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Penguins
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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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ADDITIONAL FEATURED ESSAYS
Endangered Species 3
All over the world there are species of animals and plants that are said to be "endangered". By calling them endangered,
Australia
Although only a dozen plant families are unique to , there are 530 unique genera and many unique species within these ge
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