The word Penguin is thought by some to derive from the Welsh words pen (head) and gwyn (white), applied to the Great Auk which had white spots in front of its eyes (although its head was black); or from an island off Newfoundland known as Pengwyn, due to its having a large white rock. (In the latter case, the name may also have come from Breton.) This theory is supported by the fact that penguins look remarkably like Great Auks in general shape.
Part of Penguins adaptation to the cold snowy weather includes oily, unwettable feathers which cover the outer layers of penguins. Underneath is a layer of soft down feathers and under that a thick layer of fat. This keeps the penguins so warm they will actually fluff their feather to released trapped heat in order to cool down. In addition to their fine attire, penguins are well known for their swimming abilities. Using their flippers for propulsion and their feet as a rudder, penguins can swim in excess of 12 mph (20 kph). Through the use of air sacs to protect their lungs, penguins can stay under water for 15 to 20 minutes and dive as deep as 275 feet (900 meters). Penguins spend as much as 75% of their time underwater, searching for food in the ocean. When they are in the water, they dive and flap their wings. It looks just like they are flying! Penguins are shaped like a torpedo. Their body is built for the most efficient swimming with their average speed in the water being about 15 miles per hour.
Although very near-sighted on land, penguins posses exceptional vision in the water. Their eyes, like the many sea animals, are attuned to the colors of the sea--green, blue-green, and violet. They need this excellent vision to avoid leopard seals and killer whales, which are their primary predators in the ocean. On land their arch enemy are skuas (large birds) which snatch penguins chicks from nests. In the water, penguins typically feed on krill and fish. The dietary habits of penguins are relatively easy to monitor. Krill eating penguins excrete pink quano, while those eating fish leave behind white guano. The yolks of penguins eggs often are red denoting the consumption of krill. All penguins are countershaded for camouflage – that is, they have a white underside and a dark (mostly black) upperside. A predator looking up from below (such as an orca or a leopard seal) has difficulty distinguishing between a white penguin belly and the reflective water surface. The dark plumage on their backs camouflages them from above.