Dolphins navigate and perceive their environment primarily through sound. Since sight is limited in the murky underwater habitat, they rely on a sophisticated biological sonar system. This system helps them detect objects and locate prey with remarkable precision. The central mechanism involves the emission and interpretation of high-frequency sound waves.
The Use of Ultrasonic Clicks
Dolphins use ultrasound for echolocation, also known as biosonar. Ultrasound refers to sound waves with frequencies above the range of human hearing, typically exceeding 20 kilohertz (kHz). For echolocation, dolphins produce short, rapid, high-frequency sounds known as “clicks.”
These clicks, which can reach up to 150 kHz, are distinct from the lower-frequency whistles used for communication. The shorter wavelengths of ultrasound clicks provide finer detail necessary for resolving the size and shape of targets. Dolphins adjust the frequency of their clicks, using lower frequencies for searching long distances and switching to higher, more rapid clicks when approaching a target.
Anatomy of Sound Production
The generation of ultrasonic clicks occurs within the dolphin’s nasal passages, not the larynx. Sound vibrations originate at structures known as the phonic lips, located just beneath the blowhole. The sound is created when pressurized air is forced past the phonic lips, causing the connective tissue to vibrate. The air used to create the sound is recycled internally, preventing air from escaping the blowhole.
This internal air movement is controlled by surrounding nasal sacs that regulate the pneumatic pressure driving the phonic lips. Once generated, the clicks travel forward and are focused into a narrow, directional beam by the melon. The melon is a globular, fatty structure in the dolphin’s forehead that acts like an acoustic lens. It is composed of specialized lipids that refract and concentrate the sound waves before projection into the water.
Interpreting the Acoustic Environment
Echolocation relies on sending out a sound pulse and receiving the echo that returns after bouncing off an object. The time it takes for the echo to return provides the dolphin with information about the object’s distance. Returning echoes are primarily received through a specialized, acoustically sensitive fat-filled channel in the lower jaw. This fat body serves as the main pathway for transmitting high-frequency signals to the middle and inner ear.
The dolphin’s brain processes subtle variations in the returning echoes to extract information about the target. By analyzing the echoes, a dolphin can determine the object’s size, shape, speed, and direction of travel. They can also discern the internal density and structure of an object, allowing them to distinguish between materials or detect the air-filled swim bladder inside a fish.
This sensory ability is used for foraging, navigating complex environments, and avoiding predators. When hunting, dolphins increase their click rate dramatically as they close in on a target, a rapid sequence known as a “terminal buzz.”