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Physical CharacteristicsPectoral Flippers These are used to steer the dolphin through the water and to stroke one another. The stroking increases the bond between two dolphins. The fins are curved slightly and pointed at the tips. Flukes Dolphins use their flukes in an up and down motion to move through the water. Blowhole This is what the dolphins breath through. As the dolphin breathes, the air leaves the blowhole at speeds of over 100 mph. There are powerful muscles that are used to close the blowhole because if water got in it could drown the dolphin. Eyes The eyes produce a special slippery secretion which protects them from foriegn objects and water friction. Dolphins have acute vision both in and out of the water. A dolphin's eye is particularly adapted for seeing in water. Hearing Dolpins have a well-developed, acute sense of hearing. The auditory cortex of the brain is highly developed. The auditory nerve may have 67,900 or more cochlear fibers. This is twice as many as in the human auditory nerve. Hearing range. Bottlenose dolphins respond to tones within the frequency range of 1 to 150 kHz. (The average hearing range for humans is about .02 to 17 kHz.)(Ridgeway, 1990).
Sounds Dolphins and whales have voices, but it's a lot different from most other mammals. The limited visibility under water made sounds and hearing very important for them. The sounds of the whales are not produced with their mouth/beak but only inside their blow-hole. They also use frequencies that reach far beyond our hearing capabilities. Of course they can also hear these higher frequencies. Just as we, whales use sound to communicate. Large whales can communicate over very large distances (several hundred kilometers!) using very low frequencies. Dolphins usually use higher frequencies which limits the distance. Tooth whales use sound not only to communicate, but also to "see". Similar to bats they send out sounds and listen to the echo that comes back from objects (like fish or rocks). This kind of SONAR (SOund NAvigation Ranging) works very well. Even in complete darkness they can find their way through the ocean and also find their food. When you listen to the sounds you will usually hear two kinds of sounds. One that sounds like whistling (high pitched sounds) and one that sounds like a rattle or clicking. In general the whistles are for communication and the clicks is the SONAR. Sound reception. Most sound reception, or hearing, probably takes place through the lower jaw. Studies show that the lower jaw most effectively receives sounds with frequencies above 20 kHz (Brill, et al., 1988). A dolphin may also receive sound through soft tissue and bone surrounding the ear. Unlike humans, a dolphin's inner ear is encased in a separate bone, called the auditory bulla, which is connected to the skull with fibrous tissue. Thus, the bulla is essentially isolated from the skull, and sound enters the ear most efficiently through the jaw and middle ear. A fat-filled cavity in the lower jawbone appears to conduct sound waves through the jaw to bones in the middle ears. The lower jawbone of toothed whales broadens and is hollow at the base, where it hinges with the skull. Within this very thin, hollow bone is a fat deposit that extends back toward the auditory bulla (earbone complex). 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. (Brill, et al., 1988). The specialized anatomy of the dolphin ear probably allows it to localize sounds under water effectively, a task that is difficult for humans. A dolphin's middle ear cavity is filled with a highly vascularized (supplied with blood) tissue. When a dolphin dives, this tissue helps adjust pressure on the middle ear. A dolphin has small external ear openings, a few inches behind each eye. Each opening leads to a reduced ear canal and an eardrum. Some scientists believe that dolphins receive sound through these openings. Research has shown that the external ear openings may receive sounds with lower frequencies, below 20 kHz (Brill, et al., 1988). Other scientists believe that a dolphin's external ear openings are nonfunctional (Bryden and Harrison, 1986). Feeding. Often dolphins are very active during night time, for some this is their main feeding time. Their teeth are interlocking rows of conical pegs, suitable for holding slippery fish. They eat their fish whole, head first. In the wild an open mouth is a sign of aggression, as is head nodding. A sign of greater aggression is violent jaw clapping. Skin. The dolphin's skin is completely smooth allowing the dolphin to move easily through the water, and also reduce heat loss. Their skin may bear rake marks from other dolphins teeth during play or mating, and can easily become badly sunburnt if they strand. Their bodies are very streamlined so they may swim at high speeds through the water, and an example of this is their ears. Dolphin's ears are barely noticeable marked only by a small hole just behind the eye. In a bottlenose dolphin the ear is about 5-6 cms behind the eye and only 2-3 mm in diameter. Dolphins are able to dive to great depths, and also leap to great heights. They may leap to avoid predators or to show how powerful they are to females at mating time. Noisy splashing jumps may also be used to herd fish. To Sleep To sleep, a dolphin must shut down only half of its brain, as its breathing is under voluntary control. Dolphins take short cat-naps, floating just below the surface, then slowly rising to breathe. Please dont forget to sign my guestbook as I love getting mail.
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