I’ve seen my chook preening other chickens

[SomeChookLover]

This isn’t particularly urgent, more of a mild curiosity I’ve had after seeing my oldest hen, Duck (don’t worry about the name) preening two other hens.
I know chickens like to preen in groups, but I’ve never seen a chicken preening another chook. Duck is currently at the top of the hen pecking order, and I’ve seen her preening Charlottes head feathers (Charlotte is second in the pecking order) and Morgan more recently (third in the pecking order.)
Duck did raise Charlotte, so I thought it could be something to do with that, but she didn’t raise Morgan so it doesn’t make much sense.
My current theory (assuming Duck isn’t just being nice) is that she might be being nice to the hens who will be top of the pecking order next? Kind of mentoring them or something. I don’t really know.
One more thing is that Duck was really good friends with the head hen before her, so maybe she just thinks it’s normal.
I haven’t been able to find really any information on it, but I’m really just wondering whether this is normal or if there’s an explanation?

 

[chooki]

My chickens preen each others every now and then, especially after heavy rainfall when free ranging outside. One of them even preens me when she is allowed to be high enough. I end up with chicken saliva gel on my hair for the rest of the day until I take a shower and wash my hair. Sometimes, one of them will preen another's face feather, while the other one stands very still.
My chooks have either been raised up together or grew up in the flock.

 

[Moodleroni]

My hens preen my head roo all the time. I thought it was normal, never thought anything of it.
They also softly pick off leftover food from each others faces/beaks, especially after eating tomatoes or when I turn their crumble into mash

 

[Perris]

@SomeChookLover It is normal, and a sign of a happy healthy flock. It's called allopreening; try searching on that term and you should find more information.

 

[rosemarythyme]

It's a social activity. Hens are more likely to groom other hens they're close to (or roosters they favor) or to clean off feed from messy eaters.