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Penguin physiology
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 Adélie penguin with young (courtesy of Eric van Poppel and Caroline Don) |
Somebody described us as heavy-bodied, flightless birds with flipperlike wings for swimming. Now I want you, my dear reader, to look at us as well established creatures, whose adaptations to our uneasy world are marvellous.
To begin with, let us look at our "heavy body". I think you know that we have small tufts of down that grow beneath our feathers. They form a layer which traps air close to the skin. Of course, that is to prevent heat loss. Then we go deeper. Our skin is thick. Our fatty tissue layer provides not only a foodstore, but also plays an important role in insulation. Now I give you a minute to think of our large size and heat loss. Are you ready? It might surprise you that we have a problem with overheating, when on land. Yes, it can be a problem, but we are extremely good at solving it. We can pant or we can splay our webbed feet with water and let them act as cooling radiators. If it is too hot, we return to the water for a cooling dip.
I want you to know that we are not flightless: we fly under the water. We are wing propelled divers and we have the neural circuitry responsible for wing flapping, in spite of the fact that we cannot fly. Our high buoyancy (floating power) is due to air trapped between our feathers and in the air sacs of our respiratory system.
Our eyes are also wonderful. When we dive, our cornea loses its refractive power (its surface then separates media with near identical refractive index), but we are still able to see. We have a flat cornea with low refractive power in the air so that our eyes require less accomodation when we leave the water. The position of our eyes help us to maximize our field of vision under water. We see well enough to catch fish.
By the way, what about our food? It is salty! But we are not afraid to feed our chicks by regurgitation (i.e. bringing them food from our crop). We know that they can get rid of the salt with their salt glands and their kidneys (which can produce a concentrated urine).
References
M.N.O. Davies and P.R. Green: Perception and motor control in birds (Berlin,1994).
D.-N. Janes: Osmoregulation by Adelie penguin chicks on the Antarctic Peninsula (Auk 114:488-495, 1997).
G. Waller (ed): Sealife. A complete guide to the marine environment (1996).
More pictures from the Antarctic can be found at "A Wildlife and Landscape Image Archive".