if you have mice, you probably do not have rats near by (rats will compete with mice and kick mice out).
Your chickens are most likely not afraid of teh mice because way before you noticed you had mice they'd have been there and the chickens got used to them. They're staeling your chickens feed which is simple enough....
also don't say the mice cant get into your nesting area...if your chickens can, the mice most deffiantly can.
Poison should not be an option here because we have tried that before and mice actually stoored poisoin in myrabbits cages AND in the house in my shoes. My brother actually woke up one morning with a poison pellet on his chest!!! Evil sneaky lil field mice!!! LOL!
If it was me, outside of the coop i'd put snap traps, and live traps inside the coops. LIve traps are awesome..and miec go right in thinking they can get out and ha...they can't
Then if your'e the heart type, drive a few miles down the road and letit go....or shake the live trap like crazy for about a min and the mouse will either be dead or close to it then let it out and kill it.
Just my thoughts advice etc