Scott Richmond, age l2, of Cl arkdale, Ariz for his question:
Why does a duck have holes in his bones?
When you have duck for dinner, you almost certainly find a bone. You might expect it to be hard and solid all the way through. But this is not so. It is easy to break a sizable wing bone or thigh bone into brittle splinters. Then you discover that the inside of the bone is filled with holes. In fact, it is almost hollow. There are also holes is chicken bones, turkey bones and in all bird bones,
This is because the most important thing in the bird world is flight. True, the farmyard duck does not fly very much. But his wild cousins fly thousands of miles every year. The fat turkey does not fly. But his ancestors did. Even the ancestors of the 300 pound ostrich took to the air. And the body of every bird was originally designed for flight,
His children may give up flying and, like the lily white duck and the ostrich they may grow too heavy for flight. But the features which made it possible for them to fly still remain. Their arms or front limbs are wings. They are covered with feathers. They have special air sacs in their bodies and light.‑weight bones with more air pockets to make them buoyant.
It took perhaps 50 million years for these special features to develop. Gradually, the birds were set apart from the reptile ancestors from which they sprang.
When changes of this kind are made in the world of nature, they can never be undone. The wings developed for flight cannot be traded back for an extra pair of legs when a bird decides to live forever on the ground. His feathers developed from the scales of his ancestors and he can never have those scales back again. He may‑ get fat and heavy.
But he will never lose the air sacs in his body or the hollow bones which developed so that he could launch his light‑weight body into the air.
This rule holds true throughout all of nature. The ancestors of the cow developed a. complicated stomach for safety in the wilds. They could grab a meal, swallow it whole and chew it later in some safe hiding place. The cow no longer needs to hide, but she still has the complicated stomach which was developed to make the life of her ancestors safe.
When he flies, a bird mounts up on steps of air. His flapping wings scoop up cushions of air below him. Watching him,, it looks easy. But it took millions of years for birds to develop flying bodies. They are smooth and streamlined to reduce air resistance. But most important, they are very light. For no bird weighing more than 30 pounds can take to the air.
Feathers are light and filled with tiny air pockets which make. them warm. A flying bird keeps his silky plumage smooth and streamlined. His legs and feet are light and slender. The heaviest part of his body are the strong flying muscles of his breast. But even this is made light and . buoyant by the air sacs and pockets in his body and slender bones. These spaces connect with his lungs and when he flies he takes a deep breath and fills them full.