Even the little wren has some
weight; much more the crows which make their nests in the topmost branches
of the trees. We say "as light as a feather"; yet the downiest feather has
some weight, and will find its way to the ground if not kept up by wind or
breath.
It is true that the "feathered fowl," as all kinds of birds are called
in the Bible, are very much heavier than the air in which they float and
swim, using their wings for oars, just as the fish use their fins. But
do you remember that little balloon inside the fish, which enables it to
rise through the water? A bird is almost a live balloon; as it flies, it
breathes air into every part of its body; this air becomes heated, and is
kept warm by the feathers; and as hot air becomes light, the bird is so
much lighter than the air which surrounds it, that it can easily rise
higher and higher, until, like the skylark, its little quivering body seems
almost lost in the far blue sky, and its "waterfall of song" alone shows
where it is.
[Illustration: "THE WHITE SEA-GULL, THE BOLD SEA-GULL, A JOYFUL BIRD IS
HE."]
The bones of a bird are very strong, but they are also very light; if you
look at the bones of a chicken, you will see that some of them are hollow;
when the bird was alive, those hollow places were all filled with air. Take
a dead bird and look at the quills at the roots of the feathers; and now
watch that swallow as it darts so rapidly hither and thither.
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