I have observed that my game stags that are penned up separately tend to be slow at feathering out the hackles of the head. Eduardo and Sallie, full siblings of the stags, are about 3 months behind the stags but are not so slow at feathering out around head. This evening I saw why. They engage in allopreening (a.k.a. allogrooming) where they take take turns pulling the sheaths off each others hackle feathers around the head. They expend several minutes at it. The bird being preened seems to solicit by holding area to be serviced in front of other bird. Specific vocalizations may also be associated with behavior. Could not tell who was making them. I have seen bluegill do this but usually for purpose of removing parasites and usually pickers are juveniles while those being picked over are adults. not school / flockmates. Dominiques have not been observed to allopreen which I think is why roosters in particular have rough looking hackle feathers for extended period following feather emergence. Dominique pullets might be doing it based on appearance of feathers.