pulses.

How Humans Detect Bat Sounds

Most bat sounds, particularly echolocation calls, are ultrasonic and inaudible to humans. To study these soundscapes, researchers and enthusiasts rely on specialized bat detectors. These instruments convert high-frequency ultrasonic signals into frequencies audible to humans, typically between 120 hertz and 15 kilohertz.

Several types of bat detectors exist, each employing a different conversion method. Heterodyne detectors mix incoming ultrasonic bat calls with an internal frequency, producing an audible “beat” frequency. Frequency division detectors reduce the bat call’s frequency by a fixed factor, often dividing it by ten (e.g., a 55 kHz call becomes 5.5 kHz). Time expansion detectors record ultrasonic calls at a high sampling rate and play them back at a much slower speed, stretching the sound into the audible range for detailed analysis. By using these detectors, humans can “hear” the world of bats and gain insights into their behavior, species identification, and ecological roles.