The few times I've seen hens sit on other hens it was about dominance.I'm not sure if its the same thing but I have seen several hens in my flock do what looks like a mount/not a mount. Morrigu does it fairly regularly to the junior Campines. I've seen Mhari do it to the Wyandottes. It doesn't seem to be about sex with my lot but about dominance & who's who in the rankings. Aoife will be rather pushy & Morrigu will run her down & do the mount thing. She seems to prefer to grab onto the neck feathers but Aoife's quite a bit bigger than she is. Mhari did it to Wrold last night over a feeding dispute. All Wrold did was flare her hackles when Mhari was done.