December fall, the procession
flutters back south again, one by one or in great flocks, dropping away
like falling leaves in the forest, and the birds that we see later are
likely to be Citizens.

"The early Robin may have a second brood and the Hummingbird eggs in her
nest, before the Marsh Wrens have even been seen.

"In the Southern States the birds arrive and build sooner than in the
Northern. A cold spring may delay the on-coming migration, or a warm
autumn retard the return movement. But as you study birds you will soon
see that each one has his own place in the procession, and usually keeps
it. Year by year this vast procession goes on in the air, back and
forth, night and day, like the ceaseless ebb and flow of the tides at
sea. Bird-waves flow on forever, in their appointed times, and none of
Nature's aspects are more regular or more unfailing. It almost seems,
boys, as if birds made the seasons--as if winter in the Middle and
Northern States might be called the 'songless season.'"

CHAPTER VII

THE BIRD'S NEST

"I wonder why some birds build their nests so very early, when it is
cold, and there are no leaves on the trees, while others wait until it
is almost summer," said Rap, as they walked down a narrow lane toward
the river. There were bushes lining the path on each side, and from the
singing you would think that every bush had a bird on each twig. In
fact, there were so many birds in sight that Nat did not know which to
ask about first, and so kept looking instead of talking.

"The birds who are Citizens are usually the first to build," answered
the Doctor. "They merely roved about during the winter months, and had
no long journey to make before they reached the home trees again, and
then the hardy seed-eating birds can return from the South much earlier
than their frailer kin."

"Last year," said Rap, "when the men were chopping trees in the great
wood beyond the lake, the miller went up one day to hunt coons and took
me with him. It was the beginning of March and terribly cold; there were
long icicles hanging on the trees, and we were glad enough to go in by
the fire in the lumbermen's camp. But what do you think?--if there
wasn't an Owl's nest, up in a pine tree, with two eggs in it! It was in
a very lonely place, and the miller said the Owl had borrowed an old
Crow's nest and fixed it up a little."

"I should think the eggs would have frozen hard and been spoiled," said
Nat.

"No, t