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Senses
A. Hearing.
1. Killer whales have an acute sense of hearing, and the auditory cortex of the brain is well developed.
B. Hearing range.
1. The average hearing range for humans is about 0.02 to 17 kHz, but killer whales have responded to tones within the frequency range of about 0.5 to 125 kHz.
2. Peak sensitivity for killer whales is about 20 kHz. Sensitivity declines gradually above and below 20 kHz.
C. Sound reception.
1. Most sound reception, or hearing, probably takes place through the lower jaw. A killer whale may also receive sound through soft tissue and bone surrounding the ear. High frequency sounds in the range of 50 kHz and above appear to be received effectively by the lower jaw.
The fat filled lower jawbone conducts sound waves through the jaw to bones in the middle ears.
2. The fat-filled lower jawbone conducts 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.
3. Odontocetes can produce sounds for two overlapping functions: communicating and navigating. A killer whale can communicate and navigate at the same time. Higher frequency clicks probably function primarily in echolocation, but the function of lower frequency pulses created by killer whales is unknown.
D. Echolocation.1. The term echolocation refers to an ability that odontocetes (and a few other animals like bats) possess that enables them to locate and discriminate objects by projecting high-frequency sound waves and listening for echoes. Odontocetes echolocate by producing clicking sounds and then receiving and interpreting the resulting echo.
2. Killer whales produce directional, broad band clicks in trains. Each click lasts less than one millisecond.
a. Clicks include a wide range of frequencies, with most energy in the range of 10 to 80 kHz. A 25-kHz peak is common, but individuals can probably vary the peak frequency to suit the circumstances.
b. The click train passes through the melon (the rounded region of a killer whale's forehead), which contains lipids (fats). The melon acts as an acoustical lens to focus these sound waves into a beam, which is projected forward into water in front of the whale.
c. High frequency sounds do not travel far in water. Because of their longer wavelength and greater energy, low frequency sounds travel farther.
3. Sound waves travel through water at a speed of about 1.5 km/sec (0.9 mi/sec), which is four-and-a-half times as fast as sound traveling through air. The sound waves produced by a killer whale bounce off objects in the water and return to the killer whale in the form of an echo.
4. Many of the details of echolocation are not completely understood, so research in this field continues. However, studies conducted thus far have shown that echolocation allows odontocetes to determine size, shape, speed, distance, direction, and even some of the internal structure of objects in the water.
E. Eyesight.1. Killer whales have acute vision both in and out of the water.
2. A killer whale's eyes are on each side of the head, located just behind and above the mouth, and in front of the white eyespot. The ears, located just behind the eyes, are small inconspicuous openings, with no external flaps or pinnae.
3. Glands at the inner corners of the eye sockets secrete an oily, jelly-like mucus that lubricates the eyes, washes away debris, and probably helps streamline the eyes as a killer whale swims. The tear-like film may also protect the eyes from infectious organisms.
4. The eye and external ear openings of killer whales are well camouflaged and located near the white 'false eyespot'. These false eyespots may protect a killer whale's eyes from prey they are attacking. Prey animals may attempt to injure the eyes of a predator in order to escape, but the obvious false eyespots may draw attention away from the killer whales' real eyes.
5. To see above the water, killer whales lift their heads above the water's surface. This behavior is known as spy-hopping.
6. In studies at SeaWorld, killer whales visually discriminated among similar objects. During more than one hundred trials a killer whale was shown an object and cued to find a matching object. When given two choices, the whale chose the matching object with 92% accuracy, and when three choices were presented the whale's accuracy was about 82%. Researchers did not determine whether the whale was responding to shape, size, or color. Future studies may provide more detailed information on the visual abilities of killer whale.
7. In the often darkened waters of the ocean, eyesight may be of little help in locating prey. Under these conditions, killer whales probably rely on sound production and reception to navigate and find prey in murky waters.
Anatomical studies and observations of behavior indicate that a killer whale's sense of touch is well developed. A killer whale's skin appears to be sensitive to a broad range of tactile sensations.
G. Taste.Little is known about a killer whale's sense of taste. They do have taste buds, although they haven't been well studied. In zoological parks, killer whales show strong preferences for specific food fishes.
H. Smell.The olfactory (smell) lobes of the brain and olfactory nerves are absent in all toothed whales, indicating a lack of smell. Being air-breathing mammals that spends a majority of time under water, a sense of smell would go largely unused in killer whales.
