Gina Cohn, age 11, of .Schenectady, New York, for her question:

What is the highest that birds can fly?

When a human pilot plans a trip, he checks his flight plans with the Federal Aviation Authority. But the birds do no such thing. They do not inform us where they are heading or report where they have been. This is natural and understandable. But it does make it difficult for scientists to trace migratory paths and other fascinating achievements of the bird world. It is especially difficult to verify how high they can fly when they try. Nevertheless, human bird lovers keep trying.

Birds, of course, need to breathe oxygen. Until recently, most scientists assumed that they could not fly up there where the air is too thin for people to breathe. For example, when people climb Mount Everest they take tanks of oxygen. At 16,000 feet, the air is so thin that mountaineers begin to puff and walking and talking requires tremendous effort. As they climb higher, they must draw on their oxygen supplies to keep going. Migratory flights require tremendous energy and surely no bird can fly at heights of more than three miles, where human beings gasp for breath. At least, this is what experts assumed.

Then a year or so ago, a naturalist was mountaineering in the world's highest mountains, the mighty Himalayas of Asia. One night he rested 16,000 feet above sea level and gazed at the serene splendor of the enormous peaks around him. Over there, 27,824 feet above sea level, the snowy peak of Makalu seemed to touch the starry sky. Then into this lofty silence came a soft hum from afar. It grew louder and nearer    clear enough for the astonished observer to recognize it. Without a doubt, ft was the sound of flying geese    great birds migrating over the peaks of the high Himalayas.

No, they did not chart their flight over the low peaks of 14,000 or 16,000 feet. They headed straight for Makalu and topped the snowcapped summit, more than four miles above sea level. Were they exhausted? Not at all. The great birds had enough energy to keep up their honking and tooting conversations all the way.

One might suppose that this set the record in how high birds can fly. Not at all. Later the excited observer reported his discovery to other mountaineers in this lofty region. They were not impressed    because many of them had seen these migrating

What is the highest that birds   for Friday, May 28, 1971 geese fly over the summit of Mount Everest itself. This highest peak is 29,028 feet above sea level. In fact, many who know the region are used to watching these geese cross the lofty peak twice each year. It seems that they migrate between India and Tibet, and flying at heights of six miles or so is a regular occurrence.

So far as we know, this is the highest that birds fly. Maybe they could fly even higher if the earth had higher mountains to cross. At present, the astonished scientists are unable to explain how these lofty flights in the thin air are possible. Meantime, the splendid geese continue their impossible flights    and have enough cheerful pep to keep up their booming conversations.