A. 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.
B. Sound production.
1. Toothed whales produce sounds for two overlapping functions: communicating and echolocating.
2. Beluga whales are extremely vocal. The frequency and large repertoire of their vocalizations earned them the nickname "sea canaries."
3. At least 11 different beluga vocals have been documented, including high-pitched, resonant whistles and squeals; clucks; mews; chirps; trills; and bell-like tones (Haley, 1978).
4. Beluga vocals can be heard above water (Nowak, 1991) and through the hulls of ships (Katona, Rough, and Richardson, 1983).
5. The larynx of toothed whales does not possess vocal cords.
6. Sounds are probably produced by movements of air between nasal sacs in the blowhole region. During sound production, a beluga whales's melon changes shape.
7. 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 (Sjare and Smith, 1986).
8. There is no evidence that beluga whales use anything resembling human language.
C. Non-vocal communication.
Besides vocalizations, belugas may communicate through facial expressions and physical contact (Ridgway and Harrison, 1981). Visual behaviors such as breaches, pectoral slaps (slapping a pectoral flipper on the water's surface), and lobtails are not as common in belugas as in some other whale species (Leatherwood and Reeves, 1983).
D. Echolocation.
1. 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.
a. Beluga whales produce directional clicks in rapid sequences called trains.
b. The click train passes through the melon. The melon acts as an acoustical lens
c. 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 (Au, et al, 1985).
d. Sound waves travel through water at a speed of about 1.6 km per second (1 mile/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.
e. The major areas of sound reception are the fat-filled cavities of the lower jaw bones. 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.
f. The brain receives the sound waves in the form of nerve impulses, which relay the messages of sound and enable the beluga whale to interpret the sound's meaning.
g. High frequency sounds don't travel far in water. Because of their longer wavelength and greater energy, low frequency sounds travel farther.
2. 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 (Katona, Rough, and Richardson, 1983).
3. 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-reflected echoes, which may aid them in navigating under an extensive ice pack (Smith, St. Aubin, and Geraci, 1990).
4. Many of the details of echolocation are not completely understood. Research on echolocation is ongoing.
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