Most times they are fine together... but all the birds have different personalities just like people.. and some just won't get along.I already view Merry and Pippin and family members. No different from my bunny or dog, so I don't think I could ever part with them or any others. If I'm not careful I'll end up with way too many ducks! Out of curiosity, why can't chickens and ducks be housed together? Will they peck each other? I have a friend who keeps them together without issues, but I have not tried it myself obviously.
If they have a lot of space then they should be fine... so they can get away from each other.
Sometimes a male duck will try to mate with a chicken and injure it...
I keep mine together when they are smaller.. then house the ducks on their own.... there was never any fighting... but the ducks are very messy and smelly and messed up the chicken coop bad. When they are not in there its lovely and dry and clean and does not smell... when they are in there they wet everything and throw food everywhere and poop so much that the floor ends up damp, slimy and very smelly.. then the hens get dirty and carry the dirt up to the roost and nest boxes off their feet.