Bats are highly vocal mammals, constantly producing sounds that serve two distinct purposes: navigation and social communication. The noises they generate fall into two broad categories, which explains why most people rarely hear them. The majority of bat sounds are high-frequency, ultrasonic pulses used to create an acoustic map of their environment. They also produce a rich repertoire of lower-frequency social calls that help govern their complex colony life. These vocalizations allow bats to thrive in darkness and maintain sophisticated social structures.
The Ultrasonic Language of Echolocation
Echolocation is the primary function of bat sound production, acting as a sophisticated biological sonar system that allows them to “see” with sound. The process involves the bat generating high-frequency sound pulses, often between 15,000 and 150,000 Hertz, and then precisely listening for the returning echoes. Most species produce these pulses by passing air over specialized vocal cords in the larynx, emitting the sound through the mouth or, in some cases, the nose.
The echoes that bounce back from objects provide the bat with detailed information about the location, size, texture, and movement of everything in its path. For hunting, the acoustic data is so fine-tuned that some bats can detect objects as thin as a human hair. When a bat closes in on its insect prey, the rate of sound emission rapidly increases, transitioning into a “feeding buzz” for the final capture.
Shorter wavelengths provide higher resolution, allowing the bat to form a detailed acoustic image. The bat’s brain processes the time delay between the pulse and the echo within milliseconds, enabling split-second decisions during rapid flight. This acoustic system is indispensable for insectivorous bats, guiding them through complete darkness to forage and navigate safely.
The Social Sounds of Bats
Beyond the navigational function of echolocation, bats possess a complex auditory language for communicating. These social vocalizations encompass a wide array of sounds, including complex songs, chirps, squeaks, and screeches. These calls are employed to maintain colony cohesion and facilitate daily life.
Specific calls convey alarm and distress, while others are used during territorial disputes. Male bats in certain species, such as the Mexican free-tailed bat, produce intricate songs for courtship and to defend their roosting territories. In large colonies, mother-infant communication is critical, with young bats emitting isolation calls that allow the mother to locate her pup.
Some social sounds, like the agonistic “squawking” of big brown bats, fall within the upper range of human hearing. While many social calls are still ultrasonic, their function is purely communicative. Echolocation calls can carry social information, allowing bats to identify individuals or alert nearby foragers to a potential food source.
Why Most Bat Noises Go Unheard
Most bat noises escape human detection due to the physiological limits of the human auditory system. The typical hearing range for a healthy young adult spans from approximately 20 Hertz up to 20,000 Hertz (20 kHz). Any sound frequency above this upper limit is classified as ultrasound.
Since most bat echolocation calls operate at frequencies far exceeding 20 kHz, they are imperceptible to the human ear. Some species call as high as 150 kHz, several times higher than the highest pitch a person can perceive. This high frequency makes the vast majority of their acoustic world silent to us.
The frequency barrier is compounded by the classification of bats into microbats and megabats. Microbats, which constitute the majority of bat species, rely heavily on high-frequency laryngeal echolocation. In contrast, most megabats (fruit bats) do not use laryngeal echolocation, relying instead on sight and lower-frequency social calls.
The few bat noises a person might hear, such as a faint click or a high-pitched chatter, are typically the lowest-frequency echolocation calls of a close-flying bat or one of their lower-frequency social calls. Specialized equipment, known as bat detectors, must be used to translate the ultrasonic sounds into a lower, audible frequency for human analysis.