Bats do not typically “chirp” during the day in the way birds do. Their vocalizations are primarily associated with their nocturnal activities, serving specialized functions like navigating in darkness and communicating with other bats. While some sounds might be heard in specific circumstances, bats are generally quiet during daylight hours.
Why Bats Don’t Chirp During the Day
Bats are predominantly nocturnal. This behavioral pattern allows them to avoid many diurnal predators, such as birds of prey, and access a rich supply of nocturnal insects. During the day, most bat species rest in sheltered locations, known as roosts, which can include caves, tree hollows, or even human-made structures like attics and bridges. This daytime roosting behavior is important for their safety and energy conservation.
While in their roosts, bats generally minimize activity and vocalizations to remain undetected. Although they might make some sounds if disturbed or when communicating within a large colony, these instances are not typical “day chirping.” Their metabolism and body temperature can drop significantly during the day in a state called torpor, similar to a mini-hibernation, further reducing their need for vocal output.
The World of Bat Vocalizations
Bats produce a diverse array of sounds, each serving a distinct purpose. These vocalizations fall into two primary categories: echolocation calls and social calls. Echolocation calls are specialized, high-frequency sounds used for sensing their environment. They enable bats to perceive their surroundings in the absence of light. Social calls facilitate communication between individual bats. These sounds are varied and can include chirps, clicks, buzzes, and whistles. Bats use social calls for various interactions, such as attracting mates, establishing and defending territories, and maintaining contact between mothers and their young within a colony. The type and frequency of these calls vary among species.
How Bats “See” with Sound
Echolocation is a sophisticated biological sonar system that allows bats to navigate and hunt in complete darkness. This process begins with the bat emitting high-frequency sound pulses, often referred to as ultrasound, from either its mouth or nose. These sound waves travel outward and, upon encountering an object, bounce back as echoes. The bat’s highly sensitive ears then receive and interpret these returning echoes. By analyzing the echoes, bats determine object characteristics like size, shape, texture, distance, and movement. For example, the time it takes for an echo to return indicates the object’s distance, while changes in the echo’s frequency can reveal if the object is moving toward or away from the bat. This precise auditory information allows bats to construct a detailed “sound map” of their surroundings, enabling them to avoid obstacles and accurately pinpoint prey, even objects as small as a human hair or a tiny insect. When hunting, bats increase the rate of their calls, producing what is known as a “feeding buzz,” to precisely track their target.
Sounds We Can Hear (and Why)
Most bat vocalizations, particularly their echolocation calls, are beyond the range of human hearing. Humans typically perceive sounds within a frequency range of approximately 20 Hertz (Hz) to 20 kilohertz (kHz). In contrast, bat echolocation calls generally range from 9 kHz to 200 kHz, with many insect-eating bats vocalizing between 20 kHz and 60 kHz. These sounds are classified as ultrasonic, making them inaudible to the human ear.
Some bat sounds can occasionally be heard by humans. These audible sounds are usually social calls, such as squeaks, chirps, or squawks, made during interactions within a roost or between mothers and their pups. Certain larger bat species or specific types of calls, like the clicks of spotted bats, may also fall within the human hearing range. Additionally, specialized equipment known as bat detectors can convert ultrasonic bat calls into frequencies that humans can hear, allowing researchers and enthusiasts to study bat activity.