Llynda McFarland, age 9, of Lancaster, Pa., for her question:

What do they call birds that cannot fly?

A flying bird has a breast bone shaped like the tapered keel of a ship. This shape is necessary to hold the strong muscles needed to lift him above the ground. Some birds do not fly because their breast bones are the wrong shape. The non flying ostrich has a flat breast bone shaped like a raft. It could not hold the strong muscles needed for flying.

The ostrich is called a ratite bird, the word ratite coming from an older word for raft. The emu and the rhea, the kiwi and the cassowary also are ratite birds, and none of these can fly because they have flat, raft shaped breast bones.