Bats, the world’s only flying mammals, navigate and interact with their environment using sound. These vocalizations serve as their primary sensory system in the dark, replacing the reliance on sight common in most other mammals. Humans are curious about the sounds bats create, which range from high-pitched clicks to audible squawks heard near roosts. Understanding bat sound production requires exploring their unique biological adaptations.
Answering the Purring Question
Bats do not purr in the same biological way a domestic cat does. A feline purr is produced by the rhythmic contraction of the laryngeal muscles, causing rapid vibrations of the vocal cords during both inhalation and exhalation. This mechanism creates a continuous, low-frequency sound signaling contentment. Bats lack the specific laryngeal structure and muscular control required to sustain a purr throughout the respiratory cycle.
Some anecdotal accounts suggest hand-reared bats make a soft, contented rumbling sound when groomed or held. These sounds are often described as a purr because they express comfort. However, this vocalization is simply a low-amplitude chirp or a soft grind, not a true purr. The noises bats make are always functional calls, even when they convey a positive emotional state.
Echolocation: The Ultrasonic World
The most recognized vocal behavior bats employ is echolocation, a system used for navigation and hunting in darkness. This process involves the bat emitting high-frequency sound pulses and analyzing the returning echoes to form a “sound map” of its surroundings. Echolocation calls are ultrasonic, occurring at frequencies above human hearing, typically between 20 kilohertz (kHz) and 200 kHz.
The frequency and pattern of the call are tailored to the bat’s environment and activity. Bats foraging in open air use loud, lower-frequency calls, sometimes reaching 110 decibels, allowing the sound to travel further and scan a wide area. Conversely, bats hunting in cluttered forest interiors use quieter, higher-frequency calls for a more detailed, shorter-range picture, a technique sometimes called “whispering.”
Echolocation calls are categorized into constant frequency (CF) calls, which are steady in pitch, or frequency-modulated (FM) calls, which sweep across a range of pitches. CF calls detect the presence and velocity of a moving target, while FM calls provide information about the target’s location and texture.
When a bat detects prey, its repetition rate rapidly increases into a “feeding buzz,” a quick succession of calls for the final capture. This system allows bats to detect objects as fine as a human hair and is tailored to avoid the hearing range of certain prey, such as moths.
Social Calls: Audible Bat Language
Separate from navigation sounds, bats employ a variety of social calls for communication. These calls are often lower in frequency, with some falling within the human hearing range, which is why people sometimes hear bats squabbling near a roost. These vocalizations serve a communicative function similar to the chirps, growls, and meows of other mammals.
Social calls are structurally complex and tend to be atonal, lacking the consistent frequency of echolocation pulses. They are used in specific contexts, such as defending a territory or roosting site against intruders, often manifesting as harsh squawks. Bats also use these sounds during mating rituals to advertise their presence or assess a potential partner.
One important social function is the mother-pup bond, where specific “isolation calls” are used by pups to communicate their presence and need. This vocal signature allows mothers to locate their offspring within a dense, noisy colony. Scientists have identified distinct categories of social calls that vary in duration and complexity, ranging from simple short emissions to intricate, song-like sequences. These exchanges provide context for interaction and colony dynamics that echolocation cannot convey.