"You are right," said the Doctor; "and if you will come here by the window you can watch a pair who are flying in and out of the bird house, on top of the woodshed. Do you hear? Bluebirds have a call-note and a sweet warbling song. As I have told you before, all birds have some note or sound that they use to attract attention or call their mates; but it is only those whose voices are so highly developed that they can make really continuous musical sounds, that are called song birds. "The male is the only real singer in Birdland. Many females have pretty musical notes that they give when about the nest, and some scraps of song; one or two are quite good musicians, but the great chorus comes from the males. "These have their seasons for singing, and are not in equal voice during the entire year. They sing most persistently from the time they put on their spring coat, until after the nesting season, when they take it off. In early autumn some species sing for a time, and in warm climates there is more or less music all winter; but the great morning and evening chorus belongs to spring and the nesting season. It is as rare to hear the perfect song of a bird in autumn, as it is to see its perfect plumage. The young birds of the season are then swelling their little throats in trying to warble a few notes; and as their feathers are a mixture of those worn by their father and mother, such birds and their songs will both, most likely, confuse you. "When you find a strange bird, try to see quickly a few of the things most necessary to naming him. I will make a measure of your middle finger for you such as Olive used to wear. Then you must try to answer the following questions: "How many inches long was he? "What was his general color? "Was his breast plain or speckled? "What was he doing--feeding on the ground or in a tree? "Did he walk with one foot after the other, or hop with both feet together? "Did he sing or only call? "At first you may only remember two or three of these questions, and they will probably be his size, color, and song, if he happens to be singing at the time. "You may not think that a bird, who is hopping about in the grass or flitting among the branches of a tree, is doing anything in particular. But really he may be either collecting material for his nest, or searching for food of some particular kind, in a way which will tell you to what guild of the Bird Brotherhood he belongs. "Everything in the daily life of a bird is interesting. You will find that every bird has its regular times for bathing, pluming, eating, sleeping, working, and playing, all in its own ways, just as you yourselves have. And everything he does is done cheerfully and promptly.