I have 22 chickens (2 boys and 20 girls) that live with 5 ducks (2 boys and 3 girls). Only once have my ducks been aggressive with a chicken and that was when the rest of the chickens were harassing her. They decided to join in (brats). They’ve all been together for about a year that was the only issue. They have space plenty of roost space and multiple food and water spots available. I didn’t know it wasn’t suggested to keep them together until after they were all together, and not having any issues so far I’m not planning on making a change.