A、They hide themselves. B、They keep silent. C、They stay away from other birds. D、They make some signs. DWhat do most birds usual

People usually sing because they like music or because they feel happy. They express their happiness by singing. When a bird sings, however, its song usually means much more than that a bird is in a good temper. Birds have many reasons for singing. They sing to give information.
    Their songs are their language. Love songs are sung by male birds. They sing when they want to attract a female bird. It is their way of saying that they are looking for a wife. Birds also sing to tell other birds to keep away. To a bird, his tree, or even a branch of tree is his home. He does not want strangers to come near his home. So he sings to warn them. If a bird can not sing well, he usually has some other means of giving important information. Stone birds dance, spread out their tails, or make other signs. There is also a special kind of bird which builds a small garden of stones and flowers to attract a female bird.