Bats are fascinating creatures of the night, often perceived by humans through their high-pitched sounds, sometimes called “screeches.” These vocalizations are not random noises but serve crucial functions for their survival. These sounds allow them to navigate and communicate, enabling them to thrive in darkness.
Echolocation for Navigation and Hunting
The primary reason bats produce sounds is for echolocation, a sophisticated biological sonar system. Bats emit high-frequency sound pulses, known as ultrasound, which are typically beyond human hearing. These sound waves travel outward and bounce off objects, returning as echoes to the bat’s highly sensitive ears. By analyzing these echoes, bats construct a detailed “sound map” of their environment, allowing them to “see” in complete darkness.
Echolocation calls vary widely in frequency. The time it takes for an echo to return provides information about an object’s distance, while changes in the echo’s intensity and timing reveal details about its size, shape, density, and movement. This allows bats to deftly navigate through cluttered spaces, avoid obstacles, and locate tiny prey, such as flying insects, with remarkable precision.
When a bat detects prey, its echolocation strategy shifts. It increases the rate at which it emits calls, often referred to as a “feeding buzz.” During this final approach, the bat also reduces the outgoing energy of its calls, preventing the returning echoes from deafening itself as it closes in on the target. This rapid succession of calls provides continuous, updated information, allowing the bat to pinpoint and capture its meal efficiently.
Social Communication Among Bats
Beyond echolocation, bats use vocalizations for social communication within their colonies. These social calls are distinct from echolocation pulses and serve various purposes. Bats use them for warning about predators, territorial disputes, or attracting mates during breeding seasons.
Communication between mothers and their young is important. Mother bats produce “maternal directive calls” that resemble human “baby talk,” differing in pitch and timbre from sounds directed at other adults. These vocalizations help pups learn their species’ vocal repertoire and develop group-specific vocal signatures. These interactions highlight the intricate social structures within bat communities.
How Bats Produce Sounds
Bats generate vocalizations using the organ called the larynx, or voice box. This structure is adapted to produce the high-frequency sounds required for echolocation and social communication. Within the larynx, bats possess thin vocal membranes on their vocal folds. These membranes vibrate rapidly in the expiratory airstream, creating the ultrasonic sounds.
Sound emission varies among bat species. Many bats emit their echolocation calls through their open mouths. However, some species, like horseshoe bats, produce and direct their sounds through their nostrils, using nose-leaf structures to shape the sound beam. Laryngeal muscles allow bats to control the frequency and intensity of their vocalizations, adapting them for different environments and tasks.
Why We Hear Some Sounds and Not Others
Humans typically perceive sounds within a frequency range of 20 Hz to 20,000 Hz (20 kHz). Many bat vocalizations are ultrasonic, meaning their frequencies are well above this human hearing threshold. This is the primary reason why most bat sounds go unnoticed by the human ear.
While most bat sounds are inaudible, humans can sometimes hear certain bat vocalizations. These audible sounds are generally lower-frequency social calls, such as chirps, squeaks, or squawks, used for communication within a colony. Occasionally, the lower-frequency components of some echolocation calls may also be detectable if a bat is very close. Specialized devices called “bat detectors” can convert the ultrasonic calls into frequencies that humans can hear, allowing humans to hear them.