Ultrasound refers to sound waves with frequencies beyond human hearing, typically above 20,000 hertz (Hz). While humans cannot perceive these high-frequency sounds, dolphins can both produce and interpret them. This specialized capability allows dolphins to interact with their underwater environment in ways not possible through vision alone. Their use of ultrasound is central to how they navigate, locate food, and potentially communicate within marine habitats.
Dolphin Sound Production
Dolphins generate high-frequency sounds, including ultrasound, through specialized structures within their nasal passages. Unlike humans and most mammals that produce sound using vocal cords, dolphins use “phonic lips” or dorsal bursa. These structures are located just beneath the blowhole in the nasal cavity.
When a dolphin produces sound, pressurized air is pushed past these phonic lips, causing surrounding tissues to vibrate rapidly. This vibration creates the clicks and other sounds dolphins emit. The sounds then travel forward through a fatty organ in the dolphin’s forehead called the “melon.” The melon acts like an acoustic lens, focusing the sound waves into a concentrated beam projected into the water.
Echolocation: Their Sonar System
Dolphins primarily utilize ultrasound through a biological sonar system known as echolocation. This process begins with the dolphin emitting high-frequency clicks, which travel through water. Sound travels approximately 4.5 to 5 times faster in water than in air, making it an effective medium for this sensory system.
These sound waves spread out and bounce off objects, returning to the dolphin as echoes. The dolphin receives these echoes primarily through specialized fat-filled cavities in its lower jaw. This fatty tissue conducts the sound vibrations to the inner ear, where the information is transmitted to the brain.
The dolphin’s brain processes these returning echoes, interpreting details such as the object’s distance, size, shape, speed, and even some aspects of its internal structure. This allows the dolphin to construct a detailed “sound picture” of its surroundings, much like a submarine uses sonar to map the seafloor. The time it takes for the sound to return helps determine the object’s distance, with longer return times indicating greater distances.
Applications of Dolphin Ultrasound
Dolphins apply their ultrasound capabilities to navigate and interact with their underwater environment. A primary application is navigation, especially in murky or dark waters where visibility is limited. By emitting clicks and interpreting echoes, dolphins avoid obstacles and find their way through environments.
Echolocation is also key to their hunting and foraging strategies. Dolphins use these high-frequency sounds to locate prey, assess their size and distance, and determine their movement. The precision of their echolocation allows them to detect details about fish, such as their thickness or whether they are moving away.
While echolocation clicks are distinct from communication whistles, ultrasound may also play a role in social interactions. Dolphins produce various sounds, including clicks and whistles, which serve different purposes. Although whistles are typically lower frequency signals for general communication, the high-frequency nature of echolocation clicks can contribute to their awareness of other dolphins’ locations and activities.