I’ve always wondered about the egg song. I’d think announcing to all the predators in the area that you just laid an egg wouldn’t be the best idea.
What I read or heard somewhere is that the egg song is not to announce that the hen laid an egg, but rather it is to announce "Hey where is everybody?" The thought is that "in the wild" a flock of chickens would continue to move around and the hen needed to know where to find her flock when she was done. Usually ( at least at my house) the egg song is answered by the flock & rooster, so the hen knows where to find the flock!
12 eggs at my house today. The Barred rock was back on the nest again this evening, but was not there all day and there were NO eggs in that nest this morning, so maybe she has just decided to sleep in the nest box?