There is still another point to know. One bird does not always sing the same song. I have heard a song sparrow sing five or six different songs, standing all the time in plain sight on a fence. In the same way I have known a meadowlark to make six changes in his few notes. Besides their own natural songs, many birds like to copy the notes of others. Our mockingbird is very fond of learning new things, and he does not always choose songs either. He will imitate the noise of filing a saw, or the pop of a cork, as readily as the sweetest song. I have heard one sing the canary's song better than the canary himself. [Illustration: INDIGO-BIRD] Other birds can do the same. A common English sparrow picked up in the streets of a big city, hurt, and not able to fly, was put into a room with a canary. No doubt the wild bird found his life in a cage rather dull, after having been used to the streets, and he soon began to amuse himself trying to do as the canary did, to sing. In a few weeks he learned the whole song, and he could sing it even better than his roommate, for his voice was full and rich, and not so shrill as the canary's. Most people think that birds sing all summer. They think so because they have not taken notice. We who are very fond of bird song know it is not so. Singing begins when the birds first come in the spring. It goes on while the nest is being built, and the mother bird is sitting. The father has little to do at that time, and so he sings. And besides, he seems to be so happy that he cannot help it. But when little ones begin to call for food, he has to be very busy, and does not have so much time for music. Some birds stop singing as soon as they go to feeding. But not all do so. Many go on singing till they begin to change their clothes, or to moult, as it is called. This happens in August or September, and when it begins, a bird seems to lose his voice. One of the first to stop singing is the bobolink. He is rarely heard after June is past. The veery is another whose singing days are over early. You may hear his call in the woods, if you know it, but not a song will you hear after the middle of July. By the time August comes in, almost every bird is silent, except for his calls or "talk." The birds to be heard then are the red-eyed vireo, who seems never to tire, and now and then the indigo-bird, or the wood pewee, and best of all, the dear little song sparrow, who keeps up his cheery songs till the very last. Then you will know that all the birds are busy putting on their new suits for their long journey. XII WHAT HE EATS WHAT the bird eats and where he gets his food are useful things for us to know. It has only lately been found out that birds are the most valuable of helpers to us. What we cannot eat ourselves, they are happy to live on, and things that make us a great deal of trouble are their daily food.