Virginia Rails, Clapper Rails, Soras, Moorhens, Bitterns and sometimes Coots like to perform this act, which I call a synchophony. This happens fairly frequently when something disturbs the peace of the marsh and several birds call in response at once. In this sample a Great Blue Heron circles over and calls, and first a Bittern or Rail, then two Soras, another Virginia and finally another Sora join in the "synchophony". I have recorded instances when a barking dog, an airplane, and other rails have set off the phenomenon. I'm not sure what purpose this [chorus] serves, but it occupies a significant amount of my thinking time. It's most probably a general alarm in the marsh - A Great Blue, a dog and an overhead airplane might all be considered risks if you're a rail - and note that the participants are generally Rail-family birds or birds with rail-y behavior, who are used to communicating primarily vocally (they can't see each other in the marsh).

Douglas Von Gausig (recordist, copyright holder), Naturesongs.com