kinds of birds wear feathers, except some when they are very little in
the nest."

"Quite right, little girl," said the Doctor. "Every bird has feathers,
and no other animal has feathers. So we say, 'A bird is known by its
feathers.' But what do you suppose its feathers are for?"

"To make it look nice and pretty," said Dodo promptly.

"To make it lighter, so's it can fly," added Nat.

"To keep it warm, too, I guess," was Rap's answer.

"Well, you are all three partly, but not quite, right. Certainly the
beauty of a bird depends most on its feathers, being not even skin-deep,
as you may well believe, if you ever noticed a chicken Mammy Bun had
plucked. But, Nat, how can feathers make a bird lighter, when every one
of them weighs something, and a bird has to carry them all? They make a
bird a little heavier than it would be without them. Yet it is quite
true that no bird could fly if you clipped its wings. So some of its
feathers enable it to fly--the large ones, that grow on the wings. Then,
too, the large ones that make the tail help the bird to fly, by acting
like a rudder to steer with. Perhaps the small ones too, all over the
body, are of some help in flight, because they make a bird smooth, so
that it can cut through the air more easily--you know they all lie one
way, pointing backward from their roots to their tips. Then when Rap
said feathers keep a bird warm, he guessed right. Birds wear plumage as
you do clothes, and for the same purpose--to look nice and keep warm."

"But what is 'plumage,' Uncle Roy?" asked Dodo; "I thought you were