Penguins==================================================
Penguins: the eyes have it!LIFE SCIENCES
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Myopic little men in tuxedos, or highly efficient
land/water animals? Recent research indicates
there’s more to penguins than meets the eye.
If you’ve every wondered what it would be like to
be able to see as clearly under water as you can on
land, just ask the nearest penguin.Most aquatic
animals are short-sighted on land. Most
terrestrial animals (and that includes us) are
far-sighted under water. But researchers have
discovered that penguins can apparently see equally
well in both environments, because of the unique
structure of their eyes.
Penguins have to be able to see well under water
because their diet consists mainly of plankton,
molluscs, crustaceans, and the inevitable fish.
Through a special slowing-down of their heart rate
they’re able, like many other diving animals, to
stay submerged long enough to search out and chase
whatever catches their fancy.
On dry land, it’s a different story-or has been up
to now. Waddling along on their flat little feet,
eyes fixed intently on the ground, penguins appear
myopic, inefficient and generally out of place.
In fact the reverse is true. During a recent stay
on the Falkland Islands, a Canadian researcher
discovered that penguins are able to recognize
individuals and navigate the rocky terrain on which
they live quite well. Long of body and short of
leg, they probably poke their heads forward as an
aid to balance. And as for looking at the ground,
they’re merely-like us-keeping an eye on where
they’re going.
The human eye is adapted for aerial vision, which
is why scuba divers-or even you and I in the local
swimming pool-must wear goggles or a face mask to
re-introduce air in front of our eyes in order to
see clearly.
Among vertebrates in general, the bird eye is
frequently described as the most efficient. Its
superior quality, combined with the fact that a
large number of birds-cormorants, pelicans,
seagulls, even ducks, as well as penguins-get their
food from water, obviously deserved research beyond
that possible in a controlled environment such as
an aquarium or zoo. Professor Jacob Sivak of the
University of Waterloo and his associate, Professor
Howard Howland of Cornell University, had a chance
to do that research recently. Their trip had but
one purpose-to study the structure of penguins’
eyes while observing their natural habitat.
The Falkland Islands, off the coast of Argentina,
offered this opportunity, being one the few areas
outside Antarctica where penguins can be found in
large numbers. Three of the 16 known species were
located there: the Gentoo, which live on flat
areas right off the beach; the Magellan (also
called Jackass), which live in burrows; and the
Rock-hoppers, which live among the rocks along the
cliffs.
The Rock-hoppers were by far the most common,
having a population of well over 100,000. The
general rule is, the smaller the penguin, the
meaner the temperament, and the researchers did
witness the odd fight. Their flippers may look
pretty useless out of water, but it’s not smart to
play around with a penguin. Hel’ll stand his
ground in a face-off and if you’re foolish enough
to get too close, those flippers can knock you
flat.
Dr. Sivak and his associate, however, had little
trouble. Rock-hoppers always congregate in fairly
tight groups, as a defense against predatory birds
such as the skua (a large seagull that thinks it’s
a hawk), and two more upright figures in their
midst didn’t seem to bother them.
Standing as close to their subjects as 0.3m, the
scientists used two devices: one, developed by
Professor Howland, to take photographs of the
penguins’ eyes; the othger, developed by Dr. Sivak,
to shine a series of concentric circles on the
cornea and give a measurement of how reflections of
objects are altered by curvature of the eye.
Despite the fact all the work had to be done at
night-the only time the penguins’ pupils were
dilated enough-the results were worth it.
Comparison of the photographs with similar photos
of human eyes, and study of the internal structure
of the eyes of creatures discovered killed by seal
lions, proved the scientists’ theory that the
penguin’s eyes are the secret of its survival.
In general terms, a penguin eye and a human eye are
almost identical. Both have the same components
necessary for vision-a cornea through which light
can enter; an iris which controls the amount of
light that enters; and a crystalline lens that
focuses the light onto the back of the eye where a
specialized membrane, the retina, receives it and
passes the message along the optic nerve to the
brain for interpretation.
In the penguin eye, hoever, there are many subtle
differences. The cornea, for example, is markedly
flattened compared to ours — so much so that it
almost resembles a window-pane. This greatly
alters the angle at which light can enter the eye
and is very important for underwater swimming, when
light enters the eye obliquely through a medium
(water) whose density is quite different to the
density of air.
The penguin iris is controlled by a very powerful
muscle which is able to drastically alter the shape
of the lens attached to it, depending on whether
the penguin is in or out of the water. The lens,
comparatively larger than ours and differently
shaped, focuses the light coming through the
flattened cornea onto the retinal body at the back
of the eye. In this way, the penguin eye adapts to
whatever medium it happens to be in at the time.
Interestingly, there was no evidence of eye
problems (apart from one incident of blindness due
to injury) in the group of penguins studied. Of
course penguins don’t read, watch TV or encounter
any of the numerous irritants we land-bound animals
subject ourselves-or are subjected-to during our
lifetime.
Both the testing devices and methods used in this
study are easily adaptable for use with human eyes,
paving the way for fast, easy identification of eye
problems. Also, the researchers hope that the
insights they’ve gained into how animals deal with
two environments may lead to knowledge of how humans,
in the future, might do likewise.
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PENGUINS (C) 1987 Ontario Science Centre.
May be duplicated for use on other information
services with permission.
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