The song of the male nightingale tells females how good a father he will be, according to research. The study shows that better singers will feed their offspring more often, and that they advertise this to potential mates by singing in a more orderly way through repeating song sequences, and using more variable song, including many different 'buzz,' 'whistle' and 'trill' songs.

Source: Nightingales show off their fathering skills through song