I have an ongoing rat problem around my chicken coop. Both "tree" and Norwegian varieties.
I was putting down pelletized rat poison in the shed I keep the feed in and it was disappearing in prodigious quantities, but no evidence of dead rats anywhere.
Then one day after a rain storm, I noticed little raccoon footy-prints in the mud around the shed. A-HA! sez I, and break out the Havahart trap. Went down the next morning and "Oh, goody! The trap is sprung"
Got a closer look and now it's "Oh S**t! It's a skunk!"
Threw a blanket over the trap, hauled it outside, propped the door open and un-@$$ed the area. Went back down a couple of hours later and the trap is empty...whew!
Did eventually trap one coon and he seemed a little anemic so I gave him a lead injection. Apparently, that wasn't the problem, he croaked anyway...
Metal cans with lids bungied down seems to work for protecting the feed, but still have the occasional rat in the coop cleaning up what the birds scatter around while eating. Tomcat bait strategically placed cures it for a while, but have to do that about every 3 months for a few days.