Birdsong is a type of vocalization used by birds to communicate with each other. It can range from simple chirps and calls to complex melodies. The term 'WARBLE' refers to a type of birdsong that is melodic and often includes trills and variations in pitch. A 'CALL' is a short, sharp sound made by a bird to signal its presence or to alert other birds to danger. 'CHIRRUP' is a soft, repetitive sound made by some birds, usually as a form of communication. 'Otis' is a type of birdsong that is characterized by a series of short, high-pitched notes. Finally, 'twitters' are a series of short, high-pitched notes that are often used by small birds to communicate with each other.