Birds may be best identified for their ability to fly, but not all species have that advantage. Several birds -- from New Zealand's kiwi to the great African ostrich -- have evolved wings or grown to a size which prevent them from taking flight. Where they cannot get airborn, like other birds, they have adapted other important skills: some can run much faster than flying birds, and others have become impressive swimmers. Whatever the reason for their evolution, none of them seems to mind being stuck on the ground.