William Audrey, Age 11, Of Charlotte, N.C., for his question:

Do all birds fly?

At some time in the past, the ancestors of all our birds may have been able to fly. But some of them have long since lost the power of flight. The huge ostrich, for example, has been grounded for countless generations. Though he has fine, feathery wings, they are not big or strong enough to lift his bulky body into the air.

The penguin is a water bird who is not at all interested in flying. But he does need his wings to swim and dive through the sea. The wings of the penguin are shaped like flippers, and he could never use them for flying. These and other non flying birds may have become grounded because for generations they did not use their wings for flight.