Jonathan Martin, age 13, of Pine Ridge, So. Dakota, for his question:

What is the elephant bird?

From his name, one would expect him to come in the large economy jumbo size. And so he did. But he was not as big as the Arabian roc, reported by Marco Polo. This bird was said to fly off with elephants to feed to his chicks. Of course the impossible roc was a legendary bird. He was not related to the real elephant bird, except in people's imaginations.

So far as we know, the real elephant bird was the largest bird that ever lived on the planet Earth. The fact that he is extinct is no fault of modern man. Nobody knows why the last of his enormous kinfolk perished, for the tragedy occurred at the dawn of human history, perhaps 5,000 years ago.

In the distant past, several over sized birds developed on isolated islands where there were no predators to threaten them. The great moa birds of New Zealand were enormous. The bulky dodos and the ele¬phant birds had their heyday on the windswept island of Madagascar, in the mild Indian Ocean.

A couple of thousand years ago, seagoing peoples from various parts of Indonesia began arriving and several groups stayed to settle this island. But the last of the native elephant birds already had departed, or so we think.

We know that these giant birds existed from their fossil bones and from their enormous eggs, found in swampy bogs. The egg of the elephant bird really was jumbo sized. It was at least a foot long and weighed perhaps 18 pounds. The hollow shell held two gallons and had room enough for 30,000 eggs of the tiny bee hummingbird.

The chick that hatched from this jumbo egg was destined to stand ten feet tall. Nobody knows how long it took him to reach maturity, but finally he weighed 1,000 pounds. It's hard to imagine a bird weighing half a ton and standing ten feet tall. But on the island of Madagascar, some 5,000 years ago, there was such a bird.

Like the giant mopa of New Zealand, he resembled an oversized ostrich

with a bulky body, long neck and small head. His long, strong legs no doubt made him a fast sprinter, though so far as we know, there were no enemies around to chase him. Even if there had been, those mighty legs were powerful enough to bash a tiger to a pulp.

Judging from modern birds, there is a weight limit to flight. Our heaviest flying birds weigh about 14 pounds. Obviously, the elephant bird was grounded. However, his fossil breast bone is shaped like a ship's keel, which suggests that maybe his ancestors were flying birds    but no doubt very, very much smaller.

Marco Polo's fabulous roc makes a wonderful tale. But let's face it, such a bird was downright impossible. Just suppose the feathered monster was big enough to capture and dine on elephants.  A bird of such dimensions certainly would be unable to fly. And the fabulous roc was reported to zoom aloft on enormous wings, pounce down on an elephant and carry it back to his nest.