The penguin (Order: Sphenisciformes, Family: Spheniscidae) is an aquatic flightless bird.  They mostly live in the Southern Hemisphere.  However, only one species of penguin lives north of the equator.  They are able to swim in the sea with their two fin-like feathers.  They spend half of their lives on land and the rest in the sea.

The largest of the penguin species is the Emperor Penguin.  It grows to a height of about 1.1 meters and weighs 35 kilograms or a little more.  The little blue penguin or angel penguin is the smallest penguin species.  It is normally 35 cm to 40 cm tall and weighs about one kilogram.  Generally larger penguins are better able to absorb heat and can survive in colder climates.  Small penguin species are found in subtropical or subtropical climates.Penguins are well adapted for aquatic life.  Their feathers, which have been modified into fins, are useless for flight.  However, using them as flippers, penguins can swim surprisingly fast and light in the water.  They look like a bird flying while swimming.  So when penguins swim in water, you can see a series of bubbles behind them.  A layer of air beneath the feather helps preserve body heat from the cold Atlantic Ocean.  Penguins living in tropical and subtropical zones have relatively thin feathers.

All penguins have a white underside and a dark colored (mostly black) upper body.  It helps in camouflage.  Animals that can kill and eat penguins, such as the killer whale or the leopard otter, can be difficult to distinguish from the water`s surface when looking at the white-bellied penguin from the light splash.

Penguins swim at speeds of between six and 12 kilometers per hour.  It is also said that speeds up to 27 kmph have been observed.  Little penguins don't swim very deep.  They hold their food close to the surface of the water, and each swim lasts only a minute or two.  They can also swim as deep as necessary.  Great emperor penguins have been recorded to dive as deep as 267 meters and have been observed for 18 minutes.The behavior of penguins on land is unpredictable.  They walk on their feet, waddling on both sides, or slide on ice on their bellies.  However, penguins can actually outrun most humans or even them.  They slide over the belly to save energy and still move faster.  It is called tobogganing in English.

Their hearing is excellent.  The eyes are adapted for underwater vision.  These are penguins' primary means of catching food and escaping from other animals.  In air they cannot see very far.  Not much is known about their smelling power.