Meaning: This sentence describes the way birds sing. It's like saying,
Choice of Words: "Beaks" are the mouths of birds. "Open" means to move apart or become wider. "Wide" means having a large distance from one side to the other. "Sing" means to produce musical sounds with the voice. "Beautiful" means very pleasing to the eye or ear. "Songs" are pieces of music. When you put it together, it means birds open their mouths wide to produce beautiful music.