"...[when they] sing alone, they leave longer gaps than they would do when singing together. This suggests that they tailor the timing of their notes to what their partners are doing, using each syllable as a cue to produce the next one. That became obvious when the males screw up (and they often do). In several of Fortune’s recordings, the males often fumbled their notes in the middle of long sequences. When this happened, the females carried on and left longer gaps than usual between their syllables. It seems the female takes the lead in the duet, setting the rhythm that the male then follows."
What is being talked about isn't musicians, or human singers, but wrens. Songbirds working as a musical partnership.