Bats are often depicted as creatures that “scream,” sparking curiosity about the sounds they truly make. The reality of bat vocalizations is more intricate than a simple scream, encompassing a range of sounds, many imperceptible to human ears. While some calls are loud, understanding their context and purpose reveals a sophisticated acoustic world.
The Sounds We Cannot Hear
Bats primarily navigate and hunt using echolocation, a remarkable biological sonar system. This process involves emitting high-frequency sound pulses and interpreting the echoes that return from objects in their environment. These sounds are “ultrasonic,” meaning their frequencies are above the typical range of human hearing, which extends up to about 20,000 Hertz (Hz) or 20 kilohertz (kHz).
Bat echolocation calls can range from approximately 9 kHz to 200 kHz, with many species operating well beyond our auditory capabilities. While we cannot hear these vocalizations, they are quite loud at their source. Some bats, often described as “shouters,” produce sounds comparable to the loudness of a smoke alarm. These high-pitched vocalizations are their way of acoustically “seeing” their surroundings, allowing them to detect objects as fine as a human hair and navigate in complete darkness.
The Sounds We Can Hear
Beyond their inaudible echolocation calls, bats also produce sounds that fall within the spectrum of human hearing. These audible vocalizations are distinct from their hunting sonar and serve primarily as social communication. They include a variety of chirps, clicks, and squeaks, particularly noticeable when bats are in their roosts or interacting with one another. These social calls play diverse roles, such as communication between a mother and her pup, signaling distress, or during courtship and territorial disputes.
Why Bats Are So Loud
The intensity of bat vocalizations, particularly their echolocation calls, is remarkable. Many bats produce sounds that can reach high decibel levels, with some species, like the bulldog bat, producing calls around 137 decibels (dB) at a distance of 10 centimeters. This level is significantly louder than a home smoke detector, which typically measures around 108 dB, or even a rock concert.
This extreme volume is a necessity for effective echolocation. High-frequency sounds, while providing detailed information, diminish quickly as they travel through the air. To ensure the sound waves can reach distant objects, like a tiny moth, bounce off, and return with enough clarity for the bat to process, they must be emitted at a very high initial volume. This allows the bat to receive detectable echoes, forming a precise acoustic map of its environment for successful navigation and prey capture.