“They have nests there now,” said Rap eagerly; “a great many nests, and they are very pretty.  Ah!  There is the big brown bird that you call a Thrasher, with his striped breast and long tail that spreads like a fan.  I see him—­he is building in that barberry bush!”

“Then the nest comes pretty soon after the up-journey,” said Nat.

“Yes,” answered the Doctor, as he watched the antics of the Thrasher; “right after the journey the mate, and next the nest.  Do not forget the mate, Nat, for it is Mrs. Bird who usually makes the nest and always lays the eggs, besides working in the guilds with her husband, whose greatest distinction is in being the family musician.”

“When do the Summer Citizens begin to come back to their nesting places?” asked Nat.  “And when do they go away again?”

“The great bird procession begins the first of March with Bluebirds, Robins, Redwings, and Meadowlarks, but it is the first of June before the latest comers, the little Marsh Wrens, are settled.  Then in autumn, from September until the first snows of 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.”