Have they been able to see each other even though separated? that helps them accept the new comers easier. then you can let them out into a common area with treats they love and hopefully they will be more interested in feeding their lil faces than theres a new group of girls in the bunch lets beat them up. lol but like destinduck said there will be a sorting out and your younger girls will be low on the totem pole for a while. 5 months is a good age to let them be together because they will be too young to mate before then. All the best and Welcome.
I'd say in Alaska your into mating season it may just start a little later than the rest of us, and is why your seeing missing neck feather, if your new girls are at least 5 months old you could try them with the adults in a common area first to see how it goes, because believe me the adults ducks can be as hard on the newbies as the drakes as far as pecking. You just don't want to introduce ducks to drakes if they aren't ready for mating, which can be stressful for the ducks, most drakes wouldn't touch them if not ready but if you have one that's hormone crazed you just never know. But try a sneak preview of how they all act if you have a common area [not inside a pen] that way if the youngest start getting pecked on to badly you can put the adults back up. Then wait a couple more weeks before trying intros again. There's always going to be a pecking order so keep that in mind too. I always let mine work out those kinks as long as no one is getting hurt.
