I posted a new gardening question re: potatoes if you can help later with that.
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To answer your question, poultry and avians do seem to go through an adjustment on social pecking order changes. Especially chickens. But ducks do go through this also. And it is possible for them to be a bit too aggressive with each other.
Also unintended consequences can happen also, like with ducks a drake can sometimes try to mate too much with one hen and damage her. But that is less likely to happen with chickens. With chickens you often see them picking on the smallest hen. That can be triggered any time the social order changes or if new chickens enter the flock. But again, chances are a rooster won't be pecked on/picked on.
So it becomes a probability game. What are the chances? The chances are there will be some disruption. It could be small or big disruption. Especially with a lead rooster or lead hen being changed.
Even though your chances are good, you want to lower the stress and chances of something going wrong. And things can go wrong. Therefore to lower those chances and ensure a smooth transition what you can do is put the rooster in a cage (in the shade and) within sight of the other hens that he'll be introduced to. Make sure he won't get heat stroke but you want them to be able to see him, and for him to see them. But not for them to be able to physically interact yet. Do this over the process of a few days, with each day them being closer together and more time with each other.
Then somewhere along the way maybe 3 to 5 days in you can finally set them loose together. You can also let them have chaperoned time together of limited intervals during those days but only with YOU being there to make sure you can interrupt problems before they occur. (Once they start to peck/pick on each other, it sets a pattern that is difficult to disrupt! Be warned!)
This works for both, chickens, ducks, geese. (Hypothesis is that it should work for others including quayle also.)
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Now... what you want to know about this trick is that it ESPECIALLY SHOULD be done this way for new hens and young hens, and younger chicks etc entering your flock. It has less effect with roosters but I'd still do it with them.
I've used this trick with ducks especially many times. Its natural for the animals to try to feel out a pecking order. Therefore young chicks of either species and hens are especially to gain from this.
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Birds that are siblings are less likely to have pecking order problems of any of those species also. But conversely, if they aren't siblings there's a slight chance for increase of this happening.
