Mr. Bobolink ends his wildest songs when the little birds come from the shells. Their mouths are always wide open, crying for food. Mr. Bobolink is very busy feeding his children. He flies back and forth all day long, bringing insects to his nursery. The gay concerts are ended. At this time, too, Mr. Bobolink changes his clothes. He puts on a working suit, with more brown in it. His gay plumes do not come back until the next spring. After the little ones learn to fly, in August, if it is hot, the whole family may go to Canada, for a trip. But as soon as the cool September mornings come, all the bobolinks think of the South. They gather in great companies, and turn their heads toward the West Indies. Now and then, they may rest for a few hours, or a warm day or so, but they fly pretty steadily southward. When cold weather has come, we see no more bobolinks. They are all busy eating and singing in the sunny tropic lands. I wish you would all read, and perhaps learn to recite a charming poem called “Robert o’ Lincoln.” It was written, by the great poet Bryant, about this little bird of many names, and many homes. Now from the story of the bobolink, you see the manner of this migration of birds. You see _why_ birds migrate. It is to keep where they find the food and the weather which they prefer. Its _cause_ is the change of the season. As the season changes the food changes. Some birds move away because it is growing too hot where they are, and they like cooler places. Again, there are birds which stay near us in the winter, and fly North in the summer, almost to the land of constant snow. Those birds which breed in the cold polar regions often find a winter home in the Northern States. But some birds which breed in the coldest climates fly to hot countries for their winter of rest and play. When birds come in the spring, and leave in the fall, they rear their young where they make their summer home. We call them our summer birds. Our winter birds are those which come to us in the cold weather, do not build nests near us, but fly away when the season grows warm. While they stay near us, they take shelter at night in shrubs or evergreen trees. What we call birds of passage are birds that stop with us for only a few days, as they are flying long distances, half round the world, perhaps. Then there are birds, as the robin, sparrow, thrush, which may stay all the year round near one place. In the warm weather they build nests, and rear their young. In cold weather, such birds are often driven near houses and barns to get food. Crows may stay all winter in one place if food is plenty. If they cannot find enough to eat, they gather in great numbers, and fly to places where they will get more food.