I would see how it goes... If the male has a full train I doubt he would be a yearling...He might be around 3 yrs. It is harder to tell a peahen's age...I would make sure that it is a peahen just incase. A lot of people mistake yearling peacocks for peahens. If your peahen has a brown body, creamy white chest, and a green neck it is a peahen. If she has barring on her back and wings then it is a young peacock. Normally yearlings are not ready to breed, but in some cases as stated above it can happen... Now because the peacock is an adult, and I am guessing if they are ready to breed than the peahen might be too, you need to make sure you pen them for a long time before letting them free-range. Adult peafowl can be harder to keep free-ranging than young peafowl that grew up in your yard, although you still can free-range adults and your chickens might help anchor them there.
I don't know how well they will be for keeping away hawks...My first peafowl were a pair and once I started free-ranging them they were always hidding in the bushes. If they heard or saw a hawk, they would run under the bushes and hide even though they are too big for a hawk, they would still hide. Now all my peafowl are in a pen, but when they see a hawk they look up to the sky and make a certain noise when they see the hawk, but they don't really run and hide. They can spot hawks very well, so maybe the alarm call they make might alert your chickens. They also identify with the call that wild birds make when they see a hawk, and that makes them all stop and look for the hawk. One peafowl breeder has hawk and owl problems and he has lots of peafowl in and out of pens. Although there is one peafowl breeder I have talked to that said one day when a hawk attacked one of her chickens a big group of her peafowl gathered around and scared the hawk away. Also she said that her peacocks scared away a stray dog that came into her yard. She said that her peacocks were flying after the dog and the dog ran away. I guess it depends on the situation...I think peafowl are different for everyone...For some people their peafowl will wander over to the neighbors house or they will wander off into the woods or even run off with some turkeys, for others their peafowl stay in the backyard and will go inside the coop with the chickens at night. I think the only way to know is just to see what happens, so hopefully they will allert your chickens of danger...I don't know about fighting off an attacking hawk though...
