We are interested in a class of animals with backbones known as birds. Birds have feathers and lay eggs. All birds have wings. However, not all birds can fly. The Ostrich is too heavy to fly.
Penguins use their wings to swim, instead of to fly.
After many centuries, their ancestors had evolved to the point where they were unable to fly. Often these birds live on remote islands in the Pacific Ocean. They are vulnerable to introduced animals and snakes. There is a surprising amount of debate about some birds. They may actually be a race of a similar species in the same genus.