I agree with Miss Prissy & ChickNLittle and will relate a little vignette from my childhood that I think illustrates why they don't mix well.
I had my first chickens as a kid. They were my pets and their care was my job. We only ever had 2 or 3 hens at a time (we lived in the suburbs). So one year when I was 10 or 11 my older brother's friend came over with several Easter chicks (I didn't know what the heck they were at the time but I now know they were a Black Austrolorp and 2 EEs) and 3 ducklings. Not knowing any better, we put them all together and I got a small swimming pool (5 ft across??) for the ducks. You'd clean and fill that swimming pool and 1 hour later it was the blackest, nastiest water you ever saw or smelled! The whole chicken run was always wet and nasty while we had the ducks, but of course not so when we only had chickens. So in time the ducks grew to adult size and bullied the hens mercilessly. Not only did they chase them around and keep them away from food just for kicks, the male ducks (we had 2 males, 1 female) appeared to be sexually assaulting the hens. Yes! I kid you not! Finally, in under 1 year, we decided we were done with ducks. We couldn't find a home for them, so my parents decided to take them to a local park and "let them go" with a big mixed flock of ?feral/wild? white ducks and mallards on a big pond. Don't know if they were able to survive there after being raised by us, and it is not what I'd do now as an animal owner if I needed to re-home an animal. But our hens were SOOOOOO glad they were gone. I see ducklings at the feed store now and am not even tempted, I will never forget regularly cleaning that filthy Smurfs swimming pool! Now if I had a pond.......
Now consider the source of this story, the reflections of a 10 year old whose parents didn't really ensure our animal husbandry skills were up to snuff, but I do think it shows that ducks and chickens don't mix. Good luck!