Bats navigate and thrive in darkness using sound, a world often hidden from human perception. While some vocalizations are audible, much acoustic activity occurs at frequencies beyond human hearing. Understanding how bats use sound provides insight into their adaptations for nocturnal life.
Sounds Humans Can Hear
Bats produce vocalizations within our hearing range. These are typically social calls, rather than those used for navigating or hunting. They include chirps, squeaks, or chittering noises, often heard when bats are active around their roosts at dusk or dawn.
These audible sounds serve various communication purposes within bat colonies. They include distress calls from individuals, territorial warnings, or specific vocalizations between mother bats and their pups.
The Unheard World of Bat Sounds: Echolocation
Echolocation, also known as biosonar, allows bats to perceive their surroundings in the dark using the ultrasonic range. This process involves bats emitting high-frequency sound waves and then listening for the echoes that bounce back from objects in their environment.
Bats generate these ultrasonic pulses through their larynx or nostrils, with frequencies typically ranging from 14,000 to over 100,000 Hz, far exceeding the human hearing limit of 20,000 Hz. By interpreting returning echoes, bats construct a detailed sonic map, discerning an object’s distance, size, shape, and even its texture and movement. This system’s precision enables some bats to detect objects as fine as a human hair.
The Purpose Behind the Sounds
Bat sounds serve distinct and specialized functions for their survival and social structure. Echolocation calls are primarily used for navigation and foraging. This biosonar system is particularly effective for hunting prey, as bats pinpoint their exact location by rapidly increasing their call rate as they close in, known as a “feeding buzz.”
Beyond echolocation, audible social calls play a different role in bat interactions. These sounds facilitate communication within colonies, establishing social hierarchies and coordinating group activities. Mother bats use calls for recognizing their pups, and bats may use vocalizations to signal their location to other group members. Some male bats produce songs to attract mates or deter rivals.
Tools for Listening to Bats
Special equipment is needed to make bat sounds audible to humans. Bat detectors are devices designed to convert these high-frequency sounds into frequencies that fall within our hearing range. These portable tools contain specialized microphones capable of picking up ultrasonic signals.
Different types of bat detectors employ various methods to achieve this conversion. Heterodyne detectors work by mixing the incoming ultrasonic signal with an internal frequency, producing an audible “beat” frequency that humans can hear. Frequency division detectors divide the bat call’s frequency by a set factor, typically ten, into the audible range. Time expansion detectors record short bursts of ultrasonic sound and then play them back at a much slower speed, making the details of the calls discernible. These tools allow enthusiasts and researchers to identify bat species based on their unique call patterns and study nocturnal behaviors.