The theory goes that the "egg song" is basically "I'm done, come get me". In the wild, flocks range around a large area, and they're not going to be held back from finding food by the hens who need to use the favored bush. So, after she sits there for a while, however long it takes, the flock is usually in a totally different position than when she left. It's not safe for her to be wandering around alone looking for them, so she calls her husband. He responds in one of two ways...
Either with a call back, "We're over here, we're busy, c'mon over!" "No really hun, I didn't see any monsters, c'mon!"
Or he will herd the whole flock back over to the favorite bush area and personally fetch the hen getting off the pot. Hens really prefer roosters who treat them courteously this way. Their egg songs are noticeably shorter and less whiny.
Roosters tend to stick with a method depending on their personality. At least that I have witnessed. But it can be affected by a few things. Like how big the ranging flock of hens is and how willing they are to leave their foraging, if they're finding goodies or not. He usually won't abandon them for the one that's in the bush he deemed "safe" for laying.
I have also seen a roo who so totally wasn't enamored of two hens, that he wouldn't come back for them, while he would always escort the others. Those were the most annoying, shriekiest hens I have ever witnessed, they would go on and on for hours. The roo would call back a few times, but he seemed to consider them high maintenance.
