Penguins are seabirds that cannot fly. There are 18 species of penguins in the world. Their size and weight vary significantly but all have similar structure and feathers. The smallest is the Little Blue Penguin of 30 cm, 1.2 kg and the largest is the Emperor Penguin of 80 - 100 cm, 15-40 kg.
They have three thick layers of short, dense and oily feathers forming a waterproof coat. Penguins in the warmer region have a thinner feathers and fat layer than the cold polar ones. The thick coat of fat layer protects them from the cold so that they can stay in the icy sea for long periods of time.
Penguins have highly streamlined bodies. The wings are reduced to strong, narrow and hard flippers. They can move very fast under water. Their legs and the strong tail are like rudders to steer them along.
They are less active on land. They almost always stand upright and use the strong and thick tail feathers as a support. They waddle rather than walk because of their short legs, but on ice they can move fast.
Penguins live together and breed in groups. They lay one or two eggs but usually only one chick is reared. Penguins eat small fish, crabs and squids. Most of them eat snow and all of them drink salt water and fresh water. They can live long periods without food on land.