The Two Main Types of Bat Sounds
Bats produce two primary categories of sounds, each serving distinct purposes. One main type is echolocation calls, which are high-frequency sounds that bats emit to navigate and locate prey in their environment. These sounds allow bats to construct a detailed “sound map” of their surroundings, providing information about obstacles and the movement of insects. Most echolocation calls are ultrasonic, meaning their frequencies are above the range of human hearing.
The other category is social calls, which bats use for communication. These sounds facilitate various interactions, including mating rituals, defending territories, and maintaining cohesion within a colony. Mother bats also use specific social calls to communicate with their offspring. While many social calls are also ultrasonic, some can fall within the range that humans can hear.
How Bats Create and Utilize Sound
Bats generate their sounds primarily through a specialized voice box, the larynx, which vibrates rapidly to produce sound waves. Depending on the species, these sounds are then emitted either through the bat’s mouth or through its nostrils. The sounds are produced in rapid, repetitive bursts, allowing for continuous environmental updates.
For echolocation, bats emit these sound waves and then interpret the echoes that bounce back from objects. The time delay between emission and reception of the echo provides information about an object’s distance. Variations in the intensity of the returning sound indicate the size and texture of an object, while shifts in frequency, known as the Doppler effect, reveal whether an object is moving towards or away from the bat. This process allows bats to detect, track, and intercept moving prey with precision, even in complete darkness. Social calls use similar vocal mechanisms, but their interpretation focuses on communicative content, enabling complex social interactions.
What Humans Can and Cannot Hear
Most bat sounds, especially echolocation calls, are ultrasonic, with frequencies too high for human ears. The typical human hearing range extends up to about 20 kilohertz (kHz), but many bat echolocation calls operate well above this threshold, sometimes exceeding 100 kHz.
However, certain bat social calls can fall within the range of human hearing. These audible sounds might manifest as faint chirps, squeaks, or clicks, especially if one is near a bat colony or if distressed. To overcome the limitations of human hearing, devices known as bat detectors convert high-frequency ultrasonic calls into lower, audible frequencies, allowing people to “hear” otherwise inaudible bat sounds.