I have noticed some of my girls do the egg song and some don't.
I have also heard the song coming from out doors where they should not be laying, while they are free ranging.
Because I'm afraid that they'll start laying out doors, I jump up and try to inspect the area for wayward eggs.
I've noticed that quite often when I hear the egg song it seems that the hen has somehow lost sight of the flock and appears to be
calling out, "HEY, where is everybody?".
I don't hear much from them early in the morning while they are locked up and when the bulk of the eggs are being laid.
It's more from the later layers and solitary birds.
So I wonder if it more of a social call than an egg proclamation?