I must remind readers that my birds at not separated by sex, but are free to function as a community of family and friends during breeding as well as non-breeding time, in an environment which allows for full flight. This is probably why I am witnessing behaviors which might not be as apparent in other types of aviaries. Also, I am not a production breeder. I allow birds to breed because it is natural and because it is their desire to do so. In Part I, I elaborated on the cock's song which is the flashiest and most easily understandable form of communication in cockatiels.
Cockatiels communicate vocally with each other quite a bit.
I have found this to be particularly true since I have allowed my birds complete freedom, as cages greatly restrict their natural tendencies. It sounds like one bird making both sounds. At times, one pair will communicate with another in the same fashion, with one member of a pair issuing the higher note, while a member of the other pair takes the lower note. Members of a bonded pair will use the same communication when one member is in the nestbox, and the other is out for recreation or guard duty, just to check on each other's welfare. There's another sound made when the incubation shift is about to change, and one member is getting ready to relieve the other for sitting on eggs.