Chickenology: Promoting Biological Rodent Control
If you have poultry you are going to be seeing this:
And if you provide whole grain rations to your birds, it's a given that you'll see this as well.
Poultry are messy animals...they scatter food everywhere. I have tried and failed to control this mess. The whole grain rations get shared with the local wild bird populations, and I'm good with that. 
However, I draw the line at rats and mice. I actually have never had a rat problem, and I have not ever heard of anyone in my area with rat problems, but I have had mouse problems. I have tried drowning them out. I have tried poisoning them out. I've even spent a few memorable evenings with a pellet rifle mounted with a home made night scope, sniping away at the little furry bandits; which by the way, was soooo much fun.
My final solution is absolutely not for everyone, but wow is it effective.
I have not only a fondness for living creatures, but I have a fondness for solutions. This has been a huge solution for me. 
A couple years ago, I was out hunting during the fall dove hunt, and I came across a Garter Snake with 3 large lumps in its body. I picked it up and it spit out 3 mice. Light bulb went off. Garter Snakes are fairly small as snakes go...they are voracious predators and they are too small to bother chickens. I knew where to get a few. 
I started with a big pregnant female that I caught, less than a block from my home. Her name is "BITER". She has now been around our home for 4 years and has had several batches of babies. Over the years I have seen Biter and her companions (she does attract males each spring) sunning in the Tiger Lillies in the front of the house. They also like the railroad ties along the east side of the front yard. When they get hungry and the night crawlers haven't been coming up at night, I'll see them working their way along the side of the house towards the coop, or if I EVER see a mouse scurry across the back patio in the evening, I'll go catch Biter and let her go under the coop...she doesn't try to bite anymore, or spray musk...but the name has stuck.
I have a trampoline in my backyard, you can see it in the above photo. It is sunk into the ground and is lined with concrete blocks. The snakes hibernate inside the hollows of the concrete blocks. They come out each spring, and within a few weeks I'll start to see the next batch of Biter's babies hunting night crawlers in the garden or sunning themselves in the Tiger Lillies in the front yard. 
The chickens will make a very specific sound when they see a snake in the yard, I've heard this sound only when a snake is present...and all the girls are alert. So...when I'm in the house and hear this sound coming from my girls out in the yard, I know that Biter and her crew are at work.
The snake in the picture that I posted above is one of Biter's daughters. She was sunning herself on a railroad tie in the front yard and I picked her up for the photo. She was a bit put out by the experience, but was soon back to sunning herself again. 
Biter and her progeny are great mousers, better than any cat I have ever owned. I have not had a mouse problem in 3 years. 
It's an "Outside the Box" solution and it works great. But yeah...not for everybody.