Bats are mammals often misunderstood, especially regarding the sounds they produce. Unlike birds that chirp, bats do not. Instead, they generate a diverse array of sounds for navigating in darkness, locating prey, and communicating. These vocalizations are central to their survival and social structure.
Diverse Bat Vocalizations
Bats produce a broad spectrum of sounds, many beyond human hearing. These vocalizations fall into two main categories: echolocation and social communication. The term “chirp” is inaccurate for bats; their sound production and purpose differ significantly from a bird’s song. Instead, bats emit complex pulses of sound tailored to their environment and specific needs.
Echolocation: How Bats Navigate and Hunt
Echolocation, also known as biosonar, is a specialized ability allowing bats to “see” with sound, enabling navigation and foraging in darkness. Bats produce high-frequency sound pulses, primarily from their larynx, though some species emit them through their nostrils. These sounds, ranging from 9 kHz to over 200 kHz, bounce off objects, creating echoes that return to the bat’s tuned ears. By interpreting these echoes, bats construct a detailed “sound map” of their surroundings, determining an object’s distance, size, shape, texture, and movement.
As a bat approaches a target, like a flying insect, its call repetition rate increases, providing frequent updates on the prey’s location. This culminates in a rapid “feeding buzz” just before capture, with the bat emitting up to 200 pulses per second to pinpoint its prey. Echolocation calls can be frequency-modulated (FM), where pitch varies, or constant frequency (CF), where pitch remains stable. FM calls are excellent for precise range discrimination, suitable for navigating cluttered environments, while CF calls are better for detecting object velocity and movement, such as flapping insect wings, in open spaces.
Social Communication Among Bats
Beyond echolocation, bats use a variety of calls for social interactions within their colonies. These social vocalizations serve purposes such as:
Individual identification
Warning others of potential predators
Defending territory
Attracting mates
Bats also use specific calls for appeasement, promoting social contact, and communication between mothers and their young. Infant bats, for example, produce isolation calls enabling mothers to locate their pups within a large colony.
These social calls often differ from echolocation calls in frequency patterns and can be complex, showcasing sophisticated communication networks within bat communities. While primarily for orientation and hunting, echolocation calls can also carry social information like sex, age, and individual identity, which other bats may “eavesdrop” on. This shows that even their navigational sounds possess a communicative function.
Audibility of Bat Sounds to Humans
Most bat vocalizations, particularly high-frequency echolocation calls, are ultrasonic (above 20 kHz) and inaudible to humans. The human hearing range extends from 20 Hz to 20 kHz. However, some lower-frequency social calls, such as squeaks, chittering, or even some “chirps” made by baby bats, can occasionally be detected by humans, especially those with more sensitive hearing or in quiet environments.
To study these inaudible sounds, researchers use specialized bat detectors. These instruments convert ultrasonic signals into frequencies within the human hearing range, allowing identification and analysis of bat species based on unique call patterns. Loud echolocation calls can be as intense as a jackhammer, but their high frequency means they quickly diminish in intensity over distance.