Bats are nocturnal mammals, and the short answer to whether they make noise is yes. Their nighttime world is filled with vocalizations that serve different functions, from navigation to social interaction. These sounds differ greatly in frequency and purpose; some calls are completely silent to human ears while others are readily detectable.
Echolocation: The Inaudible Night Calls
The primary mechanism bats use to perceive their dark environment is a sophisticated biological sonar system known as echolocation. This process involves the bat emitting a high-frequency sound pulse and then analyzing the returning echo to build a detailed acoustic map of its surroundings. The sound waves are produced in the larynx and typically emitted through the open mouth or, in some species, through the nose.
The majority of these echolocation calls fall into the ultrasonic range, which is well above the 20 kilohertz (kHz) limit of human hearing. Most insectivorous bats, for example, produce calls with dominant frequencies between 20 kHz and 60 kHz, making them completely inaudible to an average person. These high frequencies are necessary because they have short wavelengths, which allows the sound to strike and reflect off small targets like flying insects. The bat can determine an object’s distance by measuring the time delay between the emitted pulse and the returning echo.
The structure of the calls varies depending on the bat’s activity and environment. Bats use Frequency Modulated (FM) calls, where the pitch rapidly sweeps downward, to gain precise information about the range and fine details of an object. Alternatively, Constant Frequency (CF) calls, which maintain a steady pitch, are used to detect the subtle movement of prey using the Doppler effect.
When a bat detects a target and begins its final attack sequence, it increases its call rate dramatically into a rapid series of pulses known as a “feeding buzz.” This accelerated calling, which can reach up to approximately 200 pulses per second, provides the bat with a continuous, high-resolution update on the prey’s exact location just before capture.
The effectiveness of echolocation is directly linked to the environment. Lower frequencies travel farther but provide less detail, while higher-frequency calls offer greater resolution but are quickly attenuated by the air. The bat constantly adjusts the specific frequency and pulse rate to optimize its ability to locate prey and avoid obstacles while flying at high speeds.
Social Chatter: The Noises Humans Hear
While navigation calls are mostly silent to us, bats also produce vocalizations for communication that often fall within the human hearing range. These sounds are referred to as social calls, fulfilling various communication needs within a colony or between individuals. These audible noises include chirps, clicks, buzzes, and squawks that convey social information.
These social calls are used in specific contexts, such as resolving territorial disputes between bats or communicating within the dense, dark environment of a roost. A mother bat may use a unique signature call to locate and identify her own pup among hundreds or thousands of others in a maternity colony. These audible sounds are complex and are thought to contain significant information about the bat’s emotional state, including distress, aggression, or contentment.
In rare instances, echolocation calls are audible to humans, particularly from species that use exceptionally low frequencies for their sonar. For example, the Spotted Bat (Euderma maculatum) emits echolocation clicks that are faintly audible to a keen human ear in a quiet environment. However, when a person hears distinct, loud noise coming from a bat, it is overwhelmingly likely to be a social call, a direct form of communication. The sounds we hear are the bat’s way of interacting with its social world, contrasting sharply with the silent, ultrasonic world it uses to fly and hunt.