Richard McCall, age 8, of Florence, South Carolina, for his question:

Is it true that some birds cannot fly?

The birds are the winged wonders of the world. The mighty eagle teaches the moun¬tain crest, the graceful gull soars for hours above the sea. Some birds fly better than others    but we expect them all at least to try. However, a few birds gave up trying long ago and they cannot fly at all.

The biggest bird living in the world is the ostrich. If you straddle on your daddy's shoulders, you are tall enough to look this big bird in the eye. On the scales, he weighs as such as a big man and a boy. Yet this whopping bird cannot fly as well as a small sparrow    in fact, he cannot fly at all. He has wings adorned with feathery finery, but they could not lift him off the ground even if a lion were chasing him. What's more, the ostrich is not the only flightless bird. The rhea bird also is grounded. So are the emu and the cassowary. The stringy little kiwi is a flightless bird and so are all the neatly dressed penguins.

There were many different birds ages ago and over the generations they kept changing. Once upon a time all of the different birds could fly, but for one reason or another, a few types gave it up. Their wings got no exercise so they grew weak. After many generations, these birds lost the power to fly and had to stay forever on the ground. This, of course, was sad. But several other things happened to help the flightless birds and to make their lives bearable. In fact, most of them live rol¬licking lives and they do not envy their flying cousins at all.

Maybe most flightless birds were fatties who loved to over eat. In any case, their descendants became heavy whoppers. And nature has a rule that limits the weight of a flying bird to 35 pounds. The African ostriches and the Australian emus, the South American rheas and the cassowaries of New Guinea are too heavy to pass the 35 pound flying test. The whiskery, chicken sized kiwi of New Zealand weighs only four pounds. But his stubby little wings, hidden under his shaggy coat of hairy feathers, are too puny to lift him off the ground. A flying bird has mighty wing muscles fixed to a breastbone shaped like the curved keel of a ship. Most non flying birds have flat, raft shaped breastbones and their mightiest muscles are in their legs. The word "ratite" means raft and experts call these non flyers ratite birds.

The penguins, so neatly dressed in tuxedos, are flightless birds of a different type. They have keel shaped breastbones like the flying birds and many of them are small enough to pass the flying test. But penguins lack the stiff quill feathers needed for flying. And their short, stubby wings are not suitable for air flight. In the seas where they fish and frolic, they use them as flippers for flying under the water. No penguin would trade his stubby flippers for the wings of an eagle.

Ostriches and other big ratitls do not yearn to fly because they enjoy their way of life on the ground. Being heavy suits them because most of their extra weight is in the muscles of their mighty legs. The fierce cassowary can kick and claw and peck his worst enemy to death. Tall Mr. Ostrich can see his enemy coming from afar and take off for safety at a steady 35 miles an hour.