First off. Good job on deciding to make a Chicken Coop. It's a really big help.
I..what? If you take your chicken out of a coop and place them on a ground they will de-spawn. It is impossible to keep non-domesticated animals in a fence or palisade without them de-spawning. I've tried

(If you leave out chickens they will go away.)
You have to keep a regular supply of food in their coop. You left click the straw,seed,etc. from your inventory and right click the coop. Their quality depends on the quality of food you give them.
You don't leave seeds around, because the chickens never go out of the coop unless you make them. (I take my chickens out for walks because I can. E-Chickens have to be e-fit.)
If you have any more questions feel free to ask or look at the wiki. Cheers, mate.