Why Sound in the Sea is Important
Beluga whales probably rely on sound production and reception to navigate, communicate, locate breathing holes, and hunt in dark or murky waters. Under these conditions, sight is of little use.
Sound Production
Toothed whales produce sounds for two overlapping functions: communicating and echolocating.
Beluga whales are extremely vocal. The frequency and large repertoire of their vocalizations earned them the nickname "sea canaries".
Vocalizations
- At least 11 different beluga vocals have been documented, including high-pitched, resonant whistles and squeals; clucks; mews; chirps; trills; and bell-like tones.
- Beluga vocals can be heard above water and through the hulls of ships.
The larynx of toothed whales does not possess vocal cords
Sounds are probably produced by movements of air between nasal sacs in the blowhole region. During sound production, a beluga whale's melon changes shape.
Scientific evidence suggests a general association between behavioral activity and the various types of vocals beluga whales use. For example, researchers have observed that beluga whales tend to emit more squawk-type calls during periods of social interaction than during alarm situations.
There is no evidence that beluga whales, or any other whales, use anything resembling human language.
Non-Vocal Communication
Besides vocalizations, belugas may communicate through facial expressions and physical contact. Visual behaviors such as breaches, pectoral slaps (slapping a pectoral flipper on the water's surface), and lobtails (slapping flukes on the water's surface) are not as common in belugas as in some other whale species.
Echolocation
The term echolocation refers to an ability that toothed whales (and some other marine mammals and most bats) possess that enables them to locate and discriminate objects by listening for echoes.
Toothed whales echolocate by producing clicking sounds and then receiving and interpreting the resulting echo.
Sound waves travel through water at a speed of about 1.6 km per second (1mile/second), which is four and a half times as fast as sound traveling through air. The sound waves produced by a beluga whale bounce off objects in the water and return to the beluga in the form of an echo. In one echolocation study, a single beluga produced signals with peak frequencies of 40 to 60 kHz in San Diego Bay, California, and 100 to 120 kHz when moved to Kaneohe Bay, Hawaii. The different frequencies were thought to be a response to the amount of ambient noise in the area.
Beluga whales produce directional clicks in rapid sequences called trains.
The click train passes through the melon. The melon acts as an acoustical lens to focus these sound waves into a beam, which is projected forward into the water in front of the whale.
The major areas of sound reception are the fat-filled cavities of the lower jawbones. Sounds are received and conducted through the lower jaw to the middle ear, inner ear, and then to hearing centers in the brain via the auditory nerve.
By this complex system of echolocation, toothed whales can determine size, shape, speed, distance, and even some of the internal structure of objects in the water. For belugas, echolocation is especially important for navigating under ice fields and locating breathing holes in the ice.
Studies show that beluga whales have a higher capability of echolocating in the presence of ambient noise than bottlenose dolphins.
Belugas are also able to receive and use surface-reflective echoes, which may aid them in navigating under an extensive ice pack.
Many of the details of echolocation are not completely understood. Research on echolocation is ongoing.
Loud Impulse Sounds
Loud impulse sounds recorded from bottlenose dolphins may serve to stun prey or confuse predators; however this suggestion has not yet been confirmed.
Other Sounds
Dolphins produce sounds above the water surface. Dolphins also make sounds when they jump, breach, or strike the water surface with flippers and flukes. These sounds may function in communication.
