Bats are nocturnal mammals known for their unique ability to navigate and hunt in darkness. While they produce sounds, only a fraction of their acoustic world is perceptible to human ears, as much of their communication and environmental sensing occurs at frequencies beyond our hearing range. Understanding the diverse sounds bats produce reveals how they interact with their environment and each other.
Sounds Humans Can Hear
Bats produce sounds audible to humans, such as chirps, clicks, and squeaks. These vocalizations typically serve social functions, including communication within a colony, mother-infant interactions, or distress calls.
One might hear these sounds if bats are roosting nearby, such as in an attic or a barn, where their social chattering can become noticeable. Disturbed bats might also emit audible distress calls. Beyond vocalizations, the rustling of wings as bats move within tight spaces or take flight can also be heard, providing another auditory clue to their presence.
The Unheard Sounds of Echolocation
The majority of bat acoustic activity involves ultrasound, frequencies too high for human ears to detect. The typical human hearing range extends up to 20 kHz, but bats produce sounds ranging from 9 kHz to over 100 kHz, sometimes up to 200 kHz. These high-frequency sounds provide superior resolution for detecting small objects. The shorter wavelengths of ultrasonic signals allow for more detailed echoes, useful for identifying tiny prey like insects.
Echolocation is the primary purpose of these ultrasonic calls, serving as the bat’s sensory system for navigating and hunting in darkness. These are the most common vocalizations bats produce. This reliance on ultrasound allows bats to construct a detailed “sound map” of their surroundings, even in environments with limited light.
How Echolocation Works
Echolocation operates by emitting sound waves and interpreting the returning echoes. Bats produce these high-frequency sound pulses from their mouths or, in some species, through their specialized noses. As these sound waves travel, they bounce off objects, creating echoes that return to the bat’s sensitive ears.
The bat’s brain rapidly processes these echoes to understand its surroundings. This includes determining the distance, size, shape, density, texture, and movement of objects or prey.
Bats modify their echolocation calls based on their environment. In open spaces, they might use lower-frequency calls that travel farther. In cluttered areas, they switch to higher frequencies for more detailed information.
When closing in on prey, bats increase their call rate dramatically, known as a “feeding buzz,” to precisely track the target. Different species also employ various call types, such as constant frequency (CF) calls for detecting moving objects or frequency-modulated (FM) calls for detailed environmental mapping, showcasing this adaptable sensory system.
Identifying Bat Sounds
Distinguishing bat sounds from other nocturnal animal noises can be challenging for the human ear. Audible chirps and clicks might sometimes be mistaken for insects or birds, especially when heard from a distance. However, specialized equipment known as “bat detectors” can reveal the inaudible world of ultrasonic bat sounds.
Bat detectors convert high-frequency ultrasonic calls into frequencies humans can perceive. Different types of detectors exist, such as heterodyne, frequency division, and time expansion, each with a unique method of making sounds audible. Using these devices, enthusiasts and researchers can hear bats and differentiate between species based on the unique patterns, frequencies, and repetition rates of their echolocation calls. Observing a bat’s erratic flight patterns at dusk, often a sign of foraging, also provides a visual clue that complements auditory identification.