Bird songs are designed to attract a mate or repel a rival, but birds have other things they need to communicate. Pairs need to stay in contact, flocks confer back and forth and a bird that notices a potential attacker will issue a warning. For these and other purposes birds rely on calls—a repertoire of short, unmusical sounds that convey specific information. Unlike a bird’s song, much of which is learned, bird calls are instinctual, an innate means of communicating.