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SENSES
17. Cetacean Sensations
Objective: To learn the differences between how whales and humans
perceive their environment.
Level: K-3, 4-7
Background:
Hearing
Whales have excellent hearing, which is helpful in the low light environment
of the ocean where vision is less dependable. Whales are thought to hear
very well at low-frequency ranges, but some whales may lack the ability
to hear higher frequency sounds. They have been observed to respond to
sounds such as cameras clicking underwater and boat-engine noise.
Baleen whales have a small external ear opening on each side of the head.
These openings lead to an auditory canal that is completely closed by
a waxy plug. It is not known how effective sound reception is through
this ear canal. Toothed whales do not have a waxy ear plug, and the ear
bones are not directly connected to the skull, as they are in baleen whales
and other mammals. The middle and inner ear follow the basic mammalian
structure. Surrounding the ear bones is a foamy liquid that contains air.
The air is responsible for stopping the sound waves travelling through
water and living tissues. This layer of air may acoustically isolate the
whale's ear, enabling the whale to detect which direction the sound is
coming from. In water, it is difficult to determine the direction of sound
if the ear bones are attached to the skull, because of the disturbing
vibrations coming from the skull.
Both toothed whales and baleen whales have the ability to emit sounds,
although toothed whales are more developed in this skill. Baleen whales
broadcast sounds widely, whereas toothed whales emit sounds in a directional
manner. Baleen whales emit primarily low frequency sounds, whereas toothed
whales emit a wide range of frequencies, from below 20 to 200,000 Hertz.
Humans have the ability to detect sounds in the range of 20-2000 Hertz.
Vision
The sun's light cannot penetrate very far below the ocean waves, especially
when it is blocked by abundant plankton near the surface. Like many fishes,
whales have adapted to seeing in the dim light. First, the eye of the
baleen whale is flatter than that of land mammals and the cornea is less
curved. This allows better vision in low-light conditions. But a whale
is nearsighted in air. A whale's eye also has a reflective layer behind
its retina, called the tapetum lucidum, which reflects light back
to the retina a second time. This takes advantage of the scarce light
at ocean depths. A cat also has this adaptation, and it is this tapetum
lucidum that causes the eye to reflect yellow when light is shined
on it. A whale's retinas contain mostly rods, cells that gather more low-intensity
light. Cone cells, which are responsible for colour vision, are much less
abundant. The Sperm Whale has very small eyes relative to its size, which
is associated with its feeding at great depths in the darkness of the
sea. Whales also have no tear ducts, as their eyes are constantly bathed
in water, but glands at the outer cornea and eyelids secrete an oily substance
that cleans and lubricates the eye.
Smell
During the foetal stage, baleen whales have olfactory nerves and bulbs,
but they are greatly reduced in the adult brain. Scientists have not yet
discovered whether these structures are functional. Toothed whales have
none, so they likely have no sense of smell.
Touch
Toothed whales have the sense of touch over the entire surface of the
body, but they are most sensitive around the head, flippers, belly and
genitals. A whale's skin is thin, sensitive and well supplied with nerves
and blood vessels. Whales do not have hair, but they do have vibrissae,
which are similar to the whiskers found on the upper lip of a domestic
cat. In whales, however, the vibrissae are much smaller and shorter than
those found on terrestrial mammals. In some species, vibrissae are present
as a juvenile, and then fall out; some are retained for life; and some
are present only in the embryo. Baleen whales have a well developed sense
of touch. Vibrissae are usually located at the end and sides of the lower
jaw and on the top of the head. They range from just a few to as many
as 250 (on the head of the Northern Right Whale). Baleen whales also have
dermal sensors that look like small lumps scattered over the head and
snout, as well as a few distributed over the body.
Taste
The sense of taste has not been well studied. Whales have taste buds on
their tongues, though not many, and those present have atrophied or degenerated.
It could be that whales have no need for refined tasting ability because
the constant flow of water through the mouth makes everything taste the
same, like briny water. It could also be that because whales eat basically
the same kinds of food, taste discrimination is not important.
Materials: blindfolds, objects for students to taste, touch, smell,
and listen to.
Procedure:
1) Divide the class into small groups, and ask the students to take turns
wearing the blindfold. Have each blindfolded student use one sense at
a time to identify various objects:
2) Taste - have one student feed the blindfolded student an unknown piece
of fruit. (check with students for allergies first).
3) Hearing - play a recorded sound, or blow up a balloon and have students
guess what made the sound.
4) Touch - present each blindfolded student with an unknown object, and
have them guess what it is by using only their hands.
5) Smell - have each student smell a well known scent, such as peppermint
or freshly cut grass, and have them guess what it is.
6) Once every student has had a turn to use his/her senses, put away the
blindfolds and discuss the activity. Which objects were the easiest/hardest
to guess? Which senses were the easiest/hardest to use? Why?
7) Using the background information above, make a list of differences
and similarities between whale senses and human senses. Discuss the reasons
for the differences.
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