WHAT ANIMAL IS THIS?

This animal lives in cold places like Antarctica. It is black and white. Its tail is short. It can walk. It can swim very well in the sea. It is a bird but it can’t fly. It has a black and orange beak. 

It eats seafood like fish. It slides on its belly on the snow. Some types of this animal are tall some of them are small. 

What animal is it?