The production of a rapid, short burst of sound, commonly described as a click, is a widespread biological phenomenon found in numerous animal species. This acoustic signal is an effective tool for transmitting information, especially where visual cues are limited, such as in deep water or at night. The function of these sounds is diverse, ranging from navigating the environment to signaling a warning or aiding in predation.
Clicking for Navigation and Hunting
Many marine mammals rely on producing clicks as a form of biosonar, known as echolocation, to perceive their dark, underwater world. Toothed whales, or odontocetes, emit directional pulses of sound and interpret the returning echoes to locate objects and track prey. The density and speed of sound in water make it an ideal medium for this long-distance acoustic mapping.
The sperm whale, which holds the record for the loudest click in the animal kingdom, uses these sounds for deep-sea hunting. These powerful clicks serve as long-range sonar, allowing the whale to detect prey like deep-dwelling squid over a mile away. As the whale closes in on its target, the clicks rapidly increase in frequency, transitioning into a high-repetition rate “creak” or “buzz” that provides detailed information for the final moments of the pursuit.
Dolphins and porpoises also use echolocation, but with a different acoustic specialization. Species like the harbor porpoise utilize narrow-band, high-frequency (NBHF) clicks, typically centered around 130 kilohertz. This high frequency allows for a narrow sound beam and high spatial resolution, which is advantageous for scanning for small prey and navigating cluttered coastal waters. The rate of these clicks shortens dramatically as the animal approaches an object, allowing for precise, instantaneous spatial updates.
Terrestrial Clicks for Warning and Signaling
On land and in the air, clicking sounds serve a variety of short-range purposes unrelated to navigation, often involving defense or social communication. The most recognized example is the click beetle, which uses its sound-producing mechanism primarily for locomotion and self-defense. When overturned, this beetle snaps a specialized spine against a ridge in its exoskeleton, generating an audible click that simultaneously launches it into the air.
This sudden movement and loud sound, often called a startle display, can momentarily disorient or deter a predator, giving the beetle a chance to escape. Certain species of geckos, which are one of the few vocal lizard groups, produce clicks and chirps as a form of social communication. They use these sounds to define territory, warn off rivals, or attract mates, often by rapidly snapping their tongues against the roof of their mouth.
Other terrestrial species employ clicking for social signaling within their groups. Some primates, such as the Barbary macaque, use a rapid “teeth chattering” sound to communicate social intentions. This acoustic signal can function as a sign of submission or appeasement to reduce tension during social interactions, or it can be used for affiliation to reinforce bonds.
Specialized Anatomical Mechanisms for Sound
The physical generation of clicking sounds across different animal groups involves three primary anatomical strategies. In toothed whales, the sound is produced not by the larynx but by a pair of soft tissues called phonic lips, or “monkey lips,” located just below the blowhole. Air is forced past these lips, causing them to vibrate and produce the acoustic pulse.
This sound is then channeled and focused by the melon, a large, fatty organ in the whale’s forehead that acts as an acoustic lens, directing the click into a focused beam. The skulls of toothed whales are also notably asymmetrical, a feature linked to the complex process of directing and receiving the echolocation clicks.
In many invertebrates, the clicking mechanism involves a mechanical action known as stridulation, where a scraper is rubbed against a file. Many insects, such as crickets and certain beetles, utilize this method by moving a specialized body part with a series of fine ridges (the file) against a hardened edge (the scraper) on another part of the body. The rapid friction between these two surfaces creates the characteristic clicking or chirping sound.
The click beetle, for instance, uses a skeletal mechanism where a prosternal spine on the underside of its body is locked into a notch on the mesosternum, storing elastic energy. When muscles rapidly release the spine from the notch, the sudden impact of the spine against the exoskeleton produces the loud click and the accompanying catapulting motion.