Watching penguins on TV or in a zoo can be a confusing experience. While they look like birds in a matter of appearance, penguins do not fly. But if you look up the definition of penguins, they are known as marine birds in zoological descriptions. You must have thought why are penguins birds? Indeed, the question becomes even more significant when you see penguins swimming in the water like fish or waddling on the Antarctic ice like two-legged animals.