+1
Tree rats - 22LR
If I were to have to get a new one. I would look at a Cz 452 American or American 16" and use a standard velocity 38 or 40 grain bullet. the hyper velocity stuff makes a mess. the standard or target stuff makes a 22 hole in and out.
The other neat thing is the longer barreled guns, especally the tube fed guns can shoot the CCI CB Longs. the little bullet makes very little noise and in the early fall as the season opens more tree rats seem to come out to see what was that strange snap noise. They are good out of my CZ 452 Lux up to 75 feet and have taken many a cotton tail too.
For ground squirrels the 17HMR is the choice.
the little bullet turns into schrapnell and does not fly far but the 22LR, even the hyper stuff, will hit a rock and you hear the zing of a lead hunk zipping off at an odd angle.
The 22 mag is also a great round if you have other things to shoot in the woods. Raccoon, bob cat, fox, coyote, or ground hog for tree rats.
the Hyper 30 to 34 grain stuff gives you great "style points" as ground squirrels, ghophers, or other vermin varmints are hit.
Style points are how many flips, parts fly off, or a full decapitation.