Aquatic flyers

Penguins have for all intents and purposes learned to fly in water, which is a fluid with a density about 8,000 times greater than air. Therefore, although they have pectoral muscles as large as those of a bird capable of flying in the air, these muscles act on two wings that are so small that they are completely useless for soaring through the air.

What is the evolutionary principle that led them to this adaptation? Finding food more easily than other birds. Many birds in fact have adapted to catch their food below the surface of the water. Some of these are great flyers, such as gulls, albatrosses and pelicans; they have long wings, adapted for flight in the atmosphere, but are completely or nearly unable to swim underwater. If the prey manages to dive even 50 cm, it is safe.

Other birds have learned to swim and have become, in a sense, amphibians: cormorants, guillemots, sea magpies: these birds fly using their wings and swim with their legs. They therefore need two sets of powerful muscles, one to fly and one to swim.