word of warning ducks and chickens can be raised together and even housed together, they won't separate other than to sleep, but if you have a rooster in the flock you need to keep him locked up separetely especially if he's not got older hens that school him.
we had the whole flock in an uproar this week, due to the Rooster decided he wanted to breed anything that moved as nobody was receptive he tried the duck hen and drake, thankfully we found a breeder with some slightly older hens and they schooled him so now he isn't terrorizing everyone.
My mallard drake isn't acting like this but he's got the blue Swedish hen, she normally schools them all if they get out of hand