The question of whether bats are loud is nuanced, depending on the specific sounds produced and the listener’s auditory capabilities. While some bat vocalizations are beyond human perception, other sounds they make are within our hearing range, revealing a complex acoustic world.
Beyond Human Hearing: The World of Bat Sounds
The vast majority of sounds bats produce are ultrasonic, meaning they exist at frequencies exceeding the upper limit of human hearing, typically above 20 kilohertz (kHz). These high-frequency sounds are central to echolocation, a sophisticated biological sonar system bats use for navigating and hunting in darkness. Bats generate these sounds through their larynx, emitting pulses that bounce off objects. By interpreting the returning echoes, bats can construct a detailed “acoustic image” of their surroundings, discerning object characteristics and movement.
Bat echolocation calls vary widely in frequency, ranging from approximately 9 kHz to over 200 kHz. These calls can be remarkably intense, with some species emitting sounds exceeding 135 decibels (dB), comparable to the loudness of a smoke alarm. Despite their intensity, these sounds remain inaudible to humans because their frequencies are simply too high for our ears to detect.
What Sounds Do Humans Hear?
The typical range of human hearing spans from about 20 hertz (Hz) to 20 kHz. Since most bat echolocation calls are ultrasonic, they fall outside this audible spectrum. Our auditory systems are simply not equipped to process these high-frequency sounds.
However, there are specific circumstances where humans might perceive faint sounds from bats. Some larger bat species, or those that utilize lower-frequency echolocation, may produce calls that are at the very edge of human hearing. These can sometimes be heard as subtle clicks, rustling, or high-pitched squeaks, especially when bats are in close proximity. The Spotted Bat (Euderma maculatum), for example, is one species whose echolocation calls can be faintly audible to humans. Similarly, Pallid Bats (Antrozous pallidus) may lower their call frequencies into the human hearing range when in the vicinity of maternity roosts.
Why Bats Make Audible Sounds
Beyond echolocation, bats produce a diverse array of vocalizations that are within or near the human hearing range, serving various communicative purposes. These audible sounds are primarily social calls used for communication within their colonies. Bats employ these vocalizations for mother-pup recognition and for mating calls to attract partners.
Other social calls serve as warning signals to alert group members to threats or to defend territories. Bats also emit distress calls when they are captured or feel threatened. These distress signals can attract other bats or deter a predator. Additionally, sounds associated with roosting, such as rustling, scratching, or chattering, can be audible to humans if bats are residing in enclosed spaces. While many social calls are also ultrasonic, bats sometimes use lower frequencies for these communications to increase their broadcast range.