Penguins are a type of bird, but unlike most birds they cannot fly. There are over a dozen species of penguins that live in the southern hemisphere, and they are especially prominent in Antarctica. They are part of the order Sphenisciformes and the family Spheniscidae.
The body of a penguin enables it to withstand the harsh conditions of its environment. There is a heavy layer of fat under the creature's skin, and above the skin is a layer of down for added warmth. Despite living in freezing temperatures, the penguin's body heating system works so well that sometimes the creature has to ruffle its feathers to cool off. The bird's outer feathers are covered with oil which, in addition to the creature's torpedo shaped body, enables it to move effectively through water for long periods of time.
Penguins go back and forth between land and the water. They take to the water to pursue fish, squid, krill and other food items. Penguins drink salt water, and their bodies separate the water from the salt to provide fresh water. Penguins return to land to lay eggs and tend to them. With many species, both the male and the female take turns keeping the eggs warm and safe.