Rockin' Robins

 Ever wonder why a robin is sometimes referred to as a "Rockin' Robin", like the song by Bobby Day?

Picture from Wikipedia

 It's because the male American Robin has an almost rocking!  He has a continuous song, most commonly described as a cheerily carol.  It's made up of discrete units and repeated with brief pauses in between.  In addition to its song, the American Robin has numerous calls used for communicating specific information, such as when a ground predator approaches or when a nest or Robin is being directly threatened.