Flightless birds have a flat breastbone or a greatly reduced keel. Flightlessness is an adaptation that usually evolves on islands where predators are absent. However, not all flightless birds are found on islands. Ostriches live on the African savannas . Since ostriches can't fly away to escape predators, ostriches have evolved another defense.
Ostriches can use the claws on their feet as dangerous weapons when threatened.